Use of ADP/ATP transporter genes to increase nitrogen use efficiency and low nitrogen tolerance to a plant

This application is a division of U.S. patent application Ser. No. 13/059,231 filed Feb. 16, 2011, which is a National Phase of PCT Patent Application No. PCT/IB2009/053633 having International filing date of Aug. 18, 2009, which claims the benefit of priority of U.S. Provisional Patent Application No. 61/136,189 filed on Aug. 18, 2008. The contents of the above applications are all incorporated by reference as if fully set forth herein in their entirety.

The ASCII file, entitled 61683SequenceListing.txt, created on Feb. 16, 2015, comprising 5,350,431 bytes, submitted concurrently with the filing of this application is incorporated herein by reference.

The present invention, in some embodiments thereof, relates to isolated polypeptides and polynucleotides, nucleic acid constructs comprising same, transgenic plants expressing same and methods of using same for increasing nitrogen use efficiency, yield, biomass, vigor, growth rate, oil content, fertilizer use efficiency, water use efficiency and abiotic stress tolerance of a plant.

A common approach to promote plant growth has been, and continues to be, the use of natural as well as synthetic nutrients (fertilizers). Thus, fertilizers are the fuel behind the “green revolution”, directly responsible for the exceptional increase in crop yields during the last 40 years, and are considered the number one overhead expense in agriculture. Of the three macronutrients provided as main fertilizers [Nitrogen (N), Phosphate (P) and Potassium (K)], nitrogen is the only one that usually needs to be replenished every year, particularly for cereals, which comprise more than half of the cultivated areas worldwide. For example, inorganic nitrogenous fertilizers such as ammonium nitrate, potassium nitrate, or urea, typically accounts for 40% of the costs associated with crops such as corn and wheat.

Nitrogen is an essential macronutrient for the plant, responsible for biosynthesis of amino and nucleic acids, prosthetic groups, plant hormones, plant chemical defenses, etc. In addition, nitrogen is often the rate-limiting element in plant growth and all field crops have a fundamental dependence on inorganic nitrogen. Thus, nitrogen is to translocated to the shoot, where it is stored in the leaves and stalk during the rapid step of plant development and up until flowering. In corn for example, plants accumulate the bulk of their organic nitrogen during the period of grain germination, and until flowering. Once fertilization of the plant has occurred, grains begin to form and become the main sink of plant nitrogen. The stored nitrogen can be then redistributed from the leaves and stalk that served as storage compartments until grain formation.

Since fertilizer is rapidly depleted from most soil types, it must be supplied to growing crops two or three times during the growing season. In addition, the low nitrogen use efficiency (NUE) of the main crops (e.g., in the range of only 30-70%) negatively affects the input expenses for the farmer, due to the excess fertilizer applied. Moreover, the over and inefficient use of fertilizers are major factors responsible for environmental problems such as eutrophication of groundwater, lakes, rivers and seas, nitrate pollution in drinking water which can cause methemoglobinemia, phosphate pollution, atmospheric pollution and the like. However, in spite of the negative impact of fertilizers on the environment, and the limits on fertilizer use, which have been legislated in several countries, the use of fertilizers is expected to increase in order support food and fiber production for rapid population growth on limited land resources. For example, it has been estimated that by 2050, more than 150 million tons of nitrogenous fertilizer will be used worldwide annually.

Increased use efficiency of nitrogen by plants should enable crops to be cultivated with lower fertilizer input, or alternatively to be cultivated on soils of poorer quality and would therefore have significant economic impact in both developed and developing agricultural systems.

Genetic improvement of fertilizer use efficiency (FUE) in plants can be generated either via traditional breeding or via genetic engineering.

Attempts to generate plants with increased FUE have been described in U.S. Pat. Appl. No. 20020046419 to Choo, et al.; U.S. Pat. Appl. No. 2005010879 to Edgerton et al.; U.S. Pat. Appl. No. 20060179511 to Chomet et al.; Good, A, et al. 2007 (Engineering nitrogen use efficiency with alanine aminotransferase. Canadian Journal of Botany 85: 252-262); and Good A G et al. 2004 (Trends Plant Sci. 9:597-605).

Yanagisawa et al. (Proc. Natl. Acad. Sci. U.S.A. 2004 101:7833-8) describe Dof1 transgenic plants which exhibit improved growth under low-nitrogen conditions.

U.S. Pat. No. 6,084,153 to Good et al. discloses the use of a stress responsive promoter to control the expression of Alanine Amine Transferase (AlaAT) and transgenic canola plants with improved drought and nitrogen deficiency tolerance when compared to control plants.

The global shortage of water supply, desertification, abiotic stress (ABS) conditions (e.g., drought, salinity, osmoticum, flood, suboptimal temperatures such as cold and heat, toxic chemical pollution, radiation, nutrient deficiencies, and the like) together with the presence of limited nitrogen and fertilizer sources cause substantial damage to agricultural plants such as major alterations in the plant metabolism, cell death, and decreases in plant growth and crop productivity.

Drought is a gradual phenomenon, which involves periods of abnormally dry weather that persists long enough to produce serious hydrologic imbalances such as crop damage, water supply shortage and increased susceptibility to various diseases.

Salinity affects one in five hectares of irrigated land. None of the top five food crops, i.e., wheat, corn, rice, potatoes, and soybean, can tolerate excessive salt. Detrimental effects of salt on plants result from both water deficit, which leads to osmotic stress (similar to drought stress), and the effect of excess sodium ions on critical biochemical processes. As with freezing and drought, high salt causes water deficit; and the presence of high salt makes it difficult for plant roots to extract water from their environment. Thus, salination of soils that are used for agricultural production is a significant and increasing problem in regions that rely heavily on agriculture, and is worsen by over-utilization, over-fertilization and water shortage, typically caused by climatic change and the demands of increasing population.

Extreme temperatures such as suboptimal or heat temperatures affect plant growth and development through the whole plant life cycle. Thus, low temperatures reduce germination rate and high temperatures result in leaf necrosis. In addition, mature plants that are exposed to excess of heat may experience heat shock, which may arise in various organs, including leaves and particularly fruit, when transpiration is insufficient to overcome heat stress. Heat also damages cellular structures, including organelles and cytoskeleton, and impairs membrane function. Heat shock may produce a decrease in overall protein synthesis, accompanied by expression of heat shock proteins, e.g., chaperones, which are involved in refolding proteins denatured by heat. High-temperature damage to pollen almost always occurs in conjunction with drought stress, and rarely occurs under well-watered conditions. Combined stress can alter plant metabolism in novel ways. Excessive chilling conditions, e.g., low, but above freezing, temperatures affect crops of tropical origins, such as soybean, rice, maize, and cotton. Typical chilling damage includes wilting, necrosis, chlorosis or leakage of ions from cell membranes. Excessive light conditions, which occur under clear atmospheric conditions subsequent to cold late summer/autumn nights, can lead to photoinhibition of photosynthesis (disruption of photosynthesis). In addition, chilling may lead to yield losses and lower product quality through the delayed ripening of maize.

Nutrient deficiencies cause adaptations of the root architecture, particularly notably for example is the root proliferation within nutrient rich patches to increase nutrient uptake. Nutrient deficiencies cause also the activation of plant metabolic pathways which maximize the absorption, assimilation and distribution processes such as by activating architectural changes. Engineering the expression of the triggered genes may cause the plant to exhibit the architectural changes and enhanced metabolism also under other conditions.

In addition, it is widely known that the plants usually respond to water deficiency by creating a deeper root system that allows access to moisture located in deeper soil layers. Triggering this effect will allow the plants to access nutrients and water located in deeper soil horizons particularly those readily dissolved in water like nitrates.

Yield is affected by various factors, such as, the number and size of the plant organs, plant architecture (for example, the number of branches), grains set length, number of filled grains, vigor (e.g. seedling), growth rate, root development, utilization of water, nutrients (e.g., nitrogen) and fertilizers, and stress tolerance.

Crops such as, corn, rice, wheat, canola and soybean account for over half of total human caloric intake, whether through direct consumption of the seeds themselves or through consumption of meat products raised on processed seeds or forage. Seeds are also a source of sugars, proteins and oils and metabolites used in industrial processes. The ability to increase plant yield, whether through increase dry matter accumulation rate, modifying cellulose or lignin composition, increase stalk strength, enlarge meristem size, change of plant branching pattern, erectness of leaves, increase in fertilization efficiency, enhanced seed dry matter accumulation rate, modification of seed development, enhanced seed filling or by increasing the content of oil, starch or protein in the seeds would have many applications in agricultural and non-agricultural uses such as in the biotechnological production of pharmaceuticals, antibodies or vaccines.

WO publication No. 2009/013750 discloses genes, constructs and methods of increasing abiotic stress tolerance, biomass and/or yield in plants generated thereby.

WO publication No. 2008/122980 discloses genes constructs and methods for increasing oil content, growth rate and biomass of plants.

WO publication No. 2008/075364 discloses polynucleotides involved in plant fiber development and methods of using same.

WO publication No. 2007/049275 discloses isolated polypeptides, polynucleotides encoding same, transgenic plants expressing same and methods of using same for increasing fertilizer use efficiency, plant abiotic stress tolerance and biomass.

WO publication No. 2004/104162 discloses methods of increasing abiotic stress tolerance and/or biomass in plants and plants generated thereby.

WO publication No. 2005/121364 discloses polynucleotides and polypeptides involved in plant fiber development and methods of using same for improving fiber quality, yield and/or biomass of a fiber producing plant.

WO publication No. 2007/020638 discloses methods of increasing abiotic stress tolerance and/or biomass in plants and plants generated thereby.

According to an aspect of some embodiments of the present invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of a plant, comprising expressing within the plant an exogenous polynucleotide comprising a nucleic acid sequence at least 80% identical to SEQ ID NO: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2521 or 2522, thereby increasing the nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of the plant.

According to an aspect of some embodiments of the present invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of a plant, comprising expressing within the plant an exogenous polynucleotide comprising the nucleic acid sequence selected from the group consisting of SEQ ID NOs: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522, 3, 5, 6, 9, 10, 14, 15, 20, 61, 62, 129, 288, 294, 307, 363, 667, 668, 669, 670, 672, 2398-2413, 2456 and 2457, thereby increasing the nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of the plant.

According to an aspect of some embodiments of the present invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of a plant, comprising expressing within the plant an exogenous polynucleotide comprising a nucleic acid sequence encoding a polypeptide at least 80% identical to SEQ ID NO: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2562 or 2563, thereby increasing the nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of the plant.

According to an aspect of some embodiments of the present invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of a plant, comprising expressing within the plant an exogenous polynucleotide comprising a nucleic acid sequence encoding a polypeptide selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563, 138-143, 146, 148, 150-152, 157, 162, 198, 265, 1334-1350, 1352-1364, 1426-1428, 1458, 1460, 1732-1734, 1737-1738, 2523-2532, 2542 and 2543, thereby increasing the nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of the plant.

According to an aspect of some embodiments of the present invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency and/or oil content of a plant, comprising expressing within the plant an exogenous polynucleotide comprising a nucleic acid sequence at least 80% identical to SEQ ID NO: 3, 5, 6, 9, 10, 14, 15, 288, 294, 2398-2412 or 2413, thereby increasing the nitrogen use efficiency, fertilizer use efficiency, and/or oil content of the plant.

According to an aspect of some embodiments of the present invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency and/or oil content of a plant, comprising expressing within the plant an exogenous polynucleotide comprising the nucleic acid sequence selected from the group consisting of SEQ ID NOs: 3, 5, 6, 9, 10, 14, 15, 288, 294, 2398-2413, thereby increasing the nitrogen use efficiency, fertilizer use efficiency and/or oil content of the plant.

According to an aspect of some embodiments of the present invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency and/or oil content of a plant, comprising expressing within the plant an exogenous polynucleotide comprising a nucleic acid sequence encoding a polypeptide at least 80% identical to SEQ ID NO: 138-153, 1334-1350, 1352-1364, 1458, 1460, 2523-2531 or 2532, thereby increasing the nitrogen use efficiency, fertilizer use efficiency and/or oil content of the plant.

According to an aspect of some embodiments of the present invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency and/or oil content of a plant, comprising expressing within the plant an exogenous polynucleotide comprising a nucleic acid sequence encoding a polypeptide selected from the group consisting of SEQ ID NOs: 138-153, 1334-1350, 1352-1364, 1458, 1460, 2523-2532, thereby increasing the nitrogen use efficiency, fertilizer use efficiency and/or oil content of the plant.

According to an aspect of some embodiments of the present invention there is provided an isolated polynucleotide comprising a nucleic acid sequence at least 80% identical to SEQ ID NO: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2521 or 2522, wherein the nucleic acid sequence is capable of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress of a plant.

According to an aspect of some embodiments of the present invention there is provided an isolated polynucleotide comprising the nucleic acid sequence selected from the group consisting of SEQ ID NOs: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522, 3, 5, 6, 9, 10, 14, 15, 20, 61, 62, 129, 288, 294, 307, 363, 667, 668, 669, 670, 672, 2398-2413, 2456 and 2457.

According to an aspect of some embodiments of the present invention there is provided an isolated polynucleotide comprising a nucleic acid sequence encoding a polypeptide which comprises an amino acid sequence at least 80% homologous to the amino acid sequence set forth in SEQ ID NO: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2562 or 2563, wherein the amino acid sequence is capable of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of a plant.

According to an aspect of some embodiments of the present invention there is provided an isolated polynucleotide comprising a nucleic acid sequence encoding a polypeptide which comprises the amino acid sequence selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563, 138-143, 146, 148, 150-152, 157, 162, 198, 265, 1334-1350, 1352-1364, 1426-1428, 1458, 1460, 1732-1734, 1737-1738, 2523-2532, 2542 and 2543.

According to an aspect of some embodiments of the present invention there is provided a nucleic acid construct comprising the isolated polynucleotide of the invention, and a promoter for directing transcription of the nucleic acid sequence in a host cell.

According to an aspect of some embodiments of the present invention there is provided an isolated polypeptide comprising an amino acid sequence at least 80% homologous to SEQ ID NO: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2562 or 2563, wherein the amino acid sequence is capable of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of a plant.

According to an aspect of some embodiments of the present invention there is provided an isolated polypeptide comprising the amino acid sequence selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563, 138-143, 146, 148, 150-152, 157, 162, 198, 265, 1334-1350, 1352-1364, 1426-1428, 1458, 1460, 1732-1734, 1737-1738, 2523-2532, 2542 and 2543.

According to an aspect of some embodiments of the present invention there is provided a plant cell exogenously expressing the polynucleotide of the invention, or the nucleic acid construct of the invention.

According to an aspect of some embodiments of the present invention there is provided a plant cell exogenously expressing the polypeptide of the invention.

According to some embodiments of the invention, the nucleic acid sequence is as set forth in SEQ ID NO: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2521 or 2522.

According to some embodiments of the invention, the polynucleotide consists of the nucleic acid sequence selected from the group consisting of SEQ ID NOs: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522.

According to some embodiments of the invention, the nucleic acid sequence encodes an amino acid sequence at least 80% homologous to SEQ ID NO: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2562 or 2563.

According to some embodiments of the invention, the nucleic acid sequence encodes the amino acid sequence selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563.

According to some embodiments of the invention, the nucleic acid sequence is as set forth in SEQ ID NO: 3, 5, 6, 9, 10, 14, 15, 288, 294, 2398-2412 or 2413.

According to some embodiments of the invention, the polynucleotide consists of the nucleic acid sequence selected from the group consisting of SEQ ID NOs: 3, 5, 6, 9, 10, 14, 15, 288, 294, 2398-2413.

According to some embodiments of the invention, the nucleic acid sequence encodes an amino acid sequence at least 80% homologous to SEQ ID NO: 138-153, 1334-1350, 1352-1364, 1458, 1460, 2523-2531 or 2532.

According to some embodiments of the invention, the nucleic acid sequence encodes the amino acid sequence selected from the group consisting of SEQ ID NOs: 138-153, 1334-1350, 1352-1364, 1458, 1460, 2523-2532.

According to some embodiments of the invention, the plant cell forms part of a plant.

According to some embodiments of the invention, the method further comprising growing the plant expressing the exogenous polynucleotide under the abiotic stress.

According to some embodiments of the invention, the abiotic stress is selected from the group consisting of salinity, drought, water deprivation, flood, etiolation, low temperature, high temperature, heavy metal toxicity, anaerobiosis, nutrient deficiency, nutrient excess, atmospheric pollution and UV irradiation.

According to some embodiments of the invention, the yield comprises seed yield or oil yield.

Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the invention, exemplary methods and/or materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and are not intended to be necessarily limiting.

Some embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

In the Drawings:

FIG. 1 is a schematic illustration of the pGI binary plasmid used for expressing the isolated polynucleotide sequences of some embodiments of the invention. RB—T-DNA right border; LB—T-DNA left border; H—HindIII restriction enzyme; X—XbaI restriction enzyme; B—BamHI restriction enzyme; S—SalI restriction enzyme; Sm—SmaI restriction enzyme; R-I—EcoRI restriction enzyme; Sc—SacI/SstI/Ecl136II; (numbers)—Length in base-pairs; NOS pro=nopaline synthase promoter; NPT-II=neomycin phosphotransferase gene; NOS ter=nopaline synthase terminator; Poly-A signal (polyadenylation signal); GUSintron—the GUS reporter gene (coding sequence and intron) The isolated polynucleotide sequences of the invention were cloned into the vector while replacing the GUSintron reporter gene

FIG. 2 is a schematic illustration of the modified pGI binary plasmid used for expressing the isolated polynucleotide sequences of the invention. RB—T-DNA right border; LB—T-DNA left border; MCS—Multiple cloning site; RE—any restriction enzyme; (numbers)—Length in base-pairs; NOS pro=nopaline synthase promoter; NPT-II=neomycin phosphotransferase gene; NOS ter=nopaline synthase terminator; Poly-A signal (polyadenylation signal); GUSintron—the GUS reporter gene (coding sequence and intron) The isolated polynucleotide sequences of the invention were cloned into the vector while replacing the GUSintron reporter gene.

FIGS. 3A-B are images depicting visualization of root development of plants grown in transparent agar plates. The different transgenes were grown in transparent agar plates for 10 days and the plates were photographed every 3-4 days starting at day 1. FIG. 3A —An image of a photograph of plants taken following 10 days on agar plates. FIG. 3B —An image of root analysis in which the length of the root measured is represented by a red arrow.

The present invention, in some embodiments thereof, relates to isolated polynucleotides and polypeptides, expression vectors comprising same and transgenic plants expressing same and, more particularly, but not exclusively, to methods of increasing nitrogen use efficiency, yield, biomass, vigor, growth rate, oil content and abiotic stress tolerance of a plant using same.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details set forth in the following description or exemplified by the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

While reducing the present invention to practice, the present inventors have identified novel polypeptides and polynucleotides which can be used to increase nitrogen use efficiency, fertilizer use efficiency, water use efficiency, yield, growth rate, biomass, oil content, vigor and/or abiotic stress tolerance of a plant.

Thus, as shown in the Examples section which follows, the present inventors have utilized bioinformatics tools to generate digital expression profiles of gene clusters which expression level is associated with various conditions and stresses such as nutrient deficiency, cold, salinity, drought, heat stress, etiolation, waterlogging and oxidative stress (Tables 1-19; Example 1 of the Examples section which follows), and based on the expression profiles have identified genes which are expected to enhance nitrogen use efficiency, biomass, growth rate, yield, vigor, oil content and/or abiotic stress tolerance of a plant (Table 20; polynucleotide SEQ ID NOs:1-137; polypeptides SEQ ID NOs:138-269; Example 1 of the Examples section which follows). Homologous polypeptides and polynucleotides having the same function were also identified (Table 21, polynucleotide SEQ ID NOs:270-1333; polypeptide SEQ ID NOs:1334-2397; Example 2 of the Examples section which follows). To test the effect of the isolated genes on the trait-of-interest, the polynucleotides were cloned into binary vectors (Table 23, polynucleotide SEQ ID NOs: 2398-2522; Example 3 of the Examples section which follows) and the predicted proteins were identified (Table 23, Example 3). Transgenic plants over-expressing the identified polynucleotides were found to exhibit increased nitrogen use efficiency, yield, biomass, photosynthetic areas and growth rate (Tables 24-521 Examples 5, 6 and 7 of the Examples section which follows), as well as increased abiotic stress tolerance (e.g., under salinity stress; Tables 53-55, Example 8 of the Examples section which follows). Altogether, these results suggest the use of the novel polynucleotides and polypeptides of the invention and homologous sequences thereof for increasing nitrogen use efficiency, fertilizer use efficiency, yield (including oil yield, seed yield and oil content), growth rate, biomass, vigor and/or abiotic stress tolerance of a plant.

Thus, according to an aspect of some embodiments of the invention, there is provided method of increasing fertilizer use efficiency, nitrogen use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of a plant, comprising expressing within the plant an exogenous polynucleotide comprising a nucleic acid sequence at least 80% identical to SEQ ID NO: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2521 or 2522, thereby increasing the nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content, water use efficiency and/or abiotic stress tolerance of the plant.

As used herein the phrase “fertilizer use efficiency” refers to the metabolic process(es) which lead to an increase in the plant's yield, biomass, vigor, and growth rate per fertilizer unit applied. The metabolic process can be the uptake, spread, absorbent, accumulation, relocation (within the plant) and use of one or more of the minerals and organic moieties absorbed by the plant, such as nitrogen, phosphates and/or potassium.

As used herein the phrase “fertilizer-limiting conditions” refers to growth conditions which include a level (e.g., concentration) of a fertilizer applied which is below the level needed for normal plant metabolism, growth, reproduction and/or viability.

As used herein the phrase “nitrogen use efficiency (NUE)” refers to the metabolic process(es) which lead to an increase in the plant's yield, biomass, vigor, and growth rate per nitrogen unit applied. The metabolic process can be the uptake, spread, absorbent, accumulation, relocation (within the plant) and use of nitrogen absorbed by the plant.

As used herein the phrase “nitrogen-limiting conditions” refers to growth conditions which include a level (e.g., concentration) of nitrogen (e.g., ammonium or nitrate) applied which is below the level needed for normal plant metabolism, growth, reproduction and/or viability.

Improved plant NUE and FUE is translated in the field into either harvesting similar quantities of yield, while implementing less fertilizers, or increased yields gained by implementing the same levels of fertilizers. Thus, improved NUE or FUE has a direct effect on plant yield in the field. Thus, the polynucleotides and polypeptides of some embodiments of the invention positively affect plant yield, seed yield, and plant biomass. In addition, the benefit of improved plant NUE will certainly improve crop quality and biochemical constituents of the seed such as protein yield and oil yield.

As used herein the phrase “plant yield” refers to the amount (as determined by weight or size) or quantity (numbers) of tissue produced per plant or per growing season. Hence increased yield could affect the economic benefit one can obtain from the plant in a certain growing area and/or growing time.

It should be noted that a plant yield can be affected by various parameters including, but not limited to, plant biomass; plant vigor; growth rate; seed yield; seed or grain quantity; seed or grain quality; oil yield; content of oil, starch and/or protein in harvested organs (e.g., seeds or vegetative parts of the plant); number of flowers (florets) per panicle (expressed as a ratio of number of filled seeds over number of primary panicles); harvest index; number of plants grown per area; number and size of harvested organs per plant and per area; number of plants per growing area (density); number of harvested organs in field; total leaf area; carbon assimilation and carbon partitioning (the distribution/allocation of carbon within the plant); resistance to shade; number of harvestable organs (e.g. seeds), seeds per pod, weight per seed; and modified architecture [such as increase stalk diameter, thickness or improvement of physical properties (e.g. elasticity)].

As used herein the phrase “plant biomass” refers to the amount (measured in grams of air-dry tissue) of a tissue produced from the plant in a growing season, which could also determine or affect the plant yield or the yield per growing area. An increase in plant biomass can be in the whole plant or in parts thereof such as aboveground (harvestable) parts, vegetative biomass, roots and seeds.

As used herein the phrase “growth rate” refers to the increase in plant organ size or mass per time (can be measured in cm 2 per day, day or as the regression coefficient of along time course).

As used herein the phrase “plant vigor” refers to the amount (measured by weight) of tissue produced by the plant in a given time. Hence increased vigor could determine or affect the plant yield or the yield per growing time or growing area. In addition, early vigor (seed and/or seedling) result with improved field stand.

As used herein the phrase “seed yield” refers to the number or weight of the seeds per plant, seeds per pod, or per growing area or to the weight of a single seed, or to the oil extracted per seed. Hence seed yield can be affected by seed dimensions (e.g., length, width, perimeter, area and/or volume), number of (filled) seeds and seed filling rate and by seed oil content. Hence increase seed yield per plant could affect the economic benefit one can obtain from the plant in a certain growing area and/or growing time; and increase seed yield per growing area could be achieved by increasing seed yield per plant, and/or by increasing number of plants grown on the same given area.

The term “seed” (also referred to as “grain” or “kernel”) as used herein refers to a small embryonic plant enclosed in a covering called the seed coat (usually with some stored food), the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant.

The phrase “oil content” as used herein refers to the amount of lipids in a given plant organ, either the seeds (seed oil content) or the vegetative portion of the plant (vegetative oil content) and is typically expressed as percentage of dry weight (10% humidity of seeds) or wet weight (for vegetative portion).

It should be noted that oil content is affected by intrinsic oil production of a tissue (e.g., seed, vegetative portion), as well as the mass or size of the oil-producing tissue per plant or per growth period.

In one embodiment, increase in oil content of the plant can be achieved by increasing the size/mass of a plant's tissue(s) which comprise oil per growth period. Thus, increased oil content of a plant can be achieved by increasing the yield, growth rate, biomass and vigor of the plant.

It should be noted that a plant yield can be determined under stress (e.g., abiotic stress, nitrogen-limiting conditions) or non-stress (normal) conditions.

As used herein, the phrase “non-stress conditions” refers to the growth conditions (e.g., water, temperature, light-dark cycles, humidity, salt concentration, fertilizer concentration in soil, nutrient supply such as nitrogen, phosphorous and/or potassium), which enable normal metabolism, growth, reproduction and/or viability of a plant at any stage in its life cycle (from seed to mature plant and back to seed again). It should be noted that while the non-stress conditions may include some mild variations from the optimal conditions (which vary from one type/species of a plant to another), such variations do not cause the plant to cease growing without the capacity to resume growth.

The phrase “abiotic stress” as used herein refers to any adverse effect on metabolism, growth, reproduction and/or viability of a plant. Accordingly, abiotic stress can be induced by suboptimal environmental growth conditions such as, for example, salinity, water deprivation, flooding, freezing, low or high temperature, heavy metal toxicity, anaerobiosis, nutrient deficiency, atmospheric pollution or UV irradiation. The implications of abiotic stress are discussed in the Background section.

The phrase “abiotic stress tolerance” as used herein refers to the ability of a plant to endure an abiotic stress without suffering a substantial alteration in metabolism, growth, productivity and/or viability.

As used herein the phrase “water use efficiency (WUE)” refers to the level of organic matter produced per unit of water consumed by the plant, i.e., the dry weight of a plant in relation to the plant's water use, e.g., the biomass produced per unit transpiration.

As used herein the term “increasing” refers to at least about 2%, at least about 3%, at least about 4%, at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, increase in nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content, water use efficiency and/or abiotic stress tolerance of a plant as compared to a native plant [i.e., a plant not modified with the biomolecules (polynucleotide or polypeptides) of the invention, e.g., a non-transformed plant of the same species which is grown under the same growth conditions).

As used herein, the phrase “exogenous polynucleotide” refers to a heterologous nucleic acid sequence which may not be naturally expressed within the plant or which overexpression in the plant is desired. The exogenous polynucleotide may be introduced into the plant in a stable or transient manner, so as to produce a ribonucleic acid (RNA) molecule and/or a polypeptide molecule. It should be noted that the exogenous polynucleotide may comprise a nucleic acid sequence which is identical or partially homologous to an endogenous nucleic acid sequence of the plant.

According to some embodiments of the invention the exogenous polynucleotide comprises a nucleic acid sequence which is at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, e.g., 100% identical to the nucleic acid sequence selected from the group consisting of SEQ ID NOs: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522.

Identity (e.g., percent homology) can be determined using any homology comparison software, including for example, the BlastN software of the National Center of Biotechnology Information (NCBI) such as by using default parameters.

According to some embodiments of the invention the exogenous polynucleotide is at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, e.g., 100% identical to the polynucleotide selected from the group consisting of SEQ ID NOs: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522.

According to some embodiments of the invention the exogenous polynucleotide is set forth by SEQ ID NO: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2521 or 2522.

As used herein the term “polynucleotide” refers to a single or double stranded nucleic acid sequence which is isolated and provided in the form of an RNA sequence, a complementary polynucleotide sequence (cDNA), a genomic polynucleotide sequence and/or a composite polynucleotide sequences (e.g., a combination of the above).

The term “isolated” refers to at least partially separated from the natural environment e.g., from a plant cell.

As used herein the phrase “complementary polynucleotide sequence” refers to a sequence, which results from reverse transcription of messenger RNA using a reverse transcriptase or any other RNA dependent DNA polymerase. Such a sequence can be subsequently amplified in vivo or in vitro using a DNA dependent DNA polymerase.

As used herein the phrase “genomic polynucleotide sequence” refers to a sequence derived (isolated) from a chromosome and thus it represents a contiguous portion of a chromosome.

As used herein the phrase “composite polynucleotide sequence” refers to a sequence, which is at least partially complementary and at least partially genomic. A composite sequence can include some exonal sequences required to encode the polypeptide of the present invention, as well as some intronic sequences interposing therebetween. The intronic sequences can be of any source, including of other genes, and typically will include conserved splicing signal sequences. Such intronic sequences may further include cis acting expression regulatory elements.

According to some embodiments of the invention, the exogenous polynucleotide of the invention encodes a polypeptide having an amino acid sequence at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, or more say 100% homologous to the amino acid sequence selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563.

Homology (e.g., percent homology) can be determined using any homology comparison software, including for example, the BlastP or TBLASTN software of the National Center of Biotechnology Information (NCBI) such as by using default parameters, when starting from a polypeptide sequence; or the tBLASTX algorithm (available via the NCBI) such as by using default parameters, which compares the six-frame conceptual translation products of a nucleotide query sequence (both strands) against a protein sequence database.

Homologous sequences include both orthologous and paralogous sequences. The term “paralogous” relates to gene-duplications within the genome of a species leading to paralogous genes. The term “orthologous” relates to homologous genes in different organisms due to ancestral relationship.

One option to identify orthologues in monocot plant species is by performing a reciprocal blast search. This may be done by a first blast involving blasting the sequence-of-interest against any sequence database, such as the publicly available NCBI database which may be found at: Hypertext Transfer Protocol://World Wide Web (dot) ncbi (dot) nlm (dot) nih (dot) gov. If orthologues in rice were sought, the sequence-of-interest would be blasted against, for example, the 28,469 full-length cDNA clones from Oryza sativa Nipponbare available at NCBI. The blast results may be filtered. The full-length sequences of either the filtered results or the non-filtered results are then blasted back (second blast) against the sequences of the organism from which the sequence-of-interest is derived. The results of the first and second blasts are then compared. An orthologue is identified when the sequence resulting in the highest score (best hit) in the first blast identifies in the second blast the query sequence (the original sequence-of-interest) as the best hit. Using the same rational a paralogue (homolog to a gene in the same organism) is found. In case of large sequence families, the ClustalW program may be used [Hypertext Transfer Protocol://World Wide Web (dot) ebi (dot) ac (dot) uk/Tools/clustalw2/index (dot) html], followed by a neighbor-joining tree (Hypertext Transfer Protocol://en (dot) wikipedia (dot) org/wiki/Neighbor-joining) which helps visualizing the clustering.

According to some embodiments of the invention, the exogenous polynucleotide encodes a polypeptide consisting of the amino acid sequence set forth by SEQ ID NO: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2562 or 2563.

According to an aspect of some embodiments of the invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of a plant. The method is effected by expressing within the plant an exogenous polynucleotide. comprising the nucleic acid sequence selected from the group consisting of SEQ ID NOs: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522, 3, 5, 6, 9, 10, 14, 15, 20, 61, 62, 129, 288, 294, 307, 363, 667, 668, 669, 670, 672, 2398-2413, 2456 and 2457, thereby increasing the nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of the plant.

According to some embodiments of the invention the exogenous polynucleotide is set forth by SEQ ID NO: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522, 3, 5, 6, 9, 10, 14, 15, 20, 61, 62, 129, 288, 294, 307, 363, 667, 668, 669, 670, 672, 2398-2413, 2456 or 2457.

According to some embodiments of the invention, the exogenous polynucleotide of the invention encodes a polypeptide having an amino acid sequence selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563, 138-143, 146, 148, 150-152, 157, 162, 198, 265, 1334-1350, 1352-1364, 1426-1428, 1458, 1460, 1732-1734, 1737-1738, 2523-2532, 2542 and 2543, thereby increasing the nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content and/or abiotic stress tolerance of the plant.

According to an aspect of some embodiments of the invention there is provided a method of increasing nitrogen use efficiency, fertilizer use efficiency and/or oil content of a plant. The method is effected by expressing within the plant an exogenous polynucleotide comprising a nucleic acid sequence at least 80% identical to SEQ ID NO: 3, 5, 6, 9, 10, 14, 15, 288, 294, 2398-2412 or 2413, thereby increasing the nitrogen use efficiency, fertilizer use efficiency, and/or oil content of the plant.

According to some embodiments of the invention the exogenous polynucleotide comprises a nucleic acid sequence which is at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, e.g., 100% identical to the nucleic acid sequence selected from the group consisting of SEQ ID NOs: 3, 5, 6, 9, 10, 14, 15, 288, 294, 2398-2413.

According to some embodiments of the invention the exogenous polynucleotide is at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, e.g., 100% identical to the polynucleotide selected from the group consisting of SEQ ID NOs: 3, 5, 6, 9, 10, 14, 15, 288, 294, 2398-2413.

According to some embodiments of the invention the exogenous polynucleotide is set forth by SEQ ID NO: 3, 5, 6, 9, 10, 14, 15, 288, 294, 2398-2412 or 2413.

According to some embodiments of the invention, the exogenous polynucleotide of the invention encodes a polypeptide having an amino acid sequence at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, or more say 100% homologous to the amino acid sequence selected from the group consisting of SEQ ID NOs: 138-153, 1334-1350, 1352-1364, 1458, 1460, 2523-2532.

According to some embodiments of the invention, the exogenous polynucleotide encodes a polypeptide consisting of the amino acid sequence set forth by SEQ ID NO: 138-153, 1334-1350, 1352-1364, 1458, 1460, 2523-2531 or 2532.

Nucleic acid sequences encoding the polypeptides of the present invention may be optimized for expression. Non-limiting examples of optimized nucleic acid sequences are provided in SEQ ID NOs: 2415, 2420, 2428, 2430, 2431, 2436, 2437, 2441, 2444, 2445, 2446, 2451, 2456, 2468, 2471, 2478, 2481, 2484, 2520 and 2522 (Table 23). Examples of such sequence modifications include, but are not limited to, an altered G/C content to more closely approach that typically found in the plant species of interest, and the removal of codons atypically found in the plant species commonly referred to as codon optimization.

The phrase “codon optimization” refers to the selection of appropriate DNA nucleotides for use within a structural gene or fragment thereof that approaches codon usage within the plant of interest. Therefore, an optimized gene or nucleic acid sequence refers to a gene in which the nucleotide sequence of a native or naturally occurring gene has been modified in order to utilize statistically-preferred or statistically-favored codons within the plant. The nucleotide sequence typically is examined at the DNA level and the coding region optimized for expression in the plant species determined using any suitable procedure, for example as described in Sardana et al. (1996, Plant Cell Reports 15:677-681). In this method, the standard deviation of codon usage, a measure of codon usage bias, may be calculated by first finding the squared proportional deviation of usage of each codon of the native gene relative to that of highly expressed plant genes, followed by a calculation of the average squared deviation. The formula used is: 1 SDCU=n=1 N[(Xn−Yn)/Yn]2/N, where Xn refers to the frequency of usage of codon n in highly expressed plant genes, where Yn to the frequency of usage of codon n in the gene of interest and N refers to the total number of codons in the gene of interest. A Table of codon usage from highly expressed genes of dicotyledonous plants is compiled using the data of Murray et al. (1989, Nuc Acids Res. 17:477-498).

One method of optimizing the nucleic acid sequence in accordance with the preferred codon usage for a particular plant cell type is based on the direct use, without performing any extra statistical calculations, of codon optimization Tables such as those provided on-line at the Codon Usage Database through the NIAS (National Institute of Agrobiological Sciences) DNA bank in Japan (Hypertext Transfer Protocol://World Wide Web (dot) kazusa (dot) or (dot) jp/codon/). The Codon Usage Database contains codon usage tables for a number of different species, with each codon usage Table having been statistically determined based on the data present in Genbank.

By using the above Tables to determine the most preferred or most favored codons for each amino acid in a particular species (for example, rice), a naturally-occurring nucleotide sequence encoding a protein of interest can be codon optimized for that particular plant species. This is effected by replacing codons that may have a low statistical incidence in the particular species genome with corresponding codons, in regard to an amino acid, that are statistically more favored. However, one or more less-favored codons may be selected to delete existing restriction sites, to create new ones at potentially useful junctions (5′ and 3′ ends to add signal peptide or termination cassettes, internal sites that might be used to cut and splice segments together to produce a correct full-length sequence), or to eliminate nucleotide sequences that may negatively effect mRNA stability or expression.

The naturally-occurring encoding nucleotide sequence may already, in advance of any modification, contain a number of codons that correspond to a statistically-favored codon in a particular plant species. Therefore, codon optimization of the native nucleotide sequence may comprise determining which codons, within the native nucleotide sequence, are not statistically-favored with regards to a particular plant, and modifying these codons in accordance with a codon usage table of the particular plant to produce a codon optimized derivative. A modified nucleotide sequence may be fully or partially optimized for plant codon usage provided that the protein encoded by the modified nucleotide sequence is produced at a level higher than the protein encoded by the corresponding naturally occurring or native gene. Construction of synthetic genes by altering the codon usage is described in for example PCT Patent Application 93/07278.

According to some embodiments of the invention, the exogenous polynucleotide is a non-coding RNA.

As used herein the phrase ‘non-coding RNA” refers to an RNA molecule which does not encode an amino acid sequence (a polypeptide). Examples of such non-coding RNA molecules include, but are not limited to, an antisense RNA, a pre-miRNA (precursor of a microRNA), or a precursor of a Piwi-interacting RNA (piRNA).

According to a specific embodiment the non-coding polynucleotide comprises the nucleic acid sequence of SEQ ID NO: 64 or 2459 (NUE512).

Thus, the invention encompasses nucleic acid sequences described hereinabove; fragments thereof, sequences hybridizable therewith, sequences homologous thereto, sequences encoding similar polypeptides with different codon usage, altered sequences characterized by mutations, such as deletion, insertion or substitution of one or more nucleotides, either naturally occurring or man induced, either randomly or in a targeted fashion.

The invention provides an isolated polynucleotide comprising a nucleic acid sequence at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, e.g., 100% identical to the polynucleotide selected from the group consisting of SEQ ID NOs: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522.

According to some embodiments of the invention the nucleic acid sequence is capable of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content, abiotic stress tolerance and/or water use efficiency of a plant.

According to some embodiments of the invention the isolated polynucleotide comprising the nucleic acid sequence selected from the group consisting of SEQ ID NOs: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522, 3, 5, 6, 9, 10, 14, 15, 20, 61, 62, 129, 288, 294, 307, 363, 667, 668, 669, 670, 672, 2398-2413, 2456 and 2457.

According to some embodiments of the invention the isolated polynucleotide is set forth by SEQ ID NO: 2506, 2512, 2442, 2496, 2446, 1, 2, 4, 7, 8, 11, 12, 13, 16-19, 21-60, 63-128, 130-137, 270-287, 289-293, 295-306, 308-362, 364-666, 671, 673-1333, 2414-2441, 2443-2445, 2447-2455, 2458-2495, 2497-2505, 2507-2511, 2513-2522, 3, 5, 6, 9, 10, 14, 15, 20, 61, 62, 129, 288, 294, 307, 363, 667, 668, 669, 670, 672, 2398-2413, 2456 or 2457.

The invention provides an isolated polynucleotide comprising a nucleic acid sequence encoding a polypeptide which comprises an amino acid sequence at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, or more say 100% homologous to the amino acid sequence selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563.

According to some embodiments of the invention the amino acid sequence is capable of increasing nitrogen use efficiency, fertilizer use efficiency, yield, growth rate, vigor, biomass, oil content, abiotic stress tolerance and/or water use efficiency of a plant.

The invention provides an isolated polynucleotide comprising a nucleic acid sequence encoding a polypeptide which comprises the amino acid sequence selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563, 138-143, 146, 148, 150-152, 157, 162, 198, 265, 1334-1350, 1352-1364, 1426-1428, 1458, 1460, 1732-1734, 1737-1738, 2523-2532, 2542 and 2543.

The invention provides an isolated polypeptide comprising an amino acid sequence at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, or more say 100% homologous to an amino acid sequence selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563.

According to some embodiments of the invention, the polypeptide comprising an amino acid sequence selected from the group consisting of SEQ ID NOs: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563, 138-143, 146, 148, 150-152, 157, 162, 198, 265, 1334-1350, 1352-1364, 1426-1428, 1458, 1460, 1732-1734, 1737-1738, 2523-2532, 2542 and 2543.

According to some embodiments of the invention, the polypeptide is set forth by SEQ ID NO: 2557, 2560, 184, 238, 188, 154-156, 158-161, 163-183, 185-187, 189-197, 200-237, 239-264, 266-269, 1351, 1365-1425, 1429-1457, 1459, 1461-1730, 1735, 1739-2397, 2533-2541, 2544-2556, 2558, 2559, 2561-2563, 138-143, 146, 148, 150-152, 157, 162, 198, 265, 1334-1350, 1352-1364, 1426-1428, 1458, 1460, 1732-1734, 1737-1738, 2523-2532, 2542 or 2543.

The invention also encompasses fragments of the above described polypeptides and polypeptides having mutations, such as deletions, insertions or substitutions of one or more amino acids, either naturally occurring or man induced, either randomly or in a targeted fashion.

The term “plant” as used herein encompasses whole plants, ancestors and progeny of the plants and plant parts, including seeds, shoots, stems, roots (including tubers), and plant cells, tissues and organs. The plant may be in any form including suspension cultures, embryos, meristematic regions, callus tissue, leaves, gametophytes, sporophytes, pollen, and microspores. Plants that are particularly useful in the methods of the invention include all plants which belong to the superfamily Viridiplantae, in particular monocotyledonous and dicotyledonous plants including a fodder or forage legume, ornamental plant, food crop, tree, or shrub selected from the list comprising Acacia spp., Acer spp., Actinidia spp., Aesculus spp., Agathis australis, Albizia amara, Alsophila tricolor, Andropogon spp., Arachis spp, Areca catechu, Astelia fragrans, Astragalus cicer, Baikiaea plurijuga, Betula spp., Brassica spp., Bruguiera gymnorrhiza, Burkea africana, Butea frondosa, Cadaba farinosa, Calliandra spp, Camellia sinensis, Canna indica, Capsicum spp., Cassia spp., Centroema pubescens, Chacoomeles spp., Cinnamomum cassia, Coffea arabica, Colophospermum mopane, Coronillia varia, Cotoneaster serotina, Crataegus spp., Cucumis spp., Cupressus spp., Cyathea dealbata, Cydonia oblonga, Cryptomeria japonica, Cymbopogon spp., Cynthea dealbata, Cydonia oblonga, Dalbergia monetaria, Davallia divaricata, Desmodium spp., Dicksonia squarosa, Dibeteropogon amplectens, Dioclea spp, Dolichos spp., Dorycnium rectum, Echinochloa pyramidalis, Ehraffia spp., Eleusine coracana, Eragrestis spp., Erythrina spp., Eucalypfus spp., Euclea schimperi, Eulalia vi/losa, Pagopyrum spp., Feijoa sellowlana, Fragaria spp., Flemingia spp, Freycinetia banksli, Geranium thunbergii, GinAgo biloba, Glycine javanica, Gliricidia spp, Gossypium hirsutum, Grevillea spp., Guibourtia coleosperma, Hedysarum spp., Hemaffhia altissima, Heteropogon contoffus, Hordeum vulgare, Hyparrhenia rufa, Hypericum erectum, Hypeffhelia dissolute, Indigo incamata, Iris spp., Leptarrhena pyrolifolia, Lespediza spp., Lettuca spp., Leucaena leucocephala, Loudetia simplex, Lotonus bainesli, Lotus spp., Macrotyloma axillare, Malus spp., Manihot esculenta, Medicago saliva, Metasequoia glyptostroboides, Musa sapientum, Nicotianum spp., Onobrychis spp., Ornithopus spp., Oryza spp., Peltophorum africanum, Pennisetum spp., Persea gratissima, Petunia spp., Phaseolus spp., Phoenix canariensis, Phormium cookianum, Photinia spp., Picea glauca, Pinus spp., Pisum sativam, Podocarpus totara, Pogonarthria fleckii, Pogonaffhria squarrosa, Populus spp., Prosopis cineraria, Pseudotsuga menziesii, Pterolobium stellatum, Pyrus communis, Quercus spp., Rhaphiolepsis umbellata, Rhopalostylis sapida, Rhus natalensis, Ribes grossularia, Ribes spp., Robinia pseudoacacia, Rosa spp., Rubus spp., Salix spp., Schyzachyrium sanguineum, Sciadopitys vefficillata, Sequoia sempervirens, Sequoiadendron giganteum, Sorghum bicolor, Spinacia spp., Sporobolus fimbriatus, Stiburus alopecuroides, Stylosanthos humilis, Tadehagi spp, Taxodium distichum, Themeda triandra, Trifolium spp., Triticum spp., Tsuga heterophylla, Vaccinium spp., Vicia spp., Vitis vinifera, Watsonia pyramidata, Zantedeschia aethiopica, Zea mays, amaranth, artichoke, asparagus, broccoli, Brussels sprouts, cabbage, canola, carrot, cauliflower, celery, collard greens, flax, kale, lentil, oilseed rape, okra, onion, potato, rice, soybean, straw, sugar beet, sugar cane, sunflower, tomato, squash tea, maize, wheat, barely, rye, oat, peanut, pea, lentil and alfalfa, cotton, rapeseed, canola, pepper, sunflower, tobacco, eggplant, eucalyptus , a tree, an ornamental plant, a perennial grass and a forage crop. Alternatively algae and other non-Viridiplantae can be used for the methods of the present invention.

According to some embodiments of the invention, the plant used by the method of the invention is a crop plant such as rice, maize, wheat, barley, peanut, potato, sesame, olive tree, palm oil, banana, soybean, sunflower, canola, sugarcane, alfalfa, millet, leguminosae (bean, pea), flax, lupinus , rapeseed, tobacco, poplar and cotton.

According to some embodiments of the invention, there is provided a plant cell exogenously expressing the polynucleotide of some embodiments of the invention, the nucleic acid construct of some embodiments of the invention and/or the polypeptide of some embodiments of the invention.

According to some embodiments of the invention, expressing the exogenous polynucleotide of the invention within the plant is effected by transforming one or more cells of the plant with the exogenous polynucleotide, followed by generating a mature plant from the transformed cells and cultivating the mature plant under conditions suitable for expressing the exogenous polynucleotide within the mature plant.

According to some embodiments of the invention, the transformation is effected by introducing to the plant cell a nucleic acid construct which includes the exogenous polynucleotide of some embodiments of the invention and at least one promoter for directing transcription of the exogenous polynucleotide in a host cell (a plant cell). Further details of suitable transformation approaches are provided hereinbelow.

According to some embodiments of the invention, there is provided a nucleic acid construct comprising the isolated polynucleotide of the invention, and a promoter for directing transcription of the nucleic acid sequence of the isolated polynucleotide in a host cell.

According to some embodiments of the invention, the isolated polynucleotide is operably linked to the promoter sequence.

A coding nucleic acid sequence is “operably linked” to a regulatory sequence (e.g., promoter) if the regulatory sequence is capable of exerting a regulatory effect on the coding sequence linked thereto.

As used herein, the term “promoter” refers to a region of DNA which lies upstream of the transcriptional initiation site of a gene to which RNA polymerase binds to initiate transcription of RNA. The promoter controls where (e.g., which portion of a plant) and/or when (e.g., at which stage or condition in the lifetime of an organism) the gene is expressed.

Any suitable promoter sequence can be used by the nucleic acid construct of the present invention. Preferably the promoter is a constitutive promoter, a tissue-specific, or an abiotic stress-inducible promoter.

Suitable constitutive promoters include, for example, CaMV 35S promoter (SEQ ID NO: 3063; Odell et al., Nature 313:810-812, 1985); Arabidopsis At6669 promoter (SEQ ID NO:3064; see PCT Publication No. WO04081173A2); maize Ubi 1 (Christensen et al., Plant Sol. Biol. 18:675-689, 1992); rice actin (McElroy et al., Plant Cell 2:163-171, 1990); pEMU (Last et al., Theor. Appl. Genet. 81:581-588, 1991); CaMV 19S (Nilsson et al., Physiol. Plant 100:456-462, 1997); GOS2 (de Pater et al, Plant J November; 2(6):837-44, 1992); ubiquitin (Christensen et al, Plant Mol. Biol. 18: 675-689, 1992); Rice cyclophilin (Bucholz et al, Plant Mol Biol. 25(5):837-43, 1994); Maize H3 histone (Lepetit et al, Mol. Gen. Genet. 231: 276-285, 1992); Actin 2 (An et al, Plant J. 10(1); 107-121, 1996) and Synthetic Super MAS (Ni et al., The Plant Journal 7: 661-76, 1995). Other constitutive promoters include those in U.S. Pat. Nos. 5,659,026, 5,608,149; 5,608,144; 5,604,121; 5,569,597; 5,466,785; 5,399,680; 5,268,463; and 5,608,142.

Suitable tissue-specific promoters include, but not limited to, leaf-specific promoters [such as described, for example, by Yamamoto et al., Plant J. 12:255-265, 1997; Kwon et al., Plant Physiol. 105:357-67, 1994; Yamamoto et al., Plant Cell Physiol. 35:773-778, 1994; Gotor et al., Plant J. 3:509-18, 1993; Orozco et al., Plant Mol. Biol. 23:1129-1138, 1993; and Matsuoka et al., Proc. Natl. Acad. Sci. USA 90:9586-9590, 1993], seed-preferred promoters [e.g., from seed specific genes (Simon, et al., Plant Mol. Biol. 5. 191, 1985; Scofield, et al., J. Biol. Chem. 262: 12202, 1987; Baszczynski, et al., Plant Mol. Biol. 14: 633, 1990), Brazil Nut albumin (Pearson' et al., Plant Mol. Biol. 18: 235-245, 1992), legumin (Ellis, et al. Plant Mol. Biol. 10: 203-214, 1988), Glutelin (rice) (Takaiwa, et al., Mol. Gen. Genet. 208: 15-22, 1986; Takaiwa, et al., FEBS Letts. 221: 43-47, 1987), Zein (Matzke et al Plant Mol Biol, 143). 323-32 1990), napA (Stalberg, et al, Planta 199: 515-519, 1996), Wheat SPA (Albani et al, Plant Cell, 9: 171-184, 1997), sunflower oleosin (Cummins, etal., Plant Mol. Biol. 19: 873-876, 1992)], endosperm specific promoters [e.g., wheat LMW and HMW, glutenin-1 (Mol Gen Genet 216:81-90, 1989; NAR 17:461-2), wheat a, b and g gliadins (EMBO3:1409-15, 1984), Barley ltrl promoter, barley B1, C, D hordein (Theor Appl Gen 98:1253-62, 1999; Plant J 4:343-55, 1993; Mol Gen Genet 250:750-60, 1996), Barley DOF (Mena et al, The Plant Journal, 116(1): 53-62, 1998), Biz2 (EP99106056.7), Synthetic promoter (Vicente-Carbajosa et al., Plant J. 13: 629-640, 1998), rice prolamin NRP33, rice-globulin Glb-1 (Wu et al, Plant Cell Physiology 39(8) 885-889, 1998), rice alpha-globulin REB/OHP-1 (Nakase et al. Plant Mol. Biol. 33: 513-S22, 1997), rice ADP-glucose PP (Trans Res 6:157-68, 1997), maize ESR gene family (Plant J 12:235-46, 1997), sorgum gamma-kafirin (PMB 32:1029-35, 1996)], embryo specific promoters [e.g., rice OSH1 (Sato et al, Proc. Nati. Acad. Sci. USA, 93: 8117-8122), KNOX (Postma-Haarsma of al, Plant Mol. Biol. 39:257-71, 1999), rice oleosin (Wu et at, J. Biochem., 123:386, 1998)], and flower-specific promoters [e.g., AtPRP4, chalene synthase (chsA) (Van der Meer, et al., Plant Mol. Biol. 15, 95-109, 1990), LAT52 (Twell et al Mol. Gen Genet. 217:240-245; 1989), apetala -3].

Suitable abiotic stress-inducible promoters include, but not limited to, salt-inducible promoters such as RD29A (Yamaguchi-Shinozalei et al., Mol. Gen. Genet. 236:331-340, 1993); drought-inducible promoters such as maize rab17 gene promoter (Pla et. al., Plant Mol. Biol. 21:259-266, 1993), maize rab28 gene promoter (Busk et. al., Plant J. 11:1285-1295, 1997) and maize Ivr2 gene promoter (Pelleschi et. al., Plant Mol. Biol. 39:373-380, 1999); heat-inducible promoters such as heat tomato hsp80-promoter from tomato (U.S. Pat. No. 5,187,267).

The nucleic acid construct of some embodiments of the invention can further include an appropriate selectable marker and/or an origin of replication. According to some embodiments of the invention, the nucleic acid construct utilized is a shuttle vector, which can propagate both in E. coli (wherein the construct comprises an appropriate selectable marker and origin of replication) and be compatible with propagation in cells. The construct according to the present invention can be, for example, a plasmid, a bacmid, a phagemid, a cosmid, a phage, a virus or an artificial chromosome.

The nucleic acid construct of some embodiments of the invention can be utilized to stably or transiently transform plant cells. In stable transformation, the exogenous polynucleotide is integrated into the plant genome and as such it represents a stable and inherited trait. In transient transformation, the exogenous polynucleotide is expressed by the cell transformed but it is not integrated into the genome and as such it represents a transient trait.

There are various methods of introducing foreign genes into both monocotyledonous and dicotyledonous plants (Potrykus, I., Annu. Rev. Plant. Physiol, Plant. Mol. Biol. (1991) 42:205-225; Shimamoto et al, Nature (1989) 338:274-276).

The principle methods of causing stable integration of exogenous DNA into plant genomic DNA include two main approaches:

(i) Agrobacterium -mediated gene transfer: Klee et al. (1987) Annu. Rev. Plant Physiol. 38:467-486; Klee and Rogers in Cell Culture and Somatic Cell Genetics of Plants, Vol. 6, Molecular Biology of Plant Nuclear Genes, eds. Schell, J., and Vasil, L. K., Academic Publishers, San Diego, Calif. (1989) p. 2-25; Gatenby, in Plant Biotechnology, eds. Kung, S. and Arntzen, C. J., Butterworth Publishers, Boston, Mass. (1989) p. 93-112.

(ii) Direct DNA uptake: Paszkowski et al., in Cell Culture and Somatic Cell Genetics of Plants, Vol. 6, Molecular Biology of Plant Nuclear Genes eds. Schell, J., and Vasil, L. K., Academic Publishers, San Diego, Calif. (1989) p. 52-68; including methods for direct uptake of DNA into protoplasts, Toriyama, K. et al. (1988) Bio/Technology 6:1072-1074. DNA uptake induced by brief electric shock of plant cells: Zhang et al. Plant Cell Rep. (1988) 7:379-384. Fromm et al. Nature (1986) 319:791-793. DNA injection into plant cells or tissues by particle bombardment, Klein et al. Bio/Technology (1988) 6:559-563; McCabe et al. Bio/Technology (1988) 6:923-926; Sanford, Physiol. Plant. (1990) 79:206-209; by the use of micropipette systems: Neuhaus et al., Theor. Appl. Genet. (1987) 75:30-36; Neuhaus and Spangenberg, Physiol. Plant. (1990) 79:213-217; glass fibers or silicon carbide whisker transformation of cell cultures, embryos or callus tissue, U.S. Pat. No. 5,464,765 or by the direct incubation of DNA with germinating pollen, DeWet et al. in Experimental Manipulation of Ovule Tissue, eds. Chapman, G. P. and Mantell, S. H. and Daniels, W. Longman, London, (1985) p. 197-209; and Ohta, Proc. Natl. Acad. Sci. USA (1986) 83:715-719.

The Agrobacterium system includes the use of plasmid vectors that contain defined DNA segments that integrate into the plant genomic DNA. Methods of inoculation of the plant tissue vary depending upon the plant species and the Agrobacterium delivery system. A widely used approach is the leaf disc procedure which can be performed with any tissue explant that provides a good source for initiation of whole plant differentiation. See, e.g., Horsch et al. in Plant Molecular Biology Manual A5, Kluwer Academic Publishers, Dordrecht (1988) p. 1-9. A supplementary approach employs the Agrobacterium delivery system in combination with vacuum infiltration. The Agrobacterium system is especially viable in the creation of transgenic dicotyledonous plants.

There are various methods of direct DNA transfer into plant cells. In electroporation, the protoplasts are briefly exposed to a strong electric field. In microinjection, the DNA is mechanically injected directly into the cells using very small micropipettes. In microparticle bombardment, the DNA is adsorbed on microprojectiles such as magnesium sulfate crystals or tungsten particles, and the microprojectiles are physically accelerated into cells or plant tissues.

Following stable transformation plant propagation is exercised. The most common method of plant propagation is by seed. Regeneration by seed propagation, however, has the deficiency that due to heterozygosity there is a lack of uniformity in the crop, since seeds are produced by plants according to the genetic variances governed by Mendelian rules. Basically, each seed is genetically different and each will grow with its own specific traits. Therefore, it is preferred that the transformed plant be produced such that the regenerated plant has the identical traits and characteristics of the parent transgenic plant. Therefore, it is preferred that the transformed plant be regenerated by micropropagation which provides a rapid, consistent reproduction of the transformed plants.

Micropropagation is a process of growing new generation plants from a single piece of tissue that has been excised from a selected parent plant or cultivar. This process permits the mass reproduction of plants having the preferred tissue expressing the fusion protein. The new generation plants which are produced are genetically identical to, and have all of the characteristics of, the original plant. Micropropagation allows mass production of quality plant material in a short period of time and offers a rapid multiplication of selected cultivars in the preservation of the characteristics of the original transgenic or transformed plant. The advantages of cloning plants are the speed of plant multiplication and the quality and uniformity of plants produced.

Micropropagation is a multi-stage procedure that requires alteration of culture medium or growth conditions between stages. Thus, the micropropagation process involves four basic stages: Stage one, initial tissue culturing; stage two, tissue culture multiplication; stage three, differentiation and plant formation; and stage four, greenhouse culturing and hardening. During stage one, initial tissue culturing, the tissue culture is established and certified contaminant-free. During stage two, the initial tissue culture is multiplied until a sufficient number of tissue samples are produced to meet production goals. During stage three, the tissue samples grown in stage two are divided and grown into individual plantlets. At stage four, the transformed plantlets are transferred to a greenhouse for hardening where the plants' tolerance to light is gradually increased so that it can be grown in the natural environment.

According to some embodiments of the invention, the transgenic plants are generated by transient transformation of leaf cells, meristematic cells or the whole plant.

Transient transformation can be effected by any of the direct DNA transfer methods described above or by viral infection using modified plant viruses.

Viruses that have been shown to be useful for the transformation of plant hosts include CaMV, Tobacco mosaic virus (TMV), brome mosaic virus (BMV) and Bean Common Mosaic Virus (BV or BCMV). Transformation of plants using plant viruses is described in U.S. Pat. No. 4,855,237 (bean golden mosaic virus; BGV), EP-A 67,553 (TMV), Japanese Published Application No. 63-14693 (TMV), EPA 194,809 (BV), EPA 278,667 (BV); and Gluzman, Y. et al., Communications in Molecular Biology: Viral Vectors, Cold Spring Harbor Laboratory, New York, pp. 172-189 (1988). Pseudovirus particles for use in expressing foreign DNA in many hosts, including plants are described in WO 87/06261.

According to some embodiments of the invention, the virus used for transient transformations is avirulent and thus is incapable of causing severe symptoms such as reduced growth rate, mosaic, ring spots, leaf roll, yellowing, streaking, pox formation, tumor formation and pitting. A suitable avirulent virus may be a naturally occurring avirulent virus or an artificially attenuated virus. Virus attenuation may be effected by using methods well known in the art including, but not limited to, sub-lethal heating, chemical treatment or by directed mutagenesis techniques such as described, for example, by Kurihara and Watanabe (Molecular Plant Pathology 4:259-269, 2003), Gal-on et al. (1992), Atreya et al. (1992) and Huet et al. (1994).

Suitable virus strains can be obtained from available sources such as, for example, the American Type culture Collection (ATCC) or by isolation from infected plants. Isolation of viruses from infected plant tissues can be effected by techniques well known in the art such as described, for example by Foster and Tatlor, Eds. “Plant Virology Protocols: From Virus Isolation to Transgenic Resistance (Methods in Molecular Biology (Humana Pr), Vol 81)”, Humana Press, 1998. Briefly, tissues of an infected plant believed to contain a high concentration of a suitable virus, preferably young leaves and flower petals, are ground in a buffer solution (e.g., phosphate buffer solution) to produce a virus infected sap which can be used in subsequent inoculations.

Construction of plant RNA viruses for the introduction and expression of non-viral exogenous polynucleotide sequences in plants is demonstrated by the above references as well as by Dawson, W. O. et al., Virology (1989) 172:285-292; Takamatsu et al. EMBO J. (1987) 6:307-311; French et al. Science (1986) 231:1294-1297; Takamatsu et al. FEBS Letters (1990) 269:73-76; and U.S. Pat. No. 5,316,931.

When the virus is a DNA virus, suitable modifications can be made to the virus itself. Alternatively, the virus can first be cloned into a bacterial plasmid for ease of constructing the desired viral vector with the foreign DNA. The virus can then be excised from the plasmid. If the virus is a DNA virus, a bacterial origin of replication can be attached to the viral DNA, which is then replicated by the bacteria. Transcription and translation of this DNA will produce the coat protein which will encapsidate the viral DNA. If the virus is an RNA virus, the virus is generally cloned as a cDNA and inserted into a plasmid. The plasmid is then used to make all of the constructions. The RNA virus is then produced by transcribing the viral sequence of the plasmid and translation of the viral genes to produce the coat protein(s) which encapsidate the viral RNA.

In one embodiment, a plant viral polynucleotide is provided in which the native coat protein coding sequence has been deleted from a viral polynucleotide, a non-native plant viral coat protein coding sequence and a non-native promoter, preferably the subgenomic promoter of the non-native coat protein coding sequence, capable of expression in the plant host, packaging of the recombinant plant viral polynucleotide, and ensuring a systemic infection of the host by the recombinant plant viral polynucleotide, has been inserted. Alternatively, the coat protein gene may be inactivated by insertion of the non-native polynucleotide sequence within it, such that a protein is produced. The recombinant plant viral polynucleotide may contain one or more additional non-native subgenomic promoters. Each non-native subgenomic promoter is capable of transcribing or expressing adjacent genes or polynucleotide sequences in the plant host and incapable of recombination with each other and with native subgenomic promoters. Non-native (foreign) polynucleotide sequences may be inserted adjacent the native plant viral subgenomic promoter or the native and a non-native plant viral subgenomic promoters if more than one polynucleotide sequence is included. The non-native polynucleotide sequences are transcribed or expressed in the host plant under control of the subgenomic promoter to produce the desired products.

In a second embodiment, a recombinant plant viral polynucleotide is provided as in the first embodiment except that the native coat protein coding sequence is placed adjacent one of the non-native coat protein subgenomic promoters instead of a non-native coat protein coding sequence.

In a third embodiment, a recombinant plant viral polynucleotide is provided in which the native coat protein gene is adjacent its subgenomic promoter and one or more non-native subgenomic promoters have been inserted into the viral polynucleotide. The inserted non-native subgenomic promoters are capable of transcribing or expressing adjacent genes in a plant host and are incapable of recombination with each other and with native subgenomic promoters. Non-native polynucleotide sequences may be inserted adjacent the non-native subgenomic plant viral promoters such that the sequences are transcribed or expressed in the host plant under control of the subgenomic promoters to produce the desired product.

In a fourth embodiment, a recombinant plant viral polynucleotide is provided as in the third embodiment except that the native coat protein coding sequence is replaced by a non-native coat protein coding sequence.

The viral vectors are encapsidated by the coat proteins encoded by the recombinant plant viral polynucleotide to produce a recombinant plant virus. The recombinant plant viral polynucleotide or recombinant plant virus is used to infect appropriate host plants. The recombinant plant viral polynucleotide is capable of replication in the host, systemic spread in the host, and transcription or expression of foreign gene(s) (exogenous polynucleotide) in the host to produce the desired protein.

Techniques for inoculation of viruses to plants may be found in Foster and Taylor, eds. “Plant Virology Protocols: From Virus Isolation to Transgenic Resistance (Methods in Molecular Biology (Humana Pr), Vol 81)”, Humana Press, 1998; Maramorosh and Koprowski, eds. “Methods in Virology” 7 vols, Academic Press, New York 1967-1984; Hill, S. A. “Methods in Plant Virology”, Blackwell, Oxford, 1984; Walkey, D. G. A. “Applied Plant Virology”, Wiley, New York, 1985; and Kado and Agrawa, eds. “Principles and Techniques in Plant Virology”, Van Nostrand-Reinhold, New York.

In addition to the above, the polynucleotide of the present invention can also be introduced into a chloroplast genome thereby enabling chloroplast expression.

A technique for introducing exogenous polynucleotide sequences to the genome of the chloroplasts is known. This technique involves the following procedures. First, plant cells are chemically treated so as to reduce the number of chloroplasts per cell to about one. Then, the exogenous polynucleotide is introduced via particle bombardment into the cells with the aim of introducing at least one exogenous polynucleotide molecule into the chloroplasts. The exogenous polynucleotides selected such that it is integratable into the chloroplast's genome via homologous recombination which is readily effected by enzymes inherent to the chloroplast. To this end, the exogenous polynucleotide includes, in addition to a gene of interest, at least one polynucleotide stretch which is derived from the chloroplast's genome. In addition, the exogenous polynucleotide includes a selectable marker, which serves by sequential selection procedures to ascertain that all or substantially all of the copies of the chloroplast genomes following such selection will include the exogenous polynucleotide. Further details relating to this technique are found in U.S. Pat. Nos. 4,945,050; and 5,693,507 which are incorporated herein by reference. A polypeptide can thus be produced by the protein expression system of the chloroplast and become integrated into the chloroplast's inner membrane.

Since processes which increase oil content, yield, growth rate, biomass, vigor and/or abiotic stress tolerance of a plant can involve multiple genes acting additively or in synergy (see, for example, in Quesda et al., Plant Physiol. 130:951-063, 2002), the present invention also envisages expressing a plurality of exogenous polynucleotides in a single host plant to thereby achieve superior effect on oil content, yield, growth rate, biomass, vigor and/or abiotic stress tolerance.

Expressing a plurality of exogenous polynucleotides in a single host plant can be effected by co-introducing multiple nucleic acid constructs, each including a different exogenous polynucleotide, into a single plant cell. The transformed cell can than be regenerated into a mature plant using the methods described hereinabove.

Alternatively, expressing a plurality of exogenous polynucleotides in a single host plant can be effected by co-introducing into a single plant-cell a single nucleic-acid construct including a plurality of different exogenous polynucleotides. Such a construct can be designed with a single promoter sequence which can transcribe a polycistronic messenger RNA including all the different exogenous polynucleotide sequences. To enable co-translation of the different polypeptides encoded by the polycistronic messenger RNA, the polynucleotide sequences can be inter-linked via an internal ribosome entry site (IRES) sequence which facilitates translation of polynucleotide sequences positioned downstream of the IRES sequence. In this case, a transcribed polycistronic RNA molecule encoding the different polypeptides described above will be translated from both the capped 5′ end and the two internal IRES sequences of the polycistronic RNA molecule to thereby produce in the cell all different polypeptides. Alternatively, the construct can include several promoter sequences each linked to a different exogenous polynucleotide sequence.

The plant cell transformed with the construct including a plurality of different exogenous polynucleotides, can be regenerated into a mature plant, using the methods described hereinabove.

Alternatively, expressing a plurality of exogenous polynucleotides in a single host plant can be effected by introducing different nucleic acid constructs, including different exogenous polynucleotides, into a plurality of plants. The regenerated transformed plants can then be cross-bred and resultant progeny selected for superior abiotic stress tolerance, water use efficiency, fertilizer use efficiency, growth, biomass, yield and/or vigor traits, using conventional plant breeding techniques.

According to some embodiments of the invention, the method further comprising growing the plant expressing the exogenous polynucleotide under the abiotic stress.

Non-limiting examples of abiotic stress conditions include, salinity, drought, water deprivation, excess of water (e.g., flood, waterlogging), etiolation, low temperature, high temperature, heavy metal toxicity, anaerobiosis, nutrient deficiency, nutrient excess, atmospheric pollution and UV irradiation.

Thus, the invention encompasses plants exogenously expressing the polynucleotide(s), the nucleic acid constructs and/or polypeptide(s) of the invention. Once expressed within the plant cell or the entire plant, the level of the polypeptide encoded by the exogenous polynucleotide can be determined by methods well known in the art such as, activity assays, Western blots using antibodies capable of specifically binding the polypeptide, Enzyme-Linked Immuno Sorbent Assay (ELISA), radio-immuno-assays (RIA), immunohistochemistry, immunocytochemistry, immunofluorescence and the like.

Methods of determining the level in the plant of the RNA transcribed from the exogenous polynucleotide are well known in the art and include, for example, Northern blot analysis, reverse transcription polymerase chain reaction (RT-PCR) analysis (including quantitative, semi-quantitative or real-time RT-PCR) and RNA-in situ hybridization.

In addition, the endogenous homolog of the exogenous polynucleotide or polypeptide of the invention, or a fragment of the endogenous homolog (e.g. introns or untranslated regions) in the plant can be used as a marker for marker assisted selection (MAS), in which a marker is used for indirect selection of a genetic determinant or determinants of a trait of interest (e.g., biomass, growth rate, oil content, yield, abiotic stress tolerance). These genes (DNA or RNA sequence) may contain or be linked to polymorphic sites or genetic markers on the genome such as restriction fragment length polymorphism (RFLP), microsatellites and single nucleotide polymorphism (SNP), DNA fingerprinting (DFP), amplified fragment length polymorphism (AFLP), expression level polymorphism, polymorphism of the encoded polypeptide and any other polymorphism at the DNA or RNA sequence.

Examples of marker assisted selections include, but are not limited to, selection for a morphological trait (e.g., a gene that affects form, coloration, male sterility or resistance such as the presence or absence of awn, leaf sheath coloration, height, grain color, aroma of rice); selection for a biochemical trait (e.g., a gene that encodes a protein that can be extracted and observed; for example, isozymes and storage proteins); selection for a biological trait (e.g., pathogen races or insect biotypes based on host pathogen or host parasite interaction can be used as a marker since the genetic constitution of an organism can affect its susceptibility to pathogens or parasites).

The polynucleotides and polypeptides described hereinabove can be used in a wide range of economical plants, in a safe and cost effective manner.

Plant lines exogenously expressing the polynucleotide or the polypeptide of the invention are screened to identify those that show the greatest increase of the desired plant trait.

Following is a non-limiting description of assays which can be used to determine the effect of the transgene (the exogenous polynucleotide of some embodiments of the invention) or is encoded polypeptide on the trait-of-interest in a plant.

The main parameters of efficiency used to define plant Nitrogen (N) metabolism include nitrogen-uptake efficiency, nitrogen utilization efficiency, and nitrogen-use efficiency

The Nitrogen-uptake efficiency [the amount of N in above ground biomass (grams of nitrogen)/N applied (grams/hectare)] is the total amount of nitrogen incorporated by the plant and is a function of the “uptake” (the plant's transport capacity), the metabolic efficiency of the assimilation process and the rate of plant size development, since the mass of stalk and leaves created during growth are the actual Nitrogen-storage organs. The fraction of the assimilated Nitrogen found in a shoot that is ultimately transferred to the grain (yield) is controlled enzymatically, and thus can be affected by transgenic manipulation. This parameter is, in effect, equal to the Nitrogen Use efficiency (NUE). Better grain-to-shoot N-partitioning most likely will improve yield and protein content of the grain.

Similarly, the same calculations of use and utilization efficiencies can be made for other macronutrients such as Phosphorous (P) and Potassium (K), which have a direct correlation with yield and general plant tolerance.

Fertilizer Use Efficiency—

To analyze whether the transgenic plants are more responsive to fertilizers, plants are grown in agar plates or pots with a limited amount of fertilizer, as described, for example, in Examples 5-7 of the Example section which follows and in Yanagisawa et al (Proc Natl Acad Sci USA. 2004; 101:7833-8). The plants are analyzed for their overall size, time to flowering, yield, protein content of shoot and/or grain. The parameters checked are the overall size of the mature plant, its wet and dry weight, the weight of the seeds yielded, the average seed size and the number of seeds produced per plant. Other parameters that may be tested are: the chlorophyll content of leaves (as nitrogen plant status and the degree of leaf verdure is highly correlated), amino acid and the total protein content of the seeds or other plant parts such as leaves or shoots, oil content, etc. Similarly, instead of providing nitrogen at limiting amounts, phosphate or potassium can be added at increasing concentrations. Again, the same parameters measured are the same as listed above. In this way, nitrogen use efficiency (NUE), phosphate use efficiency (PUE) and potassium use efficiency (KUE) are assessed, checking the ability of the transgenic plants to thrive under nutrient restraining conditions.

Nitrogen Use Efficiency—

To analyze whether the transgenic Arabidopsis plants are more responsive to nitrogen, plant are grown in 0.75-1.5 mM (nitrogen deficient conditions) or 6-15 mM (optimal nitrogen concentration). Plants are allowed to grow for additional 20-40 days or until seed production. The plants are then analyzed for their overall size, time to flowering, yield, protein content of shoot and/or grain/seed production. The parameters checked can be the overall size of the plant, wet and dry weight, the weight of the seeds yielded, the average seed size and the number of seeds produced per plant. Other parameters that may be tested are: the chlorophyll content of leaves (as nitrogen plant status and the degree of leaf greenness is highly correlated), amino acid and the total protein content of the seeds or other plant parts such as leaves or shoots and oil content. Transformed plants not exhibiting substantial physiological and/or morphological effects, or exhibiting higher measured parameters levels than wild-type plants, are identified as nitrogen use efficient plants.

Nitrogen Determination—

The procedure for N (nitrogen) concentration determination in the structural parts of the plants involves the potassium persulfate digestion method to convert organic N to NO 3 − (Purcell and King 1996 Argon. J. 88:111-113, the modified Cd − mediated reduction of NO 3 − to NO 2 − (Vodovotz 1996 Biotechniques 20:390-394) and the measurement of nitrite by the Griess assay (Vodovotz 1996, supra). The absorbance values are measured at 550 nm against a standard curve of NaNO 2 . The procedure is described in details in Samonte et al. 2006 Agron. J. 98:168-176.

Germination Tests—

Germination tests compare the percentage of seeds from transgenic plants that could complete the germination process to the percentage of seeds from control plants that are treated in the same manner. Normal conditions are considered for example, incubations at 22° C. under 22-hour light 2-hour dark daily cycles. Evaluation of germination and seedling vigor is conducted between 4 and 14 days after planting. The basal media is 50% MS medium (Murashige and Skoog, 1962 Plant Physiology 15, 473-497).

Germination is checked also at unfavorable conditions such as cold (incubating at temperatures lower than 10° C. instead of 22° C.) or using seed inhibition solutions that contain high concentrations of an osmolyte such as sorbitol (at concentrations of 50 mM, 100 mM, 200 mM, 300 mM, 500 mM, and up to 1000 mM) or applying increasing concentrations of salt (of 50 mM, 100 mM, 200 mM, 300 mM, 500 mM NaCl).

The effect of the transgene on plant's vigor, growth rate, biomass, yield and/or oil content can be determined using known methods.

Plant Vigor—

The plant vigor can be calculated by the increase in growth parameters such as leaf area, fiber length, rosette diameter, plant fresh weight and the like per time.

Growth Rate—

The growth rate can be measured using digital analysis of growing plants. For example, images of plants growing in greenhouse on plot basis can be captured every 3 days and the rosette area can be calculated by digital analysis. Rosette area growth is calculated using the difference of rosette area between days of sampling divided by the difference in days between samples.

Evaluation of growth rate can be done by measuring plant biomass produced, rosette area, leaf size or root length per time (can be measured in cm 2 per day of leaf area).

Relative growth area can be calculated using Formula I.

Relative growth area rate=(ΔArea/Δ t )*(1/Area t 0 )  Formula I:

Δt is the current analyzed image day subtracted from the initial day (t−t0). Thus, the relative growth area rate is in units of 1/day and length growth rate is in units of 1/day.

Alternatively, the relative growth rate of the area can be calculated as the regression coefficient along time course.

Seed Yield—

Evaluation of the seed yield per plant can be done by measuring the amount (weight or size) or quantity (i.e., number) of dry seeds produced and harvested from 8-16 plants and divided by the number of plants.

For example, the total seeds from 8-16 plants can be collected, weighted using e.g., an analytical balance and the total weight can be divided by the number of plants. Seed yield per growing area can be calculated in the same manner while taking into account the growing area given to a single plant. Increase seed yield per growing area could be achieved by increasing seed yield per plant, and/or by increasing number of plants capable of growing in a given area.

In addition, seed yield can be determined via the weight of 1000 seeds. The weight of 1000 seeds can be determined as follows: seeds are scattered on a glass tray and a picture is taken. Each sample is weighted and then using the digital analysis, the number of seeds in each sample is calculated.

The 1000 seeds weight can be calculated using formula II:

1000 Seed Weight=number of seed in sample/sample weight×1000  Formula II:

The Harvest Index can be calculated using Formula III

Harvest Index=Average seed yield per plant/Average dry weight  Formula III:

Grain Protein Concentration—

Grain protein content (grams grain protein m −2 ) is estimated as the product of the mass of grain N (nitrogen) [grams grain Nitrogen m −2 ] multiplied by the N/protein conversion ratio of k-5.13 (Mosse 1990, supra). The grain protein concentration is estimated as the ratio of grain protein content per unit mass of the grain (grams grain protein kg −1 grain).

Fiber Length—

Fiber length can be measured using fibrograph. The fibrograph system was used to compute length in terms of “Upper Half Mean” length. The upper half mean (UHM) is the average length of longer half of the fiber distribution. The fibrograph measures length in span lengths at a given percentage point (Hypertext Transfer Protocol://World Wide Web (dot) cottonine (dot) com/ClassificationofCotton/?Pg=4#Length).

Oil Content—

The oil content of a plant can be determined by extraction of the oil from the seed or the vegetative portion of the plant. Briefly, lipids (oil) can be removed from the plant (e.g., seed) by grinding the plant tissue in the presence of specific solvents (e.g., hexane or petroleum ether) and extracting the oil in a continuous extractor. Indirect oil content analysis can be carried out using various known methods such as Nuclear Magnetic Resonance (NMR) Spectroscopy, which measures the resonance energy absorbed by hydrogen atoms in the liquid state of the sample [See for example, Conway T F. and Earle F R., 1963, Journal of the American Oil Chemists' Society; Springer Berlin/Heidelberg, ISSN: 0003-021X (Print) 1558-9331 (Online)]; the Near Infrared (NI) Spectroscopy, which utilizes the absorption of near infrared energy (1100-2500 nm) by the sample; and a method described in WO/2001/023884, which is based on extracting oil a solvent, evaporating the solvent in a gas stream which forms oil particles, and directing a light into the gas stream and oil particles which forms a detectable reflected light.

The effect of the transgene or its encoded polypeptide on abiotic stress tolerance can be determined using known methods.

Abiotic Stress Tolerance—

Transformed (i.e., expressing the transgene) and non-transformed (wild type) plants are exposed to an abiotic stress condition, such as water deprivation, suboptimal temperature (low temperature, high temperature), nutrient deficiency, nutrient excess, a salt stress condition, osmotic stress, heavy metal toxicity, anaerobiosis, atmospheric pollution and UV irradiation.

Salinity Tolerance Assay—

Transgenic plants with tolerance to high salt concentrations are expected to exhibit better germination, seedling vigor or growth in high salt. Salt stress can be effected in many ways such as, for example, by irrigating the plants with a hyperosmotic solution, by cultivating the plants hydroponically in a hyperosmotic growth solution (e.g., Hoagland solution), or by culturing the plants in a hyperosmotic growth medium [e.g., 50% Murashige-Skoog medium (MS medium)]. Since different plants vary considerably in their tolerance to salinity, the salt concentration in the irrigation water, growth solution, or growth medium can be adjusted according to the specific characteristics of the specific plant cultivar or variety, so as to inflict a mild or moderate effect on the physiology and/or morphology of the plants (for guidelines as to appropriate concentration see, Bernstein and Kafkafi, Root Growth Under Salinity Stress In: Plant Roots, The Hidden Half 3rd ed. Waisel Y, Eshel A and Kafkafi U. (editors) Marcel Dekker Inc., New York, 2002, and reference therein).

For example, a salinity tolerance test can be performed by irrigating plants at different developmental stages with increasing concentrations of sodium chloride (for example 50 mM, 100 mM, 200 mM, 400 mM NaCl) applied from the bottom and from above to ensure even dispersal of salt. Following exposure to the stress condition the plants are frequently monitored until substantial physiological and/or morphological effects appear in wild type plants. Thus, the external phenotypic appearance, degree of wilting and overall success to reach maturity and yield progeny are compared between control and transgenic plants. Quantitative parameters of tolerance measured include, but are not limited to, the average wet and dry weight, the weight of the seeds yielded, the average seed size and the number of seeds produced per plant. Transformed plants not exhibiting substantial physiological and/or morphological effects, or exhibiting higher biomass than wild-type plants, are identified as abiotic stress tolerant plants.

Osmotic Tolerance Test—

Osmotic stress assays (including sodium chloride and mannitol assays) are conducted to determine if an osmotic stress phenotype was sodium chloride-specific or if it was a general osmotic stress related phenotype. Plants which are tolerant to osmotic stress may have more tolerance to drought and/or freezing. For salt and osmotic stress germination experiments, the medium is supplemented for example with 50 mM, 100 mM, 200 mM NaCl or 100 mM, 200 mM NaCl, 400 mM mannitol, 500 mM sorbitol or 15 g (grams) PEG [Polyethylene Glycol 8000].

Drought Tolerance Assay/Osmoticum Assay—

Tolerance to drought is performed to identify the genes conferring better plant survival after acute water deprivation. To analyze whether the transgenic plants are more tolerant to drought, an osmotic stress produced by the non-ionic osmolyte sorbitol in the medium can be performed. Control and transgenic plants are germinated and grown in plant-agar plates for 4 days, after which they are transferred to plates containing 500 mM sorbitol. The treatment causes growth retardation, then both control and transgenic plants are compared, by measuring plant weight (wet and dry), yield, and by growth rates measured as time to flowering.

Conversely, soil-based drought screens are performed with plants overexpressing the polynucleotides detailed above. Seeds from control Arabidopsis plants, or other transgenic plants overexpressing the polypeptide of the invention are germinated and transferred to pots. Drought stress is obtained after irrigation is ceased accompanied by placing the pots on absorbent paper to enhance the soil-drying rate. Transgenic and control plants are compared to each other when the majority of the control plants develop severe wilting. Plants are re-watered after obtaining a significant fraction of the control plants displaying a severe wilting. Plants are ranked comparing to controls for each of two criteria: tolerance to the drought conditions and recovery (survival) following re-watering.

Cold Stress Tolerance—

To analyze cold stress, mature (25 day old) plants are transferred to 4° C. chambers for 1 or 2 weeks, with constitutive light. Later on plants are moved back to greenhouse. Two weeks later damages from chilling period, resulting in growth retardation and other phenotypes, are compared between both control and transgenic plants, by measuring plant weight (wet and dry), and by comparing growth rates measured as time to flowering, plant size, yield, and the like.

Heat Stress Tolerance—

Heat stress tolerance is achieved by exposing the plants to temperatures above 34° C. for a certain period. Plant tolerance is examined after transferring the plants back to 22° C. for recovery and evaluation after 5 days relative to internal controls (non-transgenic plants) or plants not exposed to neither cold or heat stress.

Water Use Efficiency—

can be determined as the biomass produced per unit transpiration. To analyze WUE, leaf relative water content can be measured in control and transgenic plants. Fresh weight (FW) is immediately recorded; then leaves are soaked for 8 hours in distilled water at room temperature in the dark, and the turgid weight (TW) is recorded. Total dry weight (DW) is recorded after drying the leaves at 60° C. to a constant weight. Relative water content (RWC) is calculated according to the following Formula IV:

RWC=[(FW−DW)/(TW−DW)]×100  Formula IV

Thus, the invention is of high agricultural value for promoting the yield of commercially desired crops (e.g., biomass of vegetative organ such as poplar wood, or reproductive organ such as number of seeds or seed biomass) under normal or growth-limiting conditions (e.g., nitrogen-deficient conditions, abiotic stress).

Any of the transgenic plants described hereinabove or parts thereof may be processed to produce a feed, meal, protein or oil preparation, such as for ruminant animals.

The transgenic plants described hereinabove, which exhibit an increased oil content can be used to produce plant oil (by extracting the oil from the plant).

The plant oil (including the seed oil and/or the vegetative portion oil) produced according to the method of the invention may be combined with a variety of other ingredients. The specific ingredients included in a product are determined according to the intended use. Exemplary products include animal feed, raw material for chemical modification, biodegradable plastic, blended food product, edible oil, biofuel, cooking oil, lubricant, biodiesel, snack food, cosmetics, and fermentation process raw material. Exemplary products to be incorporated to the plant oil include animal feeds, human food products such as extruded snack foods, breads, as a food binding agent, aquaculture feeds, fermentable mixtures, food supplements, sport drinks, nutritional food bars, multi-vitamin supplements, diet drinks, and cereal foods.

According to some embodiments of the invention, the oil comprises a seed oil and/or a vegetative portion oil.

According to some embodiments of the invention, the plant cell forms a part of a plant.

As used herein the term “about” refers to ±10%.

The terms “comprises”, “comprising”, “includes”, “including”, “having” and their conjugates mean “including but not limited to”.

The term “consisting of means “including and limited to”.

The term “consisting essentially of” means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise. For example, the term “a compound” or “at least one compound” may include a plurality of compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases “ranging/ranges between” a first indicate number and a second indicate number and “ranging/ranges from” a first indicate number “to” a second indicate number are used herein interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

As used herein the term “method” refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of the chemical, pharmacological, biological, biochemical and medical arts.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.

Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non limiting fashion.

Generally, the nomenclature used herein and the laboratory procedures utilized in the present invention include molecular, biochemical, microbiological and recombinant DNA techniques. Such techniques are thoroughly explained in the literature. See, for example, “Molecular Cloning: A laboratory Manual” Sambrook et al., (1989); “Current Protocols in Molecular Biology” Volumes I-III Ausubel, R. M., ed. (1994); Ausubel et al., “Current Protocols in Molecular Biology”, John Wiley and Sons, Baltimore, Md. (1989); Perbal, “A Practical Guide to Molecular Cloning”, John Wiley & Sons, New York (1988); Watson et al., “Recombinant DNA”, Scientific American Books, New York; Birren et al. (eds) “Genome Analysis: A Laboratory Manual Series”, Vols. 1-4, Cold Spring Harbor Laboratory Press, New York (1998); methodologies as set forth in U.S. Pat. Nos. 4,666,828; 4,683,202; 4,801,531; 5,192,659 and 5,272,057; “Cell Biology: A Laboratory Handbook”, Volumes I-III Cellis, J. E., ed. (1994); “Current Protocols in Immunology” Volumes I-III Coligan J. E., ed. (1994); Stites et al. (eds), “Basic and Clinical Immunology” (8th Edition), Appleton & Lange, Norwalk, Conn. (1994); Mishell and Shiigi (eds), “Selected Methods in Cellular Immunology”, W. H. Freeman and Co., New York (1980); available immunoassays are extensively described in the patent and scientific literature, see, for example, U.S. Pat. Nos. 3,791,932; 3,839,153; 3,850,752; 3,850,578; 3,853,987; 3,867,517; 3,879,262; 3,901,654; 3,935,074; 3,984,533; 3,996,345; 4,034,074; 4,098,876; 4,879,219; 5,011,771 and 5,281,521; “Oligonucleotide Synthesis” Gait, M. J., ed. (1984); “Nucleic Acid Hybridization” Hames, B. D., and Higgins S. J., eds. (1985); “Transcription and Translation” Hames, B. D., and Higgins S. J., Eds. (1984); “Animal Cell Culture” Freshney, R. I., ed. (1986); “Immobilized Cells and Enzymes” IRL Press, (1986); “A Practical Guide to Molecular Cloning” Perbal, B., (1984) and “Methods in Enzymology” Vol. 1-317, Academic Press; “PCR Protocols: A Guide To Methods And Applications”, Academic Press, San Diego, Calif. (1990); Marshak et al., “Strategies for Protein Purification and Characterization—A Laboratory Course Manual” CSHL Press (1996); all of which are incorporated by reference as if fully set forth herein. Other general references are provided throughout this document. The procedures therein are believed to be well known in the art and are provided for the convenience of the reader. All the information contained therein is incorporated herein by reference.