Patent Publication Number: US-2010115670-A1

Title: Nucleotide sequences and polypeptides encoded thereby useful for modifying plant characteristics in response to cold

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Nonprovisional application claims priority under 35 U.S.C. §119(e) of U.S. Provisional Application No. 60/859,467, filed Nov. 16, 2006, the entire contents of which are hereby incorporated by reference. 
    
    
     INCORPORATION-BY-REFERENCE OF SEQUENCE LISTING OR TABLE 
     The material in the accompanying sequence listing is hereby incorporated by reference into this application. The accompanying file, named 2007-10-29_Sequence Listing — 2750-1693W01.txt was created on Oct. 29, 2007 and is 447 KB. The file can be accessed using Microsoft Word on a computer that uses Windows OS. 
     TECHNICAL FIELD 
     This document relates to methods and materials involved in modulating cold tolerance in plants, including growth levels in plants growth under low or chilling temperature stress conditions (a.k.a. “cold stress”). For example, this document provides plants having increased growth rate, vegetative growth, seedling vigor and/or biomass under cold stress conditions as compared to wild-type plants grown under similar conditions, as well as materials and methods for making plants and plant products having increased growth levels under cold stress conditions. 
     BACKGROUND 
     Plants are constantly exposed to a variety of biotic (i.e. pathogen infection and insect herbivory) and abiotic (i.e. high or low temperature, drought, flood and salinity) stresses. To survive these challenges to their sessile life, plants have developed elaborate mechanisms to perceive external signals and to manifest adaptive responses with proper physiological and morphological changes (Bohnert et al. 1995). Plants exposed to cold or chilling conditions typically have low yields of biomass, seeds, fruit and other edible products. The term “chilling sensitivity” is used for the description of physiological and developmental damages in the plant caused by low, but above freezing, temperatures. Important agricultural crop plants such as corn, soybean, rice and cotton have tropical ancestors that make them chilling sensitive. In some countries or agricultural regions of the world chilling temperatures are a significant cause of crop losses and a primary factor limiting the geographical range and growing season of many crop species. Another example is that chilling conditions can cause significant concern in early spring planting of corn or canola. Poor germination and reduced growth of chilling sensitive crops in the spring results in less ground coverage, more erosion and increased occurrence of weeds leading to less nutrient supply for the crop. 
     Typically, chilling damage includes wilting, necrosis or ion leakage from cell membranes, especially calcium leakage, and decreased membrane fluidity, which consequently impacts membrane dependent processes such as: photosynthesis, protein synthesis, ATPase activity, uptake of nitrogen, etc. (see Levitt J (1980) Chilling injury and resistance. In Chilling, Freezing, and High Temperature Stresses: Responses of Plant to Environmental Stresses, Vol 1., T T Kozlowsky, ed, Academic Press, New York, pp 23-64; Graham and Patterson (1982)  Annu Rev Plant Physiol  33: 347-372; Guy (1990)  Annu Rev Plant Physiol Plant Mol Biol  41: 187-223; and Nishida and Murata (1996)  Annu Rev Plant Physiol Plant Mol Biol  47: 541-568.). In addition, cold temperatures are often associated with wet conditions. The combination of cold and wet can result in hypoxic stress on the roots, causing an even more severe reduction of growth rate but, more critically, can be lethal to the plants, especially sensitive plant species such as corn and cotton. 
     Yet it has been observed that environmental factors, such as low temperature, can serve as triggers to induce cold acclimation processes allowing plants responding thereto to survive and thrive in low temperature environments. It would, therefore, be of great interest and importance to be able to identify genes that regulate or confer improved cold acclimation characteristics to enable one to create transformed plants (such as crop plants) with improved cold tolerance characteristics such as faster germination and/or growth and/or improved nitrogen uptake under cold conditions to improve survival or performance under low or chilling temperatures. 
     In the fields of agriculture and forestry efforts are constantly being made to produce plants with an increased growth potential in order to feed the ever-increasing world population and to guarantee the supply of reproducible raw materials. This is done conventionally through plant breeding. The breeding process is, however, both time-consuming and labor-intensive. Furthermore, appropriate breeding programs must be performed for each relevant plant species. 
     Progress has been made in part by the genetic manipulation of plants; that is by introducing and expressing recombinant nucleic acid molecules in plants. Such approaches have the advantage of not usually being limited to one plant species, but instead being transferable among plant species. There is a need for generally applicable processes that improve forest or agricultural plant growth potential. Therefore, the present invention relates to a process for increasing the growth potential in plants under low temperature, chilling or cold conditions, characterized by expression of recombinant DNA molecules stably integrated into the plant genome. 
     SUMMARY 
     This document provides methods and materials related to plants having modulated levels of cold tolerance. For example, this document provides transgenic plants and plant cells having increased levels of cold tolerance, nucleic acids used to generate transgenic plants and plant cells having increased levels of cold tolerance, and methods for making plants and plant cells having increased levels of cold tolerance. Such plants and plant cells can be grown to produce, for example, plants having increased biomass content for fuel conversion or feed. Plants having increased biomass levels may be useful in converting such biomass to a liquid fuel or other chemicals, or may be useful as a thermochemical fuel. 
     Methods of producing a plant and/or plant tissue are provided herein. In one aspect, a method comprises growing a plant cell comprising an exogenous nucleic acid. The exogenous nucleic acid comprises a regulatory region operably linked to a nucleotide sequence encoding a polypeptide. The Hidden Markov Model (HMM) bit score of the amino acid sequence of the polypeptide is greater than about 40, using an HMM generated from the amino acid sequences depicted in one of  FIG. 1  or  2 . The plant and/or plant tissue has a difference in the level of cold tolerance as compared to the corresponding level of cold tolerance of a control plant that does not comprise the exogenous nucleic acid. 
     In certain embodiments, the amino acid sequence of the polypeptide is greater than about 40, using an HMM generated from the amino acid sequences depicted in one of  FIG. 1  or  2 , wherein the polypeptide comprises an auxin inducible domain having 80 percent or greater sequence identity to residues 1 to 106 of SEQ ID NO: 80, residues 1 to 102 of SEQ ID NO: 99, residues 1 to 92 of SEQ ID NO: 128, residues 5 to 104 of SEQ ID NO: 134, residues 20 to 128 of SEQ ID NO: 144, residues 1 to 91 of SEQ ID NO: 151, residues 7 to 105 of SEQ ID NO: 159, residues 86 to 155 of SEQ ID NO: 163, residues 37 to 146 of SEQ ID NO: 168, residues 25 to 86 of SEQ ID NO: 177, residues 51 to 119 of SEQ ID NO: 151, residues 70 to 124 of SEQ ID NO: 243, residues 10 to 102 of SEQ ID NO: 244, residues 4 to 114 of SEQ ID NO: 245, residues 32 to 92 of SEQ ID NO: 246, residues 58 to 119 of SEQ ID NO: 247, residues 48 to 113 of SEQ ID NO: 248, residues 48 to 108 of SEQ ID NO: 249, residues 22 to 111 of SEQ ID NO: 250, residues 5 to 105 of SEQ ID NO: 251, residues 7 to 101 of SEQ ID NO: 252, residues 22 to 115 of SEQ ID NO: 253, residues 6 to 108 of SEQ ID NO: 254, residues 28 to 96 of SEQ ID NO: 255, residues 7 to 104 of SEQ ID NO: 256, residues 1 to 89 of SEQ ID NO: 257, residues 11 to 105 of SEQ ID NO: 258, or residues 1 to 98 of SEQ ID NO: 259. 
     In another aspect, a method comprises growing a plant cell comprising an exogenous nucleic acid. The exogenous nucleic acid comprises a regulatory region operably linked to a nucleotide sequence encoding a polypeptide having 80 percent or greater sequence identity to an amino acid sequence set forth in SEQ ID NOs: 243, 180, 185, 178, 189, 186, 187, 276, 161, 182, 184, 218, 132, 183, 213, 195, 219, 236, 192, 268, 97, 179, 224, 274, 194, 157, 155, 242, 278, 272, 197, 232, 91, 48, 88, 85, 228, 81, 262, 169, 311, 226, 96, 93, 87, 309, 43, 115, 46, 83, 154, 105, 299, 104, 234, 94, 307, 18, 249, 102, 292, 95, 297, 293, 304, 62, 50, 92, 300, 114, 313, 16, 295, 14, 149, 305, 306, 117, 246, 8, 166, 22, 20, 217, 296, 147, 238, 270, 37, 103, 6, 279, 286, 66, 240, 244, 314, 255, 319, 153, 302, 148, 109, 130, 282, 264, 291, 41, 60, 107, 287, 116, 288, 82, 44, 301, 283, 78, 72, 266, 10, 211, 64, 247, 74, 77, 321, 229, 129, 325, 191, 128, 312, 231, 70, 248, 146, 68, 12, 1, 112, 4, 290, 27, 322, 56, 200, 280, 165, 31, 284, 221, 28, 159, 171, 250, 110, 257, 324, 245, 73, 58, 151, 320, 54, 52, 101, 99, 259, 142, 163, 135, 80, 168, 254, 318, 24, 256, 175, 316, 141, 76, 25, 39, 298, 140, 138, 177, 35, 230, 33, 253, 137, 323, 71, 251, 233, 30, 134, 2, 215, 75, 202, 252, 258, 260, 144, 173, 222, 126, 209, 206, 119, 204, 124, 123, 122, 207, or 121. A plant and/or plant tissue produced from the plant cell has a difference in the level of cold tolerance as compared to the corresponding level of cold tolerance of a control plant that does not comprise the exogenous nucleic acid. 
     In another aspect, the HMM bit score of the amino acid sequence of the polypeptide of the method of the invention is greater than about 40, said HMM based on the amino acid sequences depicted in one of  FIG. 1  or  2 . 
     In another aspect, a method comprises growing a plant cell comprising an exogenous nucleic acid. The exogenous nucleic acid comprises a regulatory region operably linked to a nucleotide sequence having 80 percent or greater sequence identity to at least a fragment of a nucleotide sequence set forth in SEQ ID NO: 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 26, 29, 32, 34, 36, 38, 40, 42, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 79, 84, 86, 89, 90, 100, 106, 108, 111, 113, 118, 120, 125, 127, 131, 133, 136, 139, 143, 145, 150, 152, 156, 158, 160, 162, 164, 167, 170, 172, 174, 176, 181, 188, 190, 193, 196, 198, 199, 201, 203, 205, 208, 210, 212, 214, 216, 220, 223, 225, 227, 235, 237, 239, 241, 261, 263, 265, 267, 269, 271, 273, 275, 277, 281, 285, 289, 294, 303, 308, 310, 315, 317, or 98. A plant and/or plant tissue produced from the plant cell has a difference in the level of cold tolerance as compared to the corresponding level of cold tolerance of a control plant that does not comprise the exogenous nucleic acid. 
     Methods of modulating the level of cold tolerance in a plant are provided herein. In one aspect, a method comprises introducing into a plant cell an exogenous nucleic acid, that comprises a regulatory region operably linked to a nucleotide sequence encoding a polypeptide. The HMM bit score of the amino acid sequence of the polypeptide is greater than about 40, using an HMM generated from the amino acid sequences depicted in one of  FIG. 1  or  2 . A plant and/or plant tissue produced from the plant cell has a difference in the level of cold tolerance as compared to the corresponding level of cold tolerance of a control plant that does not comprise the exogenous nucleic acid. 
     In another aspect, a method comprises introducing into a plant cell an exogenous nucleic acid that comprises a regulatory region operably linked to a nucleotide sequence encoding a polypeptide having 80 percent or greater sequence identity to an amino acid sequence set forth in SEQ ID NO: 243, 180, 185, 178, 189, 186, 187, 276, 161, 182, 184, 218, 132, 183, 213, 195, 219, 236, 192, 268, 97, 179, 224, 274, 194, 157, 155, 242, 278, 272, 197, 232, 91, 48, 88, 85, 228, 81, 262, 169, 311, 226, 96, 93, 87, 309, 43, 115, 46, 83, 154, 105, 299, 104, 234, 94, 307, 18, 249, 102, 292, 95, 297, 293, 304, 62, 50, 92, 300, 114, 313, 16, 295, 14, 149, 305, 306, 117, 246, 8, 166, 22, 20, 217, 296, 147, 238, 270, 37, 103, 6, 279, 286, 66, 240, 244, 314, 255, 319, 153, 302, 148, 109, 130, 282, 264, 291, 41, 60, 107, 287, 116, 288, 82, 44, 301, 283, 78, 72, 266, 10, 211, 64, 247, 74, 77, 321, 229, 129, 325, 191, 128, 312, 231, 70, 248, 146, 68, 12, 1, 112, 4, 290, 27, 322, 56, 200, 280, 165, 31, 284, 221, 28, 159, 171, 250, 110, 257, 324, 245, 73, 58, 151, 320, 54, 52, 101, 99, 259, 142, 163, 135, 80, 168, 254, 318, 24, 256, 175, 316, 141, 76, 25, 39, 298, 140, 138, 177, 35, 230, 33, 253, 137, 323, 71, 251, 233, 30, 134, 2, 215, 75, 202, 252, 258, 260, 144, 173, 222, 126, 209, 206, 119, 204, 124, 123, 122, 207, or 121. A plant and/or plant tissue produced from the plant cell has a difference in the level of cold tolerance as compared to the corresponding level of cold tolerance of a control plant that does not comprise the exogenous nucleic acid. 
     In another aspect, a method comprises introducing into a plant cell an exogenous nucleic acid, that comprises a regulatory region operably linked to a nucleotide sequence having 80 percent or greater sequence identity to a nucleotide sequence set forth in SEQ ID NO: 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 26, 29, 32, 34, 36, 38, 40, 42, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 79, 84, 86, 89, 90, 100, 106, 108, 111, 113, 118, 120, 125, 127, 131, 133, 136, 139, 143, 145, 150, 152, 156, 158, 160, 162, 164, 167, 170, 172, 174, 176, 181, 188, 190, 193, 196, 198, 199, 201, 203, 205, 208, 210, 212, 214, 216, 220, 223, 225, 227, 235, 237, 239, 241, 261, 263, 265, 267, 269, 271, 273, 275, 277, 281, 285, 289, 294, 303, 308, 310, 315, 317, or 98. A plant and/or plant tissue produced from the plant cell has a difference in the level of cold tolerance as compared to the corresponding level of cold tolerance of a control plant that does not comprise the exogenous nucleic acid. 
     Plant cells comprising an exogenous nucleic acid are provided herein. In one aspect, the exogenous nucleic acid comprises a regulatory region operably linked to a nucleotide sequence encoding a polypeptide. The HMM bit score of the amino acid sequence of the polypeptide is greater than about 40, using an HMM based on the amino acid sequences depicted in one of  FIG. 1  or  2 . The plant and/or plant tissue has a difference in the level of cold tolerance as compared to the corresponding level of cold tolerance of a control plant that does not comprise the exogenous nucleic acid. In another aspect, the exogenous nucleic acid comprises a regulatory region operably linked to a nucleotide sequence encoding a polypeptide having 80 percent or greater sequence identity to an amino acid sequence selected from the group consisting of SEQ ID NO: 243, 180, 185, 178, 189, 186, 187, 276, 161, 182, 184, 218, 132, 183, 213, 195, 219, 236, 192, 268, 97, 179, 224, 274, 194, 157, 155, 242, 278, 272, 197, 232, 91, 48, 88, 85, 228, 81, 262, 169, 311, 226, 96, 93, 87, 309, 43, 115, 46, 83, 154, 105, 299, 104, 234, 94, 307, 18, 249, 102, 292, 95, 297, 293, 304, 62, 50, 92, 300, 114, 313, 16, 295, 14, 149, 305, 306, 117, 246, 8, 166, 22, 20, 217, 296, 147, 238, 270, 37, 103, 6, 279, 286, 66, 240, 244, 314, 255, 319, 153, 302, 148, 109, 130, 282, 264, 291, 41, 60, 107, 287, 116, 288, 82, 44, 301, 283, 78, 72, 266, 10, 211, 64, 247, 74, 77, 321, 229, 129, 325, 191, 128, 312, 231, 70, 248, 146, 68, 12, 1, 112, 4, 290, 27, 322, 56, 200, 280, 165, 31, 284, 221, 28, 159, 171, 250, 110, 257, 324, 245, 73, 58, 151, 320, 54, 52, 101, 99, 259, 142, 163, 135, 80, 168, 254, 318, 24, 256, 175, 316, 141, 76, 25, 39, 298, 140, 138, 177, 35, 230, 33, 253, 137, 323, 71, 251, 233, 30, 134, 2, 215, 75, 202, 252, 258, 260, 144, 173, 222, 126, 209, 206, 119, 204, 124, 123, 122, 207, or 121. A plant and/or plant tissue produced from the plant cell has a difference in the level of cold tolerance as compared to the corresponding level of cold tolerance of a control plant that does not comprise the exogenous nucleic acid. In another aspect, the exogenous nucleic acid comprises a regulatory region operably linked to a nucleotide sequence having 80 percent or greater sequence identity to a nucleotide sequence selected from the group consisting of SEQ ID NO: 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 26, 29, 32, 34, 36, 38, 40, 42, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 79, 84, 86, 89, 90, 100, 106, 108, 111, 113, 118, 120, 125, 127, 131, 133, 136, 139, 143, 145, 150, 152, 156, 158, 160, 162, 164, 167, 170, 172, 174, 176, 181, 188, 190, 193, 196, 198, 199, 201, 203, 205, 208, 210, 212, 214, 216, 220, 223, 225, 227, 235, 237, 239, 241, 261, 263, 265, 267, 269, 271, 273, 275, 277, 281, 285, 289, 294, 303, 308, 310, 315, 317, or 98. A plant and/or plant tissue produced from the plant cell has a difference in the level of cold tolerance as compared to the corresponding level of cold tolerance of a control plant that does not comprise the exogenous nucleic acid. A transgenic plant comprising such a plant cell is also provided. Also provided is a seed and/or biomass product. The product comprises tissue from a cold tolerant transgenic plant. 
     Isolated nucleic acids are also provided. In one aspect, an isolated nucleic acid comprises a nucleotide sequence having 80% or greater sequence identity to the nucleotide sequence set forth in SEQ ID NOs: 196, 131, 120, 136, 11, 15, 69, 3, 106, 100, 86, 13, 203, 174, 5, 285, 7, 113, 55, 90, 303, 294, 145, 42, 49, 152, 45, 67, 57, 63, 40, 84, 181, 108, 289, 263, 267, 265, 235, 271, 273, 269, 261, 277, 239, 237, 275, 241, 188, 160, 125, 156, 193, 139, 26, 317, 208, 194, 214, 281, 220, 36, 188, 160, 125, 156, 315, 223, 193, 32, 38, 199, 201, 139, 227, 34, 9, 225, 205, 17, 65, 310, 61, 59, 210, 29, 47, 23, 19, 53, 242, 278, 30, or 27. In another aspect, an isolated nucleic acid comprises a nucleotide sequence encoding a polypeptide having 80% or greater sequence identity to the amino acid sequence set forth in SEQ ID NOs: 197, 132, 121, 137, 12, 16, 70, 4, 107, 101, 87, 14, 204, 175, 6, 286, 8, 114, 56, 1, 304, 295, 146, 43, 50, 153, 46, 68, 58, 64, 41, 85, 182, 109, 290, 264, 268, 266, 236, 272, 274, 270, 262, 278, 240, 238, 276, 242, 129, 91, 116, 81, 166, 138, 183, 189, 161, 126, 157, 194, 140, 149, 178, 142, 88, 93, 187, 155, 185, 148, 124, 117, 195, 27, 318, 209, 52, 215, 282, 221, 37, 189, 161, 126, 157, 316, 224, 194, 33, 39, 200, 202, 140, 228, 35, 10, 226, 206, 18, 66, 311, 62, 60, 211, 30, 48, 24, 20, 54, 243, 279, 31, or 28. 
     In another aspect, methods of identifying a genetic polymorphism associated with variation in the level of cold tolerance are provided. The methods include providing a population of plants, and determining whether one or more genetic polymorphisms in the population are genetically linked to the locus for a polypeptide selected from the group consisting of the polypeptides depicted in  FIG. 1  or  2  and functional homologs thereof. The correlation between variation in the level of cold tolerance in a tissue in plants of the population and the presence of the one or more genetic polymorphisms in plants of the population is measured, thereby permitting identification of whether or not the one or more genetic polymorphisms are associated with such variation. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and materials similar or equivalent to those described herein can be used to practice the invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a protein sequence alignment of small auxin-up RNAs (SAUR) protein family members, including ME12469 (SEQ ID NO: 80) and exemplary functional homologs thereof. In all the alignment figures shown herein, a dash in an aligned sequence represents a gap, i.e., a lack of an amino acid at that position. Identical amino acids or conserved amino acid substitutions among aligned sequences are identified by boxes.  FIG. 1  and the other alignment figures provided herein were generated using the program MUSCLE version 3.52. 
         FIG. 2  is a protein sequence alignment of ME09090 (SEQ ID NO: 119) and exemplary functional homologs thereof. 
     
    
    
     DETAILED DESCRIPTION 
     The invention features methods and materials related to modulating cold tolerance levels in plants. In some embodiments, the plants may also have modulated levels of growth under cold temperatures. The methods can include transforming a plant cell with a nucleic acid encoding a cold tolerance-modulating polypeptide, wherein expression of the polypeptide results in a modulated level of cold tolerance. Plant cells produced using such methods can be grown to produce plants having increased biomass content. Such plants, and the seeds of such plants, may be used to produce, for example, feeds and biofuels. 
     I. Definitions 
     “Amino acid” refers to one of the twenty biologically occurring amino acids and to synthetic amino acids, including D/L optical isomers. 
     “Cell type-preferential promoter” or “tissue-preferential promoter” refers to a promoter that drives expression preferentially in a target cell type or tissue, respectively, but may also lead to some transcription in other cell types or tissues as well. 
     “Cold.” Plant species vary in their capacity to tolerate low temperatures. Chilling-sensitive plant species, including many agronomically important species, can be injured by cold, above-freezing temperatures. At temperatures below the freezing-point of water most plant species will be damaged. Thus, “cold” can be defined as the temperature at which a given plant species will be adversely affected as evidenced by symptoms such as decreased photosynthesis and membrane damage (measured by electrolyte leakage). Since plant species vary in their capacity to tolerate cold, the precise environmental conditions that cause cold stress cannot be generalized. However, cold tolerant plants are characterized by their ability to retain their normal appearance, recover quickly from low temperature conditions, and/or exhibit normal or increased growth under low temperature conditions. Such cold tolerant plants produce higher biomass and yield than plants that are not cold tolerant. Differences in physical appearance, recovery and yield can be quantified and statistically analyzed using well known measurement and analysis methods. 
     Plant seeds vary considerably in their ability to germinate under cold conditions. Seeds of many plant species will not germinate at temperatures less than 10° C. Once seeds have imbibed water they become very susceptible to disease, water and chemical damage. Seeds that are tolerant to cold stress during germination can survive for relatively long periods under which the temperature is too low to germinate. Since plant species vary in their capacity to tolerate cold during germination, the precise environmental conditions that cause cold stress during germination can not be generalized. However, plants that tolerate cold during germination are characterized by their ability to remain viable or recover quickly from low temperature conditions. Such cold tolerant plants germinate, become established, grow more quickly and ultimately produce more biomass and yield than plants that are not cold tolerant. Differences in germination rate, appearance, recovery and yield can be quantified and statistically analyzed using well known measurement and analysis methods. 
     “Control plant” refers to a plant that does not contain the exogenous nucleic acid present in a transgenic plant of interest, but otherwise has the same or similar genetic background as such a transgenic plant. A suitable control plant can be a non-transgenic wild type plant, a non-transgenic segregant from a transformation experiment, or a transgenic plant that contains an exogenous nucleic acid other than the exogenous nucleic acid of interest. 
     “Domains” are groups of substantially contiguous amino acids in a polypeptide that can be used to characterize protein families and/or parts of proteins. Such domains have a “fingerprint” or “signature” that can comprise conserved primary sequence, secondary structure, and/or three-dimensional conformation. Generally, domains are correlated with specific in vitro and/or in vivo activities. A domain can have a length of from 10 amino acids to 400 amino acids, e.g., 10 to 50 amino acids, or 25 to 100 amino acids, or to 65 amino acids, or 35 to 55 amino acids, or 45 to 60 amino acids, or 200 to 300 amino acids, or 300 to 400 amino acids. 
     “Down-regulation” refers to regulation that decreases production of expression products (mRNA, polypeptide, or both) relative to basal or native states. 
     “Exogenous” with respect to a nucleic acid indicates that the nucleic acid is part of a recombinant nucleic acid construct, or is not in its natural environment. For example, an exogenous nucleic acid can be a sequence from one species introduced into another species, i.e., a heterologous nucleic acid. Typically, such an exogenous nucleic acid is introduced into the other species via a recombinant nucleic acid construct. An exogenous nucleic acid can also be a sequence that is native to an organism and that has been reintroduced into cells of that organism. An exogenous nucleic acid that includes a native sequence can often be distinguished from the naturally occurring sequence by the presence of non-natural sequences linked to the exogenous nucleic acid, e.g., non-native regulatory sequences flanking a native sequence in a recombinant nucleic acid construct. In addition, stably transformed exogenous nucleic acids typically are integrated at positions other than the position where the native sequence is found. It will be appreciated that an exogenous nucleic acid may have been introduced into a progenitor and not into the cell under consideration. For example, a transgenic plant containing an exogenous nucleic acid can be the progeny of a cross between a stably transformed plant and a non-transgenic plant. Such progeny are considered to contain the exogenous nucleic acid. 
     “Expression” refers to the process of converting genetic information of a polynucleotide into RNA through transcription, which is catalyzed by an enzyme, RNA polymerase, and into protein, through translation of mRNA on ribosomes. 
     “Heterologous polypeptide” as used herein refers to a polypeptide that is not a naturally occurring polypeptide in a plant cell, e.g., a transgenic  Panicum virgatum  plant transformed with and expressing the coding sequence for a nitrogen transporter polypeptide from a  Zea mays  plant. 
     “Isolated nucleic acid” as used herein includes a naturally-occurring nucleic acid, provided one or both of the sequences immediately flanking that nucleic acid in its naturally-occurring genome is removed or absent. Thus, an isolated nucleic acid includes, without limitation, a nucleic acid that exists as a purified molecule or a nucleic acid molecule that is incorporated into a vector or a virus. A nucleic acid existing among hundreds to millions of other nucleic acids within, for example, cDNA libraries, genomic libraries, or gel slices containing a genomic DNA restriction digest, is not to be considered an isolated nucleic acid. 
     “Modulation” of the level of cold tolerance refers to the change in the level of cold tolerance that is observed as a result of expression of, or transcription from, an exogenous nucleic acid in a plant cell. The change in level is measured relative to the corresponding level in control plants. 
     “Nucleic acid” and “polynucleotide” are used interchangeably herein, and refer to both RNA and DNA, including cDNA, genomic DNA, synthetic DNA, and DNA or RNA containing nucleic acid analogs. Polynucleotides can have any three-dimensional structure. A nucleic acid can be double-stranded or single-stranded (i.e., a sense strand or an antisense strand). Non-limiting examples of polynucleotides include genes, gene fragments, exons, introns, messenger RNA (mRNA), transfer RNA, ribosomal RNA, siRNA, micro-RNA, ribozymes, cDNA, recombinant polynucleotides, branched polynucleotides, nucleic acid probes and nucleic acid primers. A polynucleotide may contain unconventional or modified nucleotides. 
     “Operably linked” refers to the positioning of a regulatory region and a sequence to be transcribed in a nucleic acid so that the regulatory region is effective for regulating transcription or translation of the sequence. For example, to operably link a coding sequence and a regulatory region, the translation initiation site of the translational reading frame of the coding sequence is typically positioned between one and about fifty nucleotides downstream of the regulatory region. A regulatory region can, however, be positioned as much as about 5,000 nucleotides upstream of the translation initiation site, or about 2,000 nucleotides upstream of the transcription start site. 
     “Polypeptide” as used herein refers to a compound of two or more subunit amino acids, amino acid analogs, or other peptidomimetics, regardless of post-translational modification, e.g., phosphorylation or glycosylation. The subunits may be linked by peptide bonds or other bonds such as, for example, ester or ether bonds. Full-length polypeptides, truncated polypeptides, point mutants, insertion mutants, splice variants, chimeric proteins, and fragments thereof are encompassed by this definition. 
     “Progeny” includes descendants of a particular plant or plant line. Progeny of an instant plant include seeds formed on F 1 , F 2 , F 3 , F 4 , F 5 , F 6  and subsequent generation plants, or seeds formed on BC 1 , BC 2 , BC 3 , and subsequent generation plants, or seeds formed on F 1 BC 1 , F 1 BC 2 , F 1 BC 3 , and subsequent generation plants. The designation F 1  refers to the progeny of a cross between two parents that are genetically distinct. The designations F 2 , F 3 , F 4 , F 5  and F 6  refer to subsequent generations of self- or sib-pollinated progeny of an F 1  plant. 
     “Regulatory region” refers to a nucleic acid having nucleotide sequences that influence transcription or translation initiation and rate, and stability and/or mobility of a transcription or translation product. Regulatory regions include, without limitation, promoter sequences, enhancer sequences, response elements, protein recognition sites, inducible elements, protein binding sequences, 5′ and 3′ untranslated regions (UTRs), transcriptional start sites, termination sequences, polyadenylation sequences, introns, and combinations thereof. A regulatory region typically comprises at least a core (basal) promoter. A regulatory region also may include at least one control element, such as an enhancer sequence, an upstream element or an upstream activation region (UAR). For example, a suitable enhancer is a cis-regulatory element (−212 to −154) from the upstream region of the octopine synthase (ocs) gene. Fromm et al.,  The Plant Cell,  1:977-984 (1989). 
     “Up-regulation” refers to regulation that increases the level of an expression product (mRNA, polypeptide, or both) relative to basal or native states. 
     “Vector” refers to a replicon, such as a plasmid, phage, or cosmid, into which another DNA segment may be inserted so as to bring about the replication of the inserted segment. Generally, a vector is capable of replication when associated with the proper control elements. The term “vector” includes cloning and expression vectors, as well as viral vectors and integrating vectors. An “expression vector” is a vector that includes a regulatory region. 
     II. Polypeptides 
     Polypeptides described herein include cold tolerance-modulating polypeptides. Cold tolerance-modulating polypeptides can be effective to modulate cold tolerance levels when expressed in a plant or plant cell. Such polypeptides typically contain at least one domain indicative of cold tolerance-modulating polypeptides, as described in more detail herein. Cold tolerance-modulating polypeptides typically have an HMM bit score that is greater than 40, as described in more detail herein. In some embodiments, cold tolerance-modulating polypeptides have greater than 80% identity to SEQ ID NOs: 243, 180, 185, 178, 189, 186, 187, 276, 161, 182, 184, 218, 132, 183, 213, 195, 219, 236, 192, 268, 97, 179, 224, 274, 194, 157, 155, 242, 278, 272, 197, 232, 91, 48, 88, 85, 228, 81, 262, 169, 311, 226, 96, 93, 87, 309, 43, 115, 46, 83, 154, 105, 299, 104, 234, 94, 307, 18, 249, 102, 292, 95, 297, 293, 304, 62, 50, 92, 300, 114, 313, 16, 295, 14, 149, 305, 306, 117, 246, 8, 166, 22, 20, 217, 296, 147, 238, 270, 37, 103, 6, 279, 286, 66, 240, 244, 314, 255, 319, 153, 302, 148, 109, 130, 282, 264, 291, 41, 60, 107, 287, 116, 288, 82, 44, 301, 283, 78, 72, 266, 10, 211, 64, 247, 74, 77, 321, 229, 129, 325, 191, 128, 312, 231, 70, 248, 146, 68, 12, 1, 112, 4, 290, 27, 322, 56, 200, 280, 165, 31, 284, 221, 28, 159, 171, 250, 110, 257, 324, 245, 73, 58, 151, 320, 54, 52, 101, 99, 259, 142, 163, 135, 80, 168, 254, 318, 24, 256, 175, 316, 141, 76, 25, 39, 298, 140, 138, 177, 35, 230, 33, 253, 137, 323, 71, 251, 233, 30, 134, 2, 215, 75, 202, 252, 258, 260, 144, 173, 222, 126, 209, 206, 119, 204, 124, 123, 122, 207, and 121, as described in more detail herein. 
     A. Domains Indicative of Cold Tolerance-Modulating Polypeptides 
     A cold tolerance-modulating polypeptide can contain an auxin inducible domain, which is predicted to be characteristic of an auxin responsive protein. Such proteins are members of a family that consists of the protein products of a gene cluster that encodes a group of auxin-regulated RNAs (small auxin up RNAs, SAURs). For example, SEQ ID NO: 80 sets forth the amino acid sequence of an  Arabidopsis  clone, identified herein as Ceres Seedline ID no. ME12469 (SEQ ID NO:80), that is predicted to encode a polypeptide containing a auxin inducible domain. In certain embodiments, a cold tolerance-modulating polypeptide contains an auxin inducible domain having 80 percent or greater sequence identity to amino acid residues 1 to 106 of SEQ ID NO: 80, residues 1 to 102 of SEQ ID NO: 99, residues 1 to 92 of SEQ ID NO: 128, residues 5 to 104 of SEQ ID NO: 134, residues 20 to 128 of SEQ ID NO: 144, residues 1 to 91 of SEQ ID NO: 151, residues 7 to 105 of SEQ ID NO: 159, residues 86 to 155 of SEQ ID NO: 163, residues 37 to 146 of SEQ ID NO: 168, residues 25 to 86 of SEQ ID NO: 177, residues 51 to 119 of SEQ ID NO: 151, residues 70 to 124 of SEQ ID NO: 243, residues 10 to 102 of SEQ ID NO: 244, residues 4 to 114 of SEQ ID NO: 245, residues 32 to 92 of SEQ ID NO: 246, residues 58 to 119 of SEQ ID NO: 247, residues 48 to 113 of SEQ ID NO: 248, residues 48 to 108 of SEQ ID NO: 249, residues 22 to 111 of SEQ ID NO: 250, residues 5 to 105 of SEQ ID NO: 251, residues 7 to 101 of SEQ ID NO: 252, residues 22 to 115 of SEQ ID NO: 253, residues 6 to 108 of SEQ ID NO: 254, residues 28 to 96 of SEQ ID NO: 255, residues 7 to 104 of SEQ ID NO: 256, residues 1 to 89 of SEQ ID NO: 257, residues 11 to 105 of SEQ ID NO: 258, or residues 1 to 98 of SEQ ID NO: 259. 
     In certain embodiments, a cold tolerance-modulating polypeptide does not contain an auxin inducible and/or any recognizable Pfam domain. 
     B. Functional Homologs Identified by Reciprocal BLAST 
     In some embodiments, one or more functional homologs of a reference cold tolerance-modulating polypeptide defined by one or more of the Pfam descriptions indicated above are suitable for use as cold tolerance-modulating polypeptides. A functional homolog is a polypeptide that has sequence similarity to a reference polypeptide, and that carries out one or more of the biochemical or physiological function(s) of the reference polypeptide. A functional homolog and the reference polypeptide may be natural occurring polypeptides, and the sequence similarity may be due to convergent or divergent evolutionary events. As such, functional homologs are sometimes designated in the literature as homologs, or orthologs, or paralogs. Variants of a naturally occurring functional homolog, such as polypeptides encoded by mutants of a wild type coding sequence, may themselves be functional homologs. Functional homologs can also be created via site-directed mutagenesis of the coding sequence for a cold tolerance-modulating polypeptide, or by combining domains from the coding sequences for different naturally-occurring cold tolerance-modulating polypeptides (“domain swapping”). The term “functional homolog” is sometimes applied to the nucleic acid that encodes a functionally homologous polypeptide. 
     Functional homologs can be identified by analysis of nucleotide and polypeptide sequence alignments. For example, performing a query on a database of nucleotide or polypeptide sequences can identify homologs of cold tolerance-modulating polypeptides. Sequence analysis can involve BLAST, Reciprocal BLAST, or PSI-BLAST analysis of nonredundant databases using a cold tolerance-modulating polypeptide amino acid sequence as the reference sequence. Amino acid sequence is, in some instances, deduced from the nucleotide sequence. Those polypeptides in the database that have greater than 40% sequence identity are candidates for further evaluation for suitability as a cold tolerance-modulating polypeptide Amino acid sequence similarity allows for conservative amino acid substitutions, such as substitution of one hydrophobic residue for another or substitution of one polar residue for another. If desired, manual inspection of such candidates can be carried out in order to narrow the number of candidates to be further evaluated. Manual inspection can be performed by selecting those candidates that appear to have domains present in cold tolerance-modulating polypeptides, e.g., conserved functional domains. 
     Conserved regions can be identified by locating a region within the primary amino acid sequence of a cold tolerance-modulating polypeptide that is a repeated sequence, forms some secondary structure (e.g., helices and beta sheets), establishes positively or negatively charged domains, or represents a protein motif or domain See, e.g., the Pfam web site describing consensus sequences for a variety of protein motifs and domains on the World Wide Web at sanger.ac.uk/Software/Pfam/ and pfam.janelia.org/. A description of the information included at the Pfam database is described in Sonnhammer et al.,  Nucl. Acids Res.,  26:320-322 (1998); Sonnhammer et al.,  Proteins,  28:405-420 (1997); and Bateman et al.,  Nucl. Acids Res.,  27:260-262 (1999). Conserved regions also can be determined by aligning sequences of the same or related polypeptides from closely related species. Closely related species preferably are from the same family. In some embodiments, alignment of sequences from two different species is adequate. 
     Typically, polypeptides that exhibit at least about 40% amino acid sequence identity are useful to identify conserved regions. Conserved regions of related polypeptides exhibit at least 45% amino acid sequence identity (e.g., at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% amino acid sequence identity). In some embodiments, a conserved region exhibits at least 92%, 94%, 96%, 98%, or 99% amino acid sequence identity. 
     Amino acid sequences of functional homologs of the polypeptide set forth in SEQ ID NO:80 are provided in  FIG. 1  and in the Sequence Listing. Examples of such functional homologs include SEQ ID NOs: 71, 72, 73, 75, 80, 99, 101, 116, 128, 134, 144, 151, 159, 163, 168, 171, 173, 177, 191, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, and 279. In some cases, a functional homolog of SEQ ID NO:80 has an amino acid sequence with at least 45% sequence identity, e.g., 50%, 52%, 56%, 59%, 61%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, or 99% sequence identity, to the amino acid sequence set forth in SEQ ID NO:80. 
     Amino acid sequences of functional homologs of the polypeptide set forth in SEQ ID NO:119 are provided in  FIG. 2  and in the Sequence Listing. Examples of such functional homologs include SEQ ID NOs: 119, 121, 122, 123, 124, and 126. In some cases, a functional homolog of SEQ ID NO:119 has an amino acid sequence with at least 45% sequence identity, e.g., 50%, 52%, 56%, 59%, 61%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, or 99% sequence identity, to the amino acid sequence set forth in SEQ ID NO:119. 
     The identification of conserved regions in a cold tolerance-modulating polypeptide facilitates production of variants of cold tolerance-modulating polypeptides. Variants of cold tolerance-modulating polypeptides typically have 10 or fewer conservative amino acid substitutions within the primary amino acid sequence, e.g., 7 or fewer conservative amino acid substitutions, 5 or fewer conservative amino acid substitutions, or between 1 and 5 conservative substitutions. A useful variant polypeptide can be constructed based on one of the alignments set forth in  FIG. 1  or  FIG. 2 . Such a polypeptide includes the conserved regions, arranged in the order depicted in the Figure from amino-terminal end to carboxy-terminal end. Such a polypeptide may also include zero, one, or more than one amino acid in positions marked by dashes. When no amino acids are present at positions marked by dashes, the length of such a polypeptide is the sum of the amino acid residues in all conserved regions. When amino acids are present at all positions marked by dashes, such a polypeptide has a length that is the sum of the amino acid residues in all conserved regions and all dashes. 
     C. Functional Homologs Identified by HMMER 
     In some embodiments, useful cold tolerance-modulating polypeptides include those that fit a Hidden Markov Model based on the polypeptides set forth in any one of  FIGS. 1-2 . A Hidden Markov Model (HMM) is a statistical model of a consensus sequence for a group of functional homologs. See, Durbin et al.,  Biological Sequence Analysis: Probabilistic Models of Proteins and Nucleic Acids , Cambridge University Press, Cambridge, UK (1998). An HMM is generated by the program HMMER 2.3.2 with default program parameters, using the sequences of the group of functional homologs as input. The multiple sequence alignment is generated by ProbCons (Do et al., Genome Res., 15(2):330-40 (2005)) version 1.11 using a set of default parameters: -c, --consistency REPS of 2; -ir, --iterative-refinement REPS of 100; -pre, --pre-training REPS of 0. ProbCons is a public domain software program provided by Stanford University. 
     The default parameters for building an HMM (hmmbuild) are as follows: the default “architecture prior” (archpri) used by MAP architecture construction is 0.85, and the default cutoff threshold (idlevel) used to determine the effective sequence number is 0.62. HMMER 2.3.2 was released Oct. 3, 2003 under a GNU general public license, and is available from various sources on the World Wide Web such as hmmer janelia.org; hmmer.wustl.edu; and fr.com/hmmer232/. Hmmbuild outputs the model as a text file. 
     The HMM for a group of functional homologs can be used to determine the likelihood that a candidate cold tolerance-modulating polypeptide sequence is a better fit to that particular HMM than to a null HMM generated using a group of sequences that are not structurally or functionally related. The likelihood that a candidate polypeptide sequence is a better fit to an HMM than to a null HMM is indicated by the HMM bit score, a number generated when the candidate sequence is fitted to the HMM profile using the HMMER hmmsearch program. The following default parameters are used when running hmmsearch: the default E-value cutoff (E) is 10.0, the default bit score cutoff (T) is negative infinity, the default number of sequences in a database (Z) is the real number of sequences in the database, the default E-value cutoff for the per-domain ranked hit list (domE) is infinity, and the default bit score cutoff for the per-domain ranked hit list (domT) is negative infinity. A high HMM bit score indicates a greater likelihood that the candidate sequence carries out one or more of the biochemical or physiological function(s) of the polypeptides used to generate the HMM. A high HMM bit score is at least 20, and often is higher. Slight variations in the HMM bit score of a particular sequence can occur due to factors such as the order in which sequences are processed for alignment by multiple sequence alignment algorithms such as the ProbCons program. Nevertheless, such HMM bit score variation is minor. 
     The cold tolerance-modulating polypeptides discussed below fit the indicated HMM with an HMM bit score greater than 40 (e.g., greater than 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 1000, or 15000). In some embodiments, the HMM bit score of a cold tolerance-modulating polypeptide discussed below is about 50%, 60%, 70%, 80%, 90%, or 95% of the HMM bit score of a functional homolog provided in the Sequence Listing of this application. In some embodiments, a cold tolerance-modulating polypeptide discussed below fits the indicated HMM with an HMM bit score greater than 40, and has a domain indicative of a cold tolerance-modulating polypeptide. In some embodiments, a cold tolerance-modulating polypeptide discussed below fits the indicated HMM with an HMM bit score greater than 40, and has 70% or greater sequence identity (e.g., 75%, 80%, 85%, 90%, 95%, or 100% sequence identity) to an amino acid sequence shown in any one of  FIGS. 1-2 . 
     Examples of polypeptides that have HMM bit scores greater than 40 when fitted to an HMM generated from the amino acid sequences set forth in  FIG. 1  are identified in the Sequence Listing of this application. Such polypeptides include, but are not limited to, Ceres SEEDLINE ID no.ME25677, Ceres SEEDLINE ID no.ME25219, Ceres SEEDLINE ID no.ME25217, Ceres SEEDLINE ID no.ME02192, Ceres SEEDLINE ID no.ME25206, Ceres SEEDLINE ID no.ME25456, Ceres ANNOT ID 861093 ME14045, Ceres ME LINE ME00339, Ceres SEEDLINE ID no.ME25221, Ceres ME LINE ME14040, Ceres SEEDLINE ID no.ME02978, Ceres SEEDLINE ID no.ME07184, Ceres SEEDLINE ID no.ME25264, Ceres ME LINE ME12470, Ceres cDNA ID no. 23507179, Ceres SEEDLINE ID no.ME25243, Ceres ME LINE ME16427, Ceres SEEDLINE ID no. ME12469, Ceres ME LINE ME10853, Ceres SEEDLINE ID no.ME25205, Ceres SEEDLINE ID no.ME25209, Ceres ME LINE ME06899, Ceres SEEDLINE ID no.ME20371, Ceres SEEDLINE ID no.ME25211, Ceres ME LINE ME06788, Ceres SEEDLINE ID no.ME25266, Ceres SEEDLINE ID no.ME25265, Ceres ME LINE ME10877, Ceres ME LINE ME05746 (SEQ ID NOs: 80, 99, 128, 134, 144, 151, 159, 163, 168, 173, 177, 191, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259), and sequences in the Sequence Listing of this application with HMM bit scores correlated to  FIG. 1 . 
     Examples of polypeptides that have HMM bit scores greater than 70 when fitted to an HMM generated from the amino acid sequences set forth in  FIG. 2  are identified in the Sequence Listing of this application. Such polypeptides include, but are not limited to, Ceres CLONE ID no. 1775586, Ceres SEEDLINE ID no. ME09090, Ceres CLONE ID no. 918760, Public GI no. 82623371, Public GI no. 92883700, Ceres ANNOT ID no.1446889 (SEQ ID NOs: 119, 121, 122, 123, 124, 126), and sequences in the Sequence Listing of this application with HMM bit scores correlated to  FIG. 2 . 
     D. Percent Identity 
     In some embodiments, a cold tolerance-modulating polypeptide has an amino acid sequence with at least 45% sequence identity, e.g., 50%, 52%, 56%, 59%, 61%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, or 99% sequence identity, to one of the amino acid sequences set forth in SEQ ID NOs: 80, 99, 128, 134, 144, 151, 159, 163, 168, 173, 177, 191, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, and 119. Polypeptides having such a percent sequence identity often have a domain indicative of a cold tolerance-modulating polypeptide and/or have an HMM bit score that is greater than 40, as discussed above Amino acid sequences of cold tolerance-modulating polypeptides having at least 45% sequence identity to one of the amino acid sequences set forth in SEQ ID NOs: 80, 99, 128, 134, 144, 151, 159, 163, 168, 173, 177, 191, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, or 119 are provided in  FIGS. 1-2 . 
     “Percent sequence identity” refers to the degree of sequence identity between any given reference sequence, e.g., SEQ ID NO: 119, and a candidate cold tolerance-modulating sequence. A candidate sequence typically has a length that is from 80 percent to 200 percent of the length of the reference sequence, e.g., 82, 85, 87, 89, 90, 93, 95, 97, 99, 100, 105, 110, 115, 120, 130, 140, 150, 160, 170, 180, 190, or 200 percent of the length of the reference sequence. A percent identity for any candidate nucleic acid or polypeptide relative to a reference nucleic acid or polypeptide can be determined as follows. A reference sequence (e.g., a nucleic acid sequence or an amino acid sequence) is aligned to one or more candidate sequences using the computer program ClustalW (version 1.83, default parameters), which allows alignments of nucleic acid or polypeptide sequences to be carried out across their entire length (global alignment). Chema et al., Nucleic Acids Res., 31(13):3497-500 (2003). 
     ClustalW calculates the best match between a reference and one or more candidate sequences, and aligns them so that identities, similarities and differences can be determined. Gaps of one or more residues can be inserted into a reference sequence, a candidate sequence, or both, to maximize sequence alignments. For fast pairwise alignment of nucleic acid sequences, the following default parameters are used: word size: 2; window size: 4; scoring method: percentage; number of top diagonals: 4; and gap penalty: 5. For multiple alignment of nucleic acid sequences, the following parameters are used: gap opening penalty: 10.0; gap extension penalty: 5.0; and weight transitions: yes. For fast pairwise alignment of protein sequences, the following parameters are used: word size: 1; window size: 5; scoring method: percentage; number of top diagonals: 5; gap penalty: 3. For multiple alignment of protein sequences, the following parameters are used: weight matrix: blosum; gap opening penalty: 10.0; gap extension penalty: 0.05; hydrophilic gaps: on; hydrophilic residues: Gly, Pro, Ser, Asn, Asp, Gln, Glu, Arg, and Lys; residue-specific gap penalties: on. The ClustalW output is a sequence alignment that reflects the relationship between sequences. ClustalW can be run, for example, at the Baylor College of Medicine Search Launcher site (searchlauncher.bcm.tmc.edu/multi-align/multi-align.html) and at the European Bioinformatics Institute site on the World Wide Web (ebi.ac.uk/clustalw). 
     To determine percent identity of a candidate nucleic acid or amino acid sequence to a reference sequence, the sequences are aligned using ClustalW, the number of identical matches in the alignment is divided by the length of the reference sequence, and the result is multiplied by 100. It is noted that the percent identity value can be rounded to the nearest tenth. For example, 78.11, 78.12, 78.13, and 78.14 are rounded down to 78.1, while 78.15, 78.16, 78.17, 78.18, and 78.19 are rounded up to 78.2. 
     In some cases, a cold tolerance-modulating polypeptide has an amino acid sequence with at least 45% sequence identity, e.g., 50%, 52%, 56%, 59%, 61%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, or 99% sequence identity, to the amino acid sequence set forth in any one of SEQ ID NOs: 80, 99, 128, 134, 144, 151, 159, 163, 168, 173, 177, 191, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, or 259. Examples of amino acid sequences of polypeptides having greater than 45% sequence identity to the polypeptide set forth in any one of SEQ ID NOs: 80, 99, 128, 134, 144, 151, 159, 163, 168, 173, 177, 191, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, or 259 are provided in  FIG. 1  and/or the Sequence Listing of this application. Such polypeptides include, but are not limited to, Ceres CLONE ID no.1934672, Ceres CLONE ID no.1838450, Ceres ANNOT ID no.1450460, Public GI ID no.147856535, Ceres SEEDLINE ID no.ME13131, Ceres CLONE ID no.870882, Public GI ID no.147804681, Ceres SEEDLINE ID no.ME25267, and Ceres SEEDLINE ID no.ME05746 (SEQ ID NOs: 35, 33, 137, 323, 71, 30, 2, 75, and 260). 
     In some cases, a cold tolerance-modulating polypeptide has an amino acid sequence with at least 45% sequence identity, e.g., 50%, 52%, 56%, 59%, 61%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, or 99% sequence identity, to the amino acid sequence set forth in SEQ ID NO:119. Examples of amino acid sequences of polypeptides having greater than 45% sequence identity to the polypeptide set forth in SEQ ID NO: 119 are provided in  FIG. 2  and the Sequence Listing of this application. Such polypeptides include, but are not limited to, Ceres CLONE ID no. 1775586, Ceres CLONE ID no. 918760, Public GI no. 82623371, Public GI no. 92883700, and Ceres ANNOT ID no.1446889 (SEQ ID NOs: 121, 122, 123, 124, and 126). 
     E. Other Sequences 
     It should be appreciated that a cold tolerance-modulating polypeptide can include additional amino acids that are not involved in cold tolerance modulation, and thus such a polypeptide can be longer than would otherwise be the case. For example, a cold tolerance-modulating polypeptide can include a purification tag, a chloroplast transit peptide, a mitochondrial transit peptide, an amyloplast transit peptide, or a leader sequence added to the amino or carboxy terminus. In some embodiments, a cold tolerance-modulating polypeptide includes an amino acid sequence that functions as a reporter, e.g., a green fluorescent protein or yellow fluorescent protein. 
     III. Nucleic Acids 
     Nucleic acids described herein include nucleic acids that are effective to modulate cold tolerance levels when transcribed in a plant or plant cell. Such nucleic acids include, without limitation, those that encode a cold tolerance-modulating polypeptide and those that can be used to inhibit expression of a cold tolerance-modulating polypeptide via a nucleic acid based method. 
     A. Nucleic Acids Encoding Cold Tolerance-Modulating Polypeptides 
     Nucleic acids encoding cold tolerance-modulating polypeptides are described herein. Such nucleic acids include, but are not limited to, SEQ ID NOs: 190, 127, 172, 133, 176, 167, 143, 150, 158, 162, 79, 136, 11, 15, 69, 3, 106, 100, 86, 13, 174, 5, 285, 7, 89, 113, 55, 90, 303, 294, 145, 42, 49, 152, 45, 67, 57, 63, 164, 40, 111, 84, 181, 108, 289, 263, 267, 265, 271, 273, 269, 261, 277, 275, 26, 317, 51, 281, 36, 315, 32, 38, 34, 9, 17, 21, 65, 310, 61, 59, 308, 29, 47, 23, 19, 53, 170, 120, 203, 235, 239, 237, 241, 208, 214, 220, 223, 199, 201, 227, 225, 212, 216, 205, 210, and 118, as described in more detail below. 
     A cold tolerance-modulating nucleic acid can comprise the nucleotide sequence set forth in any one of SEQ ID NOs: 190, 127, 172, 133, 176, 167, 143, 150, 158, 162, or 79. Alternatively, a cold tolerance-modulating nucleic acid can be a variant of the nucleic acid having the nucleotide sequence set forth in any one of SEQ ID NOs: 190, 127, 172, 133, 176, 167, 143, 150, 158, 162, or 79. For example, a cold tolerance-modulating nucleic acid can have a nucleotide sequence with at least 80% sequence identity, e.g., 81%, 85%, 90%, 95%, 97%, 98%, or 99% sequence identity, to the nucleotide sequence set forth in any one of SEQ ID NOs: 190, 127, 172, 133, 176, 167, 143, 150, 158, 162, or 79. 
     A cold tolerance-modulating nucleic acid can comprise the nucleotide sequence set forth in SEQ ID NO:118. Alternatively, a cold tolerance-modulating nucleic acid can be a variant of the nucleic acid having the nucleotide sequence set forth in SEQ ID NO:118. For example, a cold tolerance-modulating nucleic acid can have a nucleotide sequence with at least 80% sequence identity, e.g., 81%, 85%, 90%, 95%, 97%, 98%, or 99% sequence identity, to the nucleotide sequence set forth in SEQ ID NO:118. 
     Isolated nucleic acid molecules can be produced by standard techniques. For example, polymerase chain reaction (PCR) techniques can be used to obtain an isolated nucleic acid containing a nucleotide sequence described herein. PCR can be used to amplify specific sequences from DNA as well as RNA, including sequences from total genomic DNA or total cellular RNA. Various PCR methods are described, for example, in PCR Primer: A Laboratory Manual, Dieffenbach and Dveksler, eds., Cold Spring Harbor Laboratory Press, 1995. Generally, sequence information from the ends of the region of interest or beyond is employed to design oligonucleotide primers that are identical or similar in sequence to opposite strands of the template to be amplified. Various PCR strategies also are available by which site-specific nucleotide sequence modifications can be introduced into a template nucleic acid. Isolated nucleic acids also can be chemically synthesized, either as a single nucleic acid molecule (e.g., using automated DNA synthesis in the 3′ to 5′ direction using phosphoramidite technology) or as a series of oligonucleotides. For example, one or more pairs of long oligonucleotides (e.g., &gt;100 nucleotides) can be synthesized that contain the desired sequence, with each pair containing a short segment of complementarity (e.g., about 15 nucleotides) such that a duplex is formed when the oligonucleotide pair is annealed. DNA polymerase is used to extend the oligonucleotides, resulting in a single, double-stranded nucleic acid molecule per oligonucleotide pair, which then can be ligated into a vector. Isolated nucleic acids of the invention also can be obtained by mutagenesis of, e.g., a naturally occurring DNA. 
     B. Use of Nucleic Acids to Modulate Expression of Polypeptides 
     i. Expression of a Cold Growth-Modulating Polypeptide 
     A nucleic acid encoding one of the cold growth-modulating polypeptides described herein can be used to express the polypeptide in a plant species of interest, typically by transforming a plant cell with a nucleic acid having the coding sequence for the polypeptide operably linked in sense orientation to one or more regulatory regions. It will be appreciated that because of the degeneracy of the genetic code, a number of nucleic acids can encode a particular cold growth-modulating polypeptide; i.e., for many amino acids, there is more than one nucleotide triplet that serves as the codon for the amino acid. Thus, codons in the coding sequence for a given cold growth-modulating polypeptide can be modified such that optimal expression in a particular plant species is obtained, using appropriate codon bias tables for that species. 
     In some cases, expression of a cold growth-modulating polypeptide inhibits one or more functions of an endogenous polypeptide. For example, a nucleic acid that encodes a dominant negative polypeptide can be used to inhibit protein function. A dominant negative polypeptide typically is mutated or truncated relative to an endogenous wild type polypeptide, and its presence in a cell inhibits one or more functions of the wild type polypeptide in that cell, i.e., the dominant negative polypeptide is genetically dominant and confers a loss of function. The mechanism by which a dominant negative polypeptide confers such a phenotype can vary but often involves a protein-protein interaction or a protein-DNA interaction. For example, a dominant negative polypeptide can be an enzyme that is truncated relative to a native wild type enzyme, such that the truncated polypeptide retains domains involved in binding a first protein but lacks domains involved in binding a second protein. The truncated polypeptide is thus unable to properly modulate the activity of the second protein. See, e.g., US 2007/0056058. As another example, a point mutation that results in a non-conservative amino acid substitution in a catalytic domain can result in a dominant negative polypeptide. See, e.g., US 2005/032221. As another example, a dominant negative polypeptide can be a transcription factor that is truncated relative to a native wild type transcription factor, such that the truncated polypeptide retains the DNA binding domain(s) but lacks the activation domain(s). Such a truncated polypeptide can inhibit the wild type transcription factor from binding DNA, thereby inhibiting transcription activation. 
     ii. Inhibition of Expression of a Cold Tolerance-Modulating Polypeptide 
     Polynucleotides and recombinant constructs described herein can be used to inhibit expression of a cold growth-modulating polypeptide in a plant species of interest. See, e.g., Matzke and Birchler,  Nature Reviews Genetics  6:24-35 (2005); Akashi et al.,  Nature Reviews Mol. Cell. Biology  6:413-422 (2005); Mittal,  Nature Reviews Genetics  5:355-365 (2004); Dorsett and Tuschl,  Nature Reviews Drug Discovery  3: 318-329 (2004); and  Nature Reviews RNA interference collection , October 2005 at nature.com/reviews/focus/mai. Typically, at least a fragment of a nucleic acids encoding cold growth-modulating polypeptides and/or its complement is expressed. A fragment is typically at least 20 nucleotides long, as needed for the methods noted below. A number of nucleic acid based methods, including antisense RNA, ribozyme directed RNA cleavage, post-transcriptional gene silencing (PTGS), e.g., RNA interference (RNAi), and transcriptional gene silencing (TGS) are known to inhibit gene expression in plants. Antisense technology is one well-known method. In this method, a nucleic acid segment from a gene to be repressed is cloned and operably linked to a regulatory region and a transcription termination sequence so that the antisense strand of RNA is transcribed. The recombinant construct is then transformed into plants, as described herein, and the antisense strand of RNA is produced. The nucleic acid segment need not be the entire sequence of the gene to be repressed, but typically will be substantially complementary to at least a portion of the sense strand of the gene to be repressed. Generally, higher homology can be used to compensate for the use of a shorter sequence. Typically, a sequence of at least 30 nucleotides is used, e.g., at least 40, 50, 80, 100, 200, 500 nucleotides or more. 
     In another method, a nucleic acid can be transcribed into a ribozyme, or catalytic RNA, that affects expression of an mRNA. See, U.S. Pat. No. 6,423,885. Ribozymes can be designed to specifically pair with virtually any target RNA and cleave the phosphodiester backbone at a specific location, thereby functionally inactivating the target RNA. Heterologous nucleic acids can encode ribozymes designed to cleave particular mRNA transcripts, thus preventing expression of a polypeptide. Hammerhead ribozymes are useful for destroying particular mRNAs, although various ribozymes that cleave mRNA at site-specific recognition sequences can be used. Hammerhead ribozymes cleave mRNAs at locations dictated by flanking regions that form complementary base pairs with the target mRNA. The sole requirement is that the target RNA contains a 5′-UG-3′ nucleotide sequence. The construction and production of hammerhead ribozymes is known in the art. See, for example, U.S. Pat. No. 5,254,678 and WO 02/46449 and references cited therein. Hammerhead ribozyme sequences can be embedded in a stable RNA such as a transfer RNA (tRNA) to increase cleavage efficiency in vivo. Perriman et al.,  Proc. Natl. Acad. Sci. USA,  92(13):6175-6179 (1995); de Feyter and Gaudron, Methods in Molecular Biology, Vol. 74, Chapter 43, “Expressing Ribozymes in Plants”, Edited by Turner, P. C., Humana Press Inc., Totowa, N.J. RNA endoribonucleases which have been described, such as the one that occurs naturally in  Tetrahymena thermophila , can be useful. See, for example, U.S. Pat. Nos. 4,987,071 and 6,423,885. 
     PTGS, e.g., RNAi, can also be used to inhibit the expression of a gene. For example, a construct can be prepared that includes a sequence that is transcribed into an RNA that can anneal to itself, e.g., a double stranded RNA having a stem-loop structure. In some embodiments, one strand of the stem portion of a double stranded RNA comprises a sequence that is similar or identical to the sense coding sequence of a cold growth-modulating polypeptide, and that is from about 10 nucleotides to about 2,500 nucleotides in length. The length of the sequence that is similar or identical to the sense coding sequence can be from 10 nucleotides to 500 nucleotides, from 15 nucleotides to 300 nucleotides, from 20 nucleotides to 100 nucleotides, or from 25 nucleotides to 100 nucleotides. The other strand of the stem portion of a double stranded RNA comprises a sequence that is similar or identical to the antisense strand of the coding sequence of the cold growth-modulating polypeptide, and can have a length that is shorter, the same as, or longer than the corresponding length of the sense sequence. In some cases, one strand of the stem portion of a double stranded RNA comprises a sequence that is similar or identical to the 3′ or 5′ untranslated region of an mRNA encoding a cold growth-modulating polypeptide, and the other strand of the stem portion of the double stranded RNA comprises a sequence that is similar or identical to the sequence that is complementary to the 3′ or 5′ untranslated region, respectively, of the mRNA encoding the cold growth-modulating polypeptide. In other embodiments, one strand of the stem portion of a double stranded RNA comprises a sequence that is similar or identical to the sequence of an intron in the pre-mRNA encoding a cold growth-modulating polypeptide, and the other strand of the stem portion comprises a sequence that is similar or identical to the sequence that is complementary to the sequence of the intron in the pre-mRNA. The loop portion of a double stranded RNA can be from 3 nucleotides to 5,000 nucleotides, e.g., from 3 nucleotides to 25 nucleotides, from 15 nucleotides to 1,000 nucleotides, from 20 nucleotides to 500 nucleotides, or from 25 nucleotides to 200 nucleotides. The loop portion of the RNA can include an intron. A double stranded RNA can have zero, one, two, three, four, five, six, seven, eight, nine, ten, or more stem-loop structures. A construct including a sequence that is operably linked to a regulatory region and a transcription termination sequence, and that is transcribed into an RNA that can form a double stranded RNA, is transformed into plants as described herein. Methods for using RNAi to inhibit the expression of a gene are known to those of skill in the art. See, e.g., U.S. Pat. Nos. 5,034,323; 6,326,527; 6,452,067; 6,573,099; 6,753,139; and 6,777,588. See also WO 97/01952; WO 98/53083; WO 99/32619; WO 98/36083; and U.S. Patent Publications 20030175965, 20030175783, 20040214330, and 20030180945. 
     Constructs containing regulatory regions operably linked to nucleic acid molecules in sense orientation can also be used to inhibit the expression of a gene. The transcription product can be similar or identical to the sense coding sequence of a cold growth-modulating polypeptide. The transcription product can also be unpolyadenylated, lack a 5′ cap structure, or contain an unspliceable intron. Methods of inhibiting gene expression using a full-length cDNA as well as a partial cDNA sequence are known in the art. See, e.g., U.S. Pat. No. 5,231,020. 
     In some embodiments, a construct containing a nucleic acid having at least one strand that is a template for both sense and antisense sequences that are complementary to each other is used to inhibit the expression of a gene. The sense and antisense sequences can be part of a larger nucleic acid molecule or can be part of separate nucleic acid molecules having sequences that are not complementary. The sense or antisense sequence can be a sequence that is identical or complementary to the sequence of an mRNA, the 3′ or 5′ untranslated region of an mRNA, or an intron in a pre-mRNA encoding a cold growth-modulating polypeptide. In some embodiments, the sense or antisense sequence is identical or complementary to a sequence of the regulatory region that drives transcription of the gene encoding a cold growth-modulating polypeptide. In each case, the sense sequence is the sequence that is complementary to the antisense sequence. 
     The sense and antisense sequences can be any length greater than about 12 nucleotides (e.g., 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, or more nucleotides). For example, an antisense sequence can be 21 or 22 nucleotides in length. Typically, the sense and antisense sequences range in length from about 15 nucleotides to about 30 nucleotides, e.g., from about 18 nucleotides to about 28 nucleotides, or from about 21 nucleotides to about 25 nucleotides. 
     In some embodiments, an antisense sequence is a sequence complementary to an mRNA sequence encoding a cold growth-modulating polypeptide described herein. The sense sequence complementary to the antisense sequence can be a sequence present within the mRNA of the cold growth-modulating polypeptide. Typically, sense and antisense sequences are designed to correspond to a 15-30 nucleotide sequence of a target mRNA such that the level of that target mRNA is reduced. 
     In some embodiments, a construct containing a nucleic acid having at least one strand that is a template for more than one sense sequence (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10 or more sense sequences) can be used to inhibit the expression of a gene. Likewise, a construct containing a nucleic acid having at least one strand that is a template for more than one antisense sequence (e.g., 2, 3, 4, 5, 6, 7, 8, 9, 10 or more antisense sequences) can be used to inhibit the expression of a gene. For example, a construct can contain a nucleic acid having at least one strand that is a template for two sense sequences and two antisense sequences. The multiple sense sequences can be identical or different, and the multiple antisense sequences can be identical or different. For example, a construct can have a nucleic acid having one strand that is a template for two identical sense sequences and two identical antisense sequences that are complementary to the two identical sense sequences. Alternatively, an isolated nucleic acid can have one strand that is a template for (1) two identical sense sequences 20 nucleotides in length, (2) one antisense sequence that is complementary to the two identical sense sequences 20 nucleotides in length, (3) a sense sequence 30 nucleotides in length, and (4) three identical antisense sequences that are complementary to the sense sequence 30 nucleotides in length. The constructs provided herein can be designed to have any arrangement of sense and antisense sequences. For example, two identical sense sequences can be followed by two identical antisense sequences or can be positioned between two identical antisense sequences. 
     A nucleic acid having at least one strand that is a template for one or more sense and/or antisense sequences can be operably linked to a regulatory region to drive transcription of an RNA molecule containing the sense and/or antisense sequence(s). In addition, such a nucleic acid can be operably linked to a transcription terminator sequence, such as the terminator of the nopaline synthase (nos) gene. In some cases, two regulatory regions can direct transcription of two transcripts: one from the top strand, and one from the bottom strand. See, for example, Yan et al.,  Plant Physiol.,  141:1508-1518 (2006). The two regulatory regions can be the same or different. The two transcripts can form double-stranded RNA molecules that induce degradation of the target RNA. In some cases, a nucleic acid can be positioned within a T-DNA or plant-derived transfer DNA (P-DNA) such that the left and right T-DNA border sequences, or the left and right border-like sequences of the P-DNA, flank or are on either side of the nucleic acid. See, US 2006/0265788. The nucleic acid sequence between the two regulatory regions can be from about 15 to about 300 nucleotides in length. In some embodiments, the nucleic acid sequence between the two regulatory regions is from about 15 to about 200 nucleotides in length, from about 15 to about 100 nucleotides in length, from about 15 to about 50 nucleotides in length, from about 18 to about 50 nucleotides in length, from about 18 to about 40 nucleotides in length, from about 18 to about 30 nucleotides in length, or from about 18 to about 25 nucleotides in length. 
     In some nucleic-acid based methods for inhibition of gene expression in plants, a suitable nucleic acid can be a nucleic acid analog. Nucleic acid analogs can be modified at the base moiety, sugar moiety, or phosphate backbone to improve, for example, stability, hybridization, or solubility of the nucleic acid. Modifications at the base moiety include deoxyuridine for deoxythymidine, and 5-methyl-2′-deoxycytidine and 5-bromo-2′-deoxycytidine for deoxycytidine. Modifications of the sugar moiety include modification of the 2′ hydroxyl of the ribose sugar to form 2′-O-methyl or 2′-O-allyl sugars. The deoxyribose phosphate backbone can be modified to produce morpholino nucleic acids, in which each base moiety is linked to a six-membered morpholino ring, or peptide nucleic acids, in which the deoxyphosphate backbone is replaced by a pseudopeptide backbone and the four bases are retained. See, for example, Summerton and Weller, 1997,  Antisense Nucleic Acid Drug Dev.,  7:187-195; Hyrup et al.,  Bioorgan. Med. Chem.,  4:5-23 (1996). In addition, the deoxyphosphate backbone can be replaced with, for example, a phosphorothioate or phosphorodithioate backbone, a phosphoroamidite, or an alkyl phosphotriester backbone. 
     C. Constructs/Vectors 
     Recombinant constructs provided herein can be used to transform plants or plant cells in order to modulate cold growth levels. A recombinant nucleic acid construct can comprise a nucleic acid encoding a cold growth-modulating polypeptide as described herein, operably linked to a regulatory region suitable for expressing the cold growth-modulating polypeptide in the plant or cell. Thus, a nucleic acid can comprise a coding sequence that encodes any of the cold growth-modulating polypeptides as set forth in SEQ ID NOs: 243, 180, 185, 178, 189, 186, 187, 276, 161, 182, 184, 218, 132, 183, 213, 195, 219, 236, 192, 268, 97, 179, 224, 274, 194, 157, 155, 242, 278, 272, 197, 232, 91, 48, 88, 85, 228, 81, 262, 169, 311, 226, 96, 93, 87, 309, 43, 115, 46, 83, 154, 105, 299, 104, 234, 94, 307, 18, 249, 102, 292, 95, 297, 293, 304, 62, 50, 92, 300, 114, 313, 16, 295, 14, 149, 305, 306, 117, 246, 8, 166, 22, 20, 217, 296, 147, 238, 270, 37, 103, 6, 279, 286, 66, 240, 244, 314, 255, 319, 153, 302, 148, 109, 130, 282, 264, 291, 41, 60, 107, 287, 116, 288, 82, 44, 301, 283, 78, 72, 266, 10, 211, 64, 247, 74, 77, 321, 229, 129, 325, 191, 128, 312, 231, 70, 248, 146, 68, 12, 1, 112, 4, 290, 27, 322, 56, 200, 280, 165, 31, 284, 221, 28, 159, 171, 250, 110, 257, 324, 245, 73, 58, 151, 320, 54, 52, 101, 99, 259, 142, 163, 135, 80, 168, 254, 318, 24, 256, 175, 316, 141, 76, 25, 39, 298, 140, 138, 177, 35, 230, 33, 253, 137, 323, 71, 251, 233, 30, 134, 2, 215, 75, 202, 252, 258, 260, 144, 173, 222, 126, 209, 206, 119, 204, 124, 123, 122, 207, or 121. Examples of nucleic acids encoding cold growth-modulating polypeptides are set forth in SEQ ID NOs: 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 26, 29, 32, 34, 36, 38, 40, 42, 45, 47, 49, 51, 53, 55, 57, 59, 61, 63, 65, 67, 69, 79, 84, 86, 89, 90, 100, 106, 108, 111, 113, 118, 120, 125, 127, 131, 133, 136, 139, 143, 145, 150, 152, 156, 158, 160, 162, 164, 167, 170, 172, 174, 176, 181, 188, 190, 193, 196, 198, 199, 201, 203, 205, 208, 210, 212, 214, 216, 220, 223, 225, 227, 235, 237, 239, 241, 261, 263, 265, 267, 269, 271, 273, 275, 277, 281, 285, 289, 294, 303, 308, 310, 315, 317, or 98. The cold growth-modulating polypeptide encoded by a recombinant nucleic acid can be a native cold growth-modulating polypeptide, or can be heterologous to the cell. In some cases, the recombinant construct contains a nucleic acid that inhibits expression of a cold growth-modulating polypeptide, operably linked to a regulatory region. Examples of suitable regulatory regions are described in the section entitled “Regulatory Regions.” 
     Vectors containing recombinant nucleic acid constructs such as those described herein also are provided. Suitable vector backbones include, for example, those routinely used in the art such as plasmids, viruses, artificial chromosomes, BACs, YACs, or PACs. Suitable expression vectors include, without limitation, plasmids and viral vectors derived from, for example, bacteriophage, baculoviruses, and retroviruses. Numerous vectors and expression systems are commercially available from such corporations as Novagen (Madison, Wis.), Clontech (Palo Alto, Calif.), Stratagene (La Jolla, Calif.), and Invitrogen/Life Technologies (Carlsbad, Calif.). 
     The vectors provided herein also can include, for example, origins of replication, scaffold attachment regions (SARs), and/or markers. A marker gene can confer a selectable phenotype on a plant cell. For example, a marker can confer biocide resistance, such as resistance to an antibiotic (e.g., kanamycin, G418, bleomycin, or hygromycin), or an herbicide (e.g., glyphosate, chlorsulfuron or phosphinothricin). In addition, an expression vector can include a tag sequence designed to facilitate manipulation or detection (e.g., purification or localization) of the expressed polypeptide. Tag sequences, such as luciferase, β-glucuronidase (GUS), green fluorescent protein (GFP), glutathione S-transferase (GST), polyhistidine, c-myc, hemagglutinin, or Flag™ tag (Kodak, New Haven, Conn.) sequences typically are expressed as a fusion with the encoded polypeptide. Such tags can be inserted anywhere within the polypeptide, including at either the carboxyl or amino terminus. 
     D. Regulatory Regions 
     The choice of regulatory regions to be included in a recombinant construct depends upon several factors, including, but not limited to, efficiency, selectability, inducibility, desired expression level, and cell- or tissue-preferential expression. It is a routine matter for one of skill in the art to modulate the expression of a coding sequence by appropriately selecting and positioning regulatory regions relative to the coding sequence. Transcription of a nucleic acid can be modulated in a similar manner. 
     Some suitable regulatory regions initiate transcription only, or predominantly, in certain cell types. Methods for identifying and characterizing regulatory regions in plant genomic DNA are known, including, for example, those described in the following references: Jordano et al.,  Plant Cell,  1:855-866 (1989); Bustos et al.,  Plant Cell,  1:839-854 (1989); Green et al.,  EMBO J.,  7:4035-4044 (1988); Meier et al.,  Plant Cell,  3:309-316 (1991); and Zhang et al.,  Plant Physiology,  110:1069-1079 (1996). 
     Examples of various classes of regulatory regions are described below. Some of the regulatory regions indicated below as well as additional regulatory regions are described in more detail in U.S. Patent Application Ser. Nos. 60/505,689; 60/518,075; 60/544,771; 60/558,869; 60/583,691; 60/619,181; 60/637,140; 60/757,544; 60/776,307; 10/957,569; 11/058,689; 11/172,703; 11/208,308; 11/274,890; 60/583,609; 60/612,891; 11/097,589; 11/233,726; 11/408,791; 11/414,142; 10/950,321; 11/360,017; PCT/US05/011105; PCT/US05/23639; PCT/US05/034308; PCT/US05/034343; and PCT/US06/038236; PCT/US06/040572; and PCT/US07/62762. 
     For example, the sequences of regulatory regions p326, YP0144, YP0190, p13879, YP0050, p32449, 21876, YP0158, YP0214, YP0380, PT0848, PT0633, YP0128, YP0275, PT0660, PT0683, PT0758, PT0613, PT0672, PT0688, PT0837, YP0092, PT0676, PT0708, YP0396, YP0007, YP0111, YP0103, YP0028, YP0121, YP0008, YP0039, YP0115, YP0119, YP0120, YP0374, YP0101, YP0102, YP0110, YP0117, YP0137, YP0285, YP0212, YP0097, YP0107, YP0088, YP0143, YP0156, PT0650, PT0695, PT0723, PT0838, PT0879, PT0740, PT0535, PT0668, PT0886, PT0585, YP0381, YP0337, PT0710, YP0356, YP0385, YP0384, YP0286, YP0377, PD1367, PT0863, PT0829, PT0665, PT0678, YP0086, YP0188, YP0263, PT0743 and YP0096 are set forth in the sequence listing of PCT/US06/040572; the sequence of regulatory region PT0625 is set forth in the sequence listing of PCT/US05/034343; the sequences of regulatory regions PT0623, YP0388, YP0087, YP0093, YP0108, YP0022 and YP0080 are set forth in the sequence listing of U.S. patent application Ser. No. 11/172,703; the sequence of regulatory region PR0924 is set forth in the sequence listing of PCT/US07/62762; and the sequences of regulatory regions p530c10, pOsFIE2-2, pOsMEA, pOsYp102, and pOsYp285 are set forth in the sequence listing of PCT/US06/038236. 
     It will be appreciated that a regulatory region may meet criteria for one classification based on its activity in one plant species, and yet meet criteria for a different classification based on its activity in another plant species. 
     i. Broadly Expressing Promoters 
     A promoter can be said to be “broadly expressing” when it promotes transcription in many, but not necessarily all, plant tissues. For example, a broadly expressing promoter can promote transcription of an operably linked sequence in one or more of the shoot, shoot tip (apex), and leaves, but weakly or not at all in tissues such as roots or stems. As another example, a broadly expressing promoter can promote transcription of an operably linked sequence in one or more of the stem, shoot, shoot tip (apex), and leaves, but can promote transcription weakly or not at all in tissues such as reproductive tissues of flowers and developing seeds. Non-limiting examples of broadly expressing promoters that can be included in the nucleic acid constructs provided herein include the p326, YP0144, YP0190, p13879, YP0050, p32449, 21876, YP0158, YP0214, YP0380, PT0848, and PT0633 promoters. Additional examples include the cauliflower mosaic virus (CaMV) 35S promoter, the mannopine synthase (MAS) promoter, the 1′ or 2′ promoters derived from T-DNA of  Agrobacterium tumefaciens , the figwort mosaic virus 34S promoter, actin promoters such as the rice actin promoter, and ubiquitin promoters such as the maize ubiquitin-1 promoter. In some cases, the CaMV 35S promoter is excluded from the category of broadly expressing promoters. 
     ii. Root Promoters 
     Root-active promoters confer transcription in root tissue, e.g., root endodermis, root epidermis, or root vascular tissues. In some embodiments, root-active promoters are root-preferential promoters, i.e., confer transcription only or predominantly in root tissue. Root-preferential promoters include the YP0128, YP0275, PT0625, PT0660, PT0683, and PT0758 promoters. Other root-preferential promoters include the PT0613, PT0672, PT0688, and PT0837 promoters, which drive transcription primarily in root tissue and to a lesser extent in ovules and/or seeds. Other examples of root-preferential promoters include the root-specific subdomains of the CaMV 35S promoter (Lam et al.,  Proc. Natl. Acad. Sci. USA,  86:7890-7894 (1989)), root cell specific promoters reported by Conkling et al.,  Plant Physiol.,  93:1203-1211 (1990), and the tobacco RD2 promoter. 
     iii. Maturing Endosperm Promoters 
     In some embodiments, promoters that drive transcription in maturing endosperm can be useful. Transcription from a maturing endosperm promoter typically begins after fertilization and occurs primarily in endosperm tissue during seed development and is typically highest during the cellularization phase. Most suitable are promoters that are active predominantly in maturing endosperm, although promoters that are also active in other tissues can sometimes be used. Non-limiting examples of maturing endosperm promoters that can be included in the nucleic acid constructs provided herein include the napin promoter, the Arcelin-5 promoter, the phaseolin promoter (Bustos et al.,  Plant Cell,  1(9):839-853 (1989)), the soybean trypsin inhibitor promoter (Riggs et al.,  Plant Cell,  1(6):609-621 (1989)), the ACP promoter (Baerson et al.,  Plant Mol. Biol.,  22(2):255-267 (1993)), the stearoyl-ACP desaturase promoter (Slocombe et al.,  Plant Physiol.,  104(4):167-176 (1994)), the soybean α′ subunit of β-conglycinin promoter (Chen et al.,  Proc. Natl. Acad. Sci. USA,  83:8560-8564 (1986)), the oleosin promoter (Hong et al.,  Plant Mol. Biol.,  34(3):549-555 (1997)), and zein promoters, such as the 15 kD zein promoter, the 16 kD zein promoter, 19 kD zein promoter, 22 kD zein promoter and 27 kD zein promoter. Also suitable are the Osgt-1 promoter from the rice glutelin-1 gene (Zheng et al.,  Mol. Cell. Biol.,  13:5829-5842 (1993)), the beta-amylase promoter, and the barley hordein promoter. Other maturing endosperm promoters include the YP0092, PT0676, and PT0708 promoters. 
     iv. Ovary Tissue Promoters 
     Promoters that are active in ovary tissues such as the ovule wall and mesocarp can also be useful, e.g., a polygalacturonidase promoter, the banana TRX promoter, the melon actin promoter, YP0396, and PT0623. Examples of promoters that are active primarily in ovules include YP0007, YP0111, YP0092, YP0103, YP0028, YP0121, YP0008, YP0039, YP0115, YP0119, YP0120, and YP0374. 
     v. Embryo Sac/Early Endosperm Promoters 
     To achieve expression in embryo sac/early endosperm, regulatory regions can be used that are active in polar nuclei and/or the central cell, or in precursors to polar nuclei, but not in egg cells or precursors to egg cells. Most suitable are promoters that drive expression only or predominantly in polar nuclei or precursors thereto and/or the central cell. A pattern of transcription that extends from polar nuclei into early endosperm development can also be found with embryo sac/early endosperm-preferential promoters, although transcription typically decreases significantly in later endosperm development during and after the cellularization phase. Expression in the zygote or developing embryo typically is not present with embryo sac/early endosperm promoters. 
     Promoters that may be suitable include those derived from the following genes:  Arabidopsis  viviparous-1 (see, GenBank No. U93215);  Arabidopsis  atmycl (see, Urao (1996)  Plant Mol. Biol.,  32:571-57; Conceicao (1994)  Plant,  5:493-505);  Arabidopsis  FIE (GenBank No. AF129516);  Arabidopsis  MEA;  Arabidopsis  FIS2 (GenBank No. AF096096); and FIE 1.1 (U.S. Pat. No. 6,906,244). Other promoters that may be suitable include those derived from the following genes: maize MAC1 (see, Sheridan (1996)  Genetics,  142:1009-1020); maize Cat3 (see, GenBank No. L05934; Abler (1993)  Plant Mol. Biol.,  22:10131-1038). Other promoters include the following  Arabidopsis  promoters: YP0039, YP0101, YP0102, YP0110, YP0117, YP0119, YP0137, DME, YP0285, and YP0212. Other promoters that may be useful include the following rice promoters: p530c10, pOsFIE2-2, pOsMEA, pOsYp102, and pOsYp285. 
     vi. Embryo Promoters 
     Regulatory regions that preferentially drive transcription in zygotic cells following fertilization can provide embryo-preferential expression. Most suitable are promoters that preferentially drive transcription in early stage embryos prior to the heart stage, but expression in late stage and maturing embryos is also suitable. Embryo-preferential promoters include the barley lipid transfer protein (Ltp1) promoter ( Plant Cell Rep  (2001) 20:647-654), YP0097, YP0107, YP0088, YP0143, YP0156, PT0650, PT0695, PT0723, PT0838, PT0879, and PT0740. 
     vii. Photosynthetic Tissue Promoters 
     Promoters active in photosynthetic tissue confer transcription in green tissues such as leaves and stems. Most suitable are promoters that drive expression only or predominantly in such tissues. Examples of such promoters include the ribulose-1,5-bisphosphate carboxylase (RbcS) promoters such as the RbcS promoter from eastern larch ( Larix laricina ), the pine cab6 promoter (Yamamoto et al.,  Plant Cell Physiol.,  35:773-778 (1994)), the Cab-1 promoter from wheat (Fejes et al.,  Plant Mol. Biol.,  15:921-932 (1990)), the CAB-1 promoter from spinach (Lubberstedt et al.,  Plant Physiol.,  104:997-1006 (1994)), the cab1R promoter from rice (Luan et al.,  Plant Cell,  4:971-981 (1992)), the pyruvate orthophosphate dikinase (PPDK) promoter from corn (Matsuoka et al.,  Proc. Natl. Acad. Sci. USA,  90:9586-9590 (1993)), the tobacco Lhcb1*2 promoter (Cerdan et al.,  Plant Mol. Biol.,  33:245-255 (1997)), the  Arabidopsis thaliana  SUC2 sucrose-H+ symporter promoter (Truernit et al.,  Planta,  196:564-570 (1995)), and thylakoid membrane protein promoters from spinach (psaD, psaF, psaE, PC, FNR, atpC, atpD, cab, rbcS). Other photosynthetic tissue promoters include PT0535, PT0668, PT0886, YP0144, YP0380 and PT0585. 
     viii. Vascular Tissue Promoters 
     Examples of promoters that have high or preferential activity in vascular bundles include YP0087, YP0093, YP0108, YP0022, and YP0080. Other vascular tissue-preferential promoters include the glycine-rich cell wall protein GRP 1.8 promoter (Keller and Baumgartner,  Plant Cell,  3(10):1051-1061 (1991)), the Commelina yellow mottle virus (CoYMV) promoter (Medberry et al.,  Plant Cell,  4(2):185-192 (1992)), and the rice tungro bacilliform virus (RTBV) promoter (Dai et al.,  Proc. Natl. Acad. Sci. USA,  101(2):687-692 (2004)). 
     ix. Inducible Promoters 
     Inducible promoters confer transcription in response to external stimuli such as chemical agents or environmental stimuli. For example, inducible promoters can confer transcription in response to hormones such as giberellic acid or ethylene, or in response to light or drought. Examples of drought-inducible promoters include YP0380, PT0848, YP0381, YP0337, PT0633, YP0374, PT0710, YP0356, YP0385, YP0396, YP0388, YP0384, PT0688, YP0286, YP0377, PD1367, and PD0901. Examples of nitrogen-inducible promoters include PT0863, PT0829, PT0665, and PT0886. Examples of shade-inducible promoters include PR0924 and PT0678. An example of a promoter induced by salt is rd29A (Kasuga et al. (1999) Nature Biotech 17: 287-291). 
     x. Basal Promoters 
     A basal promoter is the minimal sequence necessary for assembly of a transcription complex required for transcription initiation. Basal promoters frequently include a “TATA box” element that may be located between about 15 and about 35 nucleotides upstream from the site of transcription initiation. Basal promoters also may include a “CCAAT box” element (typically the sequence CCAAT) and/or a GGGCG sequence, which can be located between about 40 and about 200 nucleotides, typically about 60 to about 120 nucleotides, upstream from the transcription start site. 
     xi. Other Promoters 
     Other classes of promoters include, but are not limited to, shoot-preferential, callus-preferential, trichome cell-preferential, guard cell-preferential such as PT0678, tuber-preferential, parenchyma cell-preferential, and senescence-preferential promoters. Promoters designated YP0086, YP0188, YP0263, PT0758, PT0743, PT0829, YP0119, and YP0096, as described in the above-referenced patent applications, may also be useful. 
     xii. Other Regulatory Regions 
     A 5′ untranslated region (UTR) can be included in nucleic acid constructs described herein. A 5′ UTR is transcribed, but is not translated, and lies between the start site of the transcript and the translation initiation codon and may include the +1 nucleotide. A 3′ UTR can be positioned between the translation termination codon and the end of the transcript. UTRs can have particular functions such as increasing mRNA stability or attenuating translation. Examples of 3′ UTRs include, but are not limited to, polyadenylation signals and transcription termination sequences, e.g., a nopaline synthase termination sequence. 
     It will be understood that more than one regulatory region may be present in a recombinant polynucleotide, e.g., introns, enhancers, upstream activation regions, transcription terminators, and inducible elements. Thus, for example, more than one regulatory region can be operably linked to the sequence of a polynucleotide encoding a cold growth-modulating polypeptide. 
     Regulatory regions, such as promoters for endogenous genes, can be obtained by chemical synthesis or by subcloning from a genomic DNA that includes such a regulatory region. A nucleic acid comprising such a regulatory region can also include flanking sequences that contain restriction enzyme sites that facilitate subsequent manipulation. 
     IV. Transgenic Plants and Plant Cells 
     A. Transformation 
     The invention also features transgenic plant cells and plants comprising at least one recombinant nucleic acid construct described herein. A plant or plant cell can be transformed by having a construct integrated into its genome, i.e., can be stably transformed. Stably transformed cells typically retain the introduced nucleic acid with each cell division. A plant or plant cell can also be transiently transformed such that the construct is not integrated into its genome. Transiently transformed cells typically lose all or some portion of the introduced nucleic acid construct with each cell division such that the introduced nucleic acid cannot be detected in daughter cells after a sufficient number of cell divisions. Both transiently transformed and stably transformed transgenic plants and plant cells can be useful in the methods described herein. 
     Transgenic plant cells used in methods described herein can constitute part or all of a whole plant. Such plants can be grown in a manner suitable for the species under consideration, either in a growth chamber, a greenhouse, or in a field. Transgenic plants can be bred as desired for a particular purpose, e.g., to introduce a recombinant nucleic acid into other lines, to transfer a recombinant nucleic acid to other species, or for further selection of other desirable traits. Alternatively, transgenic plants can be propagated vegetatively for those species amenable to such techniques. As used herein, a transgenic plant also refers to progeny of an initial transgenic plant, as long as the progeny inherits the transgene. Seeds produced by a transgenic plant can be grown and then selfed (or outcrossed and selfed) to obtain seeds homozygous for the nucleic acid construct. 
     Transgenic plants can be grown in suspension culture, or tissue or organ culture. For the purposes of this invention, solid and/or liquid tissue culture techniques can be used. When using solid medium, transgenic plant cells can be placed directly onto the medium or can be placed onto a filter that is then placed in contact with the medium. When using liquid medium, transgenic plant cells can be placed onto a flotation device, e.g., a porous membrane that contacts the liquid medium. A solid medium can be, for example, Murashige and Skoog (MS) medium containing agar and a suitable concentration of an auxin, e.g., 2,4-dichlorophenoxyacetic acid (2,4-D), and a suitable concentration of a cytokinin, e.g., kinetin. 
     When transiently transformed plant cells are used, a reporter sequence encoding a reporter polypeptide having a reporter activity can be included in the transformation procedure and an assay for reporter activity or expression can be performed at a suitable time after transformation. A suitable time for conducting the assay typically is about 1-21 days after transformation, e.g., about 1-14 days, about 1-7 days, or about 1-3 days. The use of transient assays is particularly convenient for rapid analysis in different species, or to confirm expression of a heterologous cold growth-modulating polypeptide whose expression has not previously been confirmed in particular recipient cells. 
     Techniques for introducing nucleic acids into monocotyledonous and dicotyledonous plants are known in the art, and include, without limitation,  Agrobacterium -mediated transformation, viral vector-mediated transformation, electroporation and particle gun transformation, e.g., U.S. Pat. Nos. 5,538,880; 5,204,253; 6,329,571 and 6,013,863. If a cell or cultured tissue is used as the recipient tissue for transformation, plants can be regenerated from transformed cultures if desired, by techniques known to those skilled in the art. 
     B. Screening/selection 
     A population of transgenic plants can be screened and/or selected for those members of the population that have a trait or phenotype conferred by expression of the transgene. For example, a population of progeny of a single transformation event can be screened for those plants having a desired level of expression of a cold tolerance-modulating polypeptide or nucleic acid. Physical and biochemical methods can be used to identify expression levels. These include Southern analysis or PCR amplification for detection of a polynucleotide; Northern blots, 51 RNase protection, primer-extension, or RT-PCR amplification for detecting RNA transcripts; enzymatic assays for detecting enzyme or ribozyme activity of polypeptides and polynucleotides; and protein gel electrophoresis, Western blots, immunoprecipitation, and enzyme-linked immunoassays to detect polypeptides. Other techniques such as in situ hybridization, enzyme staining, and immunostaining also can be used to detect the presence or expression of polypeptides and/or polynucleotides. Methods for performing all of the referenced techniques are known. As an alternative, a population of plants comprising independent transformation events can be screened for those plants having a desired trait, such as a modulated level of growth under cold conditions. Selection and/or screening can be carried out over one or more generations, and/or in more than one geographic location. In some cases, transgenic plants can be grown and selected under conditions which induce a desired phenotype or are otherwise necessary to produce a desired phenotype in a transgenic plant. In addition, selection and/or screening can be applied during a particular developmental stage in which the phenotype is expected to be exhibited by the plant. Selection and/or screening can be carried out to choose those transgenic plants having a statistically significant difference in a growth level under cold conditions relative to a control plant that lacks the transgene. Selected or screened transgenic plants have an altered phenotype as compared to a corresponding control plant, as described in the “Transgenic Plant Phenotypes” section herein. 
     C. Plant Species 
     The polynucleotides and vectors described herein can be used to transform a number of monocotyledonous and dicotyledonous plants and plant cell systems, including species from one of the following families: Acanthaceae, Alliaceae, Alstroemeriaceae, Amaryllidaceae, Apocynaceae, Arecaceae, Asteraceae, Berberidaceae, Bixaceae, Brassicaceae, Bromeliaceae, Cannabaceae, Caryophyllaceae, Cephalotaxaceae, Chenopodiaceae, Colchicaceae, Cucurbitaceae, Dioscoreaceae, Ephedraceae, Erythroxylaceae, Euphorbiaceae, Fabaceae, Lamiaceae, Linaceae, Lycopodiaceae, Malvaceae, Melanthiaceae, Musaceae, Myrtaceae, Nyssaceae, Papaveraceae, Pinaceae, Plantaginaceae, Poaceae, Rosaceae, Rubiaceae, Salicaceae, Sapindaceae, Solanaceae, Taxaceae, Theaceae, or Vitaceae. 
     Suitable species may include members of the genus  Abelmoschus, Abies, Acer, Agrostis, Allium, Alstroemeria, Ananas, Andrographis, Andropogon, Artemisia, Arundo, Atropa, Berberis, Beta, Bixa, Brassica, Calendula, Camellia, Camptotheca, Cannabis, Capsicum, Carthamus, Catharanthus, Cephalotaxus, Chrysanthemum, Cinchona, Citrullus, Coffea, Colchicum, Coleus, Cucumis, Cucurbita, Cynodon, Datura, Dianthus, Digitalis, Dioscorea, Elaeis, Ephedra, Erianthus, Erythroxylum, Eucalyptus, Festuca, Fragaria, Galanthus, Glycine, Gossypium, Helianthus, Hevea, Hordeum, Hyoscyamus, Jatropha, Lactuca, Linum, Lolium, Lupinus, Lycopersicon, Lycopodium, Manihot, Medicago, Mentha, Miscanthus, Musa, Nicotiana, Oryza, Panicum, Papaver, Parthenium, Pennisetum, Petunia, Phalaris, Phleum, Pinus, Poa, Poinsettia, Populus, Rauwolfia, Ricinus, Rosa, Saccharum, Salix, Sanguinaria, Scopolia, Secale, Solanum, Sorghum, Spartina, Spinacea, Tanacetum, Taxus, Theobroma, Triticosecale, Triticum, Uniola, Veratrum, Vinca, Vitis , and  Zea.    
     Suitable species include  Panicum  spp.,  Sorghum  spp.,  Miscanthus  spp.,  Saccharum  spp.,  Erianthus  spp.,  Populus  spp.,  Andropogon gerardii  (big bluestem),  Pennisetum purpureum  (elephant grass),  Phalaris arundinacea  (reed canarygrass),  Cynodon dactylon  (bermudagrass),  Festuca arundinacea  (tall fescue),  Spartina pectinata  (prairie cord-grass),  Medicago sativa  (alfalfa),  Arundo donax  (giant reed),  Secale cereale  (rye),  Salix  spp. (willow),  Eucalyptus  spp. (eucalyptus),  Triticosecale  (triticum—wheat X rye) and bamboo. 
     Suitable species also include  Helianthus annuus  (sunflower),  Carthamus tinctorius  (safflower),  Jatropha curcas  (jatropha),  Ricinus communis  (castor),  Elaeis guineensis  (palm),  Linum usitatissimum  (flax), and  Brassica juncea.    
     Suitable species also include  Beta vulgaris  (sugarbeet), and  Manihot esculenta  (cassava) 
     Suitable species also include  Lycopersicon esculentum  (tomato),  Lactuca sativa  (lettuce),  Musa paradisiaca  (banana),  Solanum tuberosum  (potato),  Brassica oleracea  (broccoli, cauliflower, brusselsprouts),  Camellia sinensis  (tea),  Fragaria ananassa  (strawberry),  Theobroma cacao  (cocoa),  Coffea arabica  (coffee),  Vitis vinifera  (grape),  Ananas comosus  (pineapple),  Capsicum  annum (hot &amp; sweet pepper),  Allium cepa  (onion),  Cucumis melo  (melon),  Cucumis sativus  (cucumber),  Cucurbita maxima  (squash),  Cucurbita moschata  (squash),  Spinacea oleracea  (spinach),  Citrullus lanatus  (watermelon),  Abelmoschus esculentus  (okra), and  Solanum melongena  (eggplant). 
     Suitable species also include  Papaver somniferum  (opium poppy),  Papaver orientale, Taxus baccata, Taxus brevifolia, Artemisia annua, Cannabis sativa, Camptotheca acuminate, Catharanthus roseus, Vinca rosea, Cinchona officinalis, Colchicum autumnale, Veratrum californica, Digitalis lanata, Digitalis purpurea, Dioscorea  spp.,  Andrographis paniculata, Atropa belladonna, Datura stomonium, Berberis  spp.,  Cephalotaxus  spp.,  Ephedra sinica, Ephedra  spp.,  Erythroxylum coca, Galanthus wornorii, Scopolia  spp.,  Lycopodium serratum  (= Huperzia serrata ),  Lycopodium  spp.,  Rauwolfia serpentina, Rauwolfia  spp.,  Sanguinaria canadensis, Hyoscyamus  spp.,  Calendula officinalis, Chrysanthemum parthenium, Coleus forskohlii, and Tanacetum parthenium.    
     Suitable species also include  Parthenium argentatum  (guayule),  Hevea  spp. (rubber),  Mentha spicata  (mint),  Mentha piperita  (mint),  Bixa orellana , and  Alstroemeria  spp. 
     Suitable species also include  Rosa  spp. (rose),  Dianthus caryophyllus  (carnation),  Petunia  spp. (petunia) and  Poinsettia pulcherrima  (poinsettia). 
     Suitable species also include  Nicotiana tabacum  (tobacco),  Lupinus albus  (lupin),  Uniola paniculata  (oats), bentgrass ( Agrostis  spp.),  Populus tremuloides  (aspen),  Pinus  spp. (pine),  Abies  spp. (fir),  Acer  spp. (maple,  Hordeum vulgare  (barley),  Poa pratensis  (bluegrass),  Lolium  spp. (ryegrass) and  Phleum pratense  (timothy). 
     Thus, the methods and compositions can be used over a broad range of plant species, including species from the dicot genera  Brassica, Carthamus, Glycine, Gossypium, Helianthus, Jatropha, Parthenium, Populus , and  Ricinus ; and the monocot genera  Elaeis, Festuca, Hordeum, Lolium, Oryza, Panicum, Pennisetum, Phleum, Poa, Saccharum, Secale, Sorghum, Triticosecale, Triticum , and  Zea . In some embodiments, a plant is a member of the species  Panicum virgatum  (switchgrass),  Sorghum bicolor  (sorghum, sudangrass),  Miscanthus giganteus  (miscanthus),  Saccharum  sp. (energycane),  Populus balsamifera  (poplar),  Zea mays  (corn),  Glycine max  (soybean),  Brassica napus  (canola),  Triticum aestivum  (wheat),  Gossypium hirsutum  (cotton),  Oryza sativa  (rice),  Helianthus annuus  (sunflower),  Medicago sativa  (alfalfa),  Beta vulgaris  (sugarbeet), or  Pennisetum glaucum  (pearl millet). 
     In certain embodiments, the polynucleotides and vectors described herein can be used to transform a number of monocotyledonous and dicotyledonous plants and plant cell systems, wherein such plants are hybrids of different species or varieties of a species (e.g.,  Saccharum  sp. X  Miscanthus  sp.). 
     D. Transgenic Plant Phenotypes 
     In some embodiments, a plant in which expression of a cold tolerance-modulating polypeptide is modulated can have increased levels of cold tolerance and/or biomass in vegetative tissues. Cold tolerance can be measured by means well know to those of skill in the art, including, but not limited to, seedling survival, decreased photosynthesis and membrane damage (measured by electrolyte leakage), seedling area, yield, and or biomass. For example, a cold tolerance-modulating polypeptide described herein can be expressed in a transgenic plant, resulting in increased levels of cold tolerance and/or biomass. The cold tolerance level can be increased by at least 0.25 percent, e.g., 0.25, 0.5, 0.75, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100 or more than 100 percent, as compared to the cold tolerance level in a corresponding control plant that does not express the transgene. In some embodiments, a plant in which expression of a cold tolerance-modulating polypeptide is modulated can have increased levels of biomass. The biomass level can be increased by at least 0.25 percent, e.g., 0.25, 0.5, 0.75, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100 or more than 100 percent, as compared to the biomass level in a corresponding control plant that does not express the transgene. In some embodiments, a plant in which expression of a cold tolerance-modulating polypeptide is modulated can be exposed to cold for one or more periods of time that may vary depending on climatic conditions. For example, for periods of about ½ hour, 1 hour, 3 hours, 6 hours, 12 hours, 1 day, 3 days, 5 days, 10 days, 1 month, 3 months, 6 months, 12 months, or the entire lifespan of such a plant. 
     Increases in cold tolerance in such plants can provide improved nutritional quantity and content in geographic locales where cold affects plants. Increases in cold tolerance in such plants can be useful in situations where plant parts such as, but not limited to, seeds, tubers, stems, leaves or roots are harvested for human or animal consumption. 
     Typically, a difference in the level of cold tolerance in a transgenic plant or cell relative to a control plant or cell is considered statistically significant at p≦0.05 with an appropriate parametric or non-parametric statistic, e.g., Chi-square test, Student&#39;s t-test, Mann-Whitney test, or F-test. In some embodiments, a difference in the level of cold tolerance is statistically significant at p&lt;0.01, p&lt;0.005, or p&lt;0.001. A statistically significant difference in, for example, the level of cold tolerance in a transgenic plant compared to the amount in cells of a control plant indicates that the recombinant nucleic acid present in the transgenic plant results in altered cold tolerance levels. 
     The phenotype of a transgenic plant is evaluated relative to a control plant. A plant is said “not to express” a polypeptide when the plant exhibits less than 10%, e.g., less than 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.01%, or 0.001%, of the amount of polypeptide or mRNA encoding the polypeptide exhibited by the plant of interest. Expression can be evaluated using methods including, for example, RT-PCR, Northern blots, S1 RNase protection, primer extensions, Western blots, protein gel electrophoresis, immunoprecipitation, enzyme-linked immunoassays, chip assays, and mass spectrometry. It should be noted that if a polypeptide is expressed under the control of a tissue-preferential or broadly expressing promoter, expression can be evaluated in the entire plant or in a selected tissue. Similarly, if a polypeptide is expressed at a particular time, e.g., at a particular time in development or upon induction, expression can be evaluated selectively at a desired time period. 
     V. Plant Breeding 
     Genetic polymorphisms are discrete allelic sequence differences in a population. Typically, an allele that is present at 1% or greater is considered to be a genetic polymorphism. The discovery that polypeptides disclosed herein can modulate cold tolerance is useful in plant breeding, because genetic polymorphisms exhibiting a degree of linkage with loci for such polypeptides are more likely to be correlated with variation in a cold tolerance trait. For example, genetic polymorphisms linked to the loci for such polypeptides are more likely to be useful in marker-assisted breeding programs to create lines having a desired modulation in the cold tolerance trait. 
     Thus, one aspect of the invention includes methods of identifying whether one or more genetic polymorphisms are associated with variation in a cold tolerance trait. Such methods involve determining whether genetic polymorphisms in a given population exhibit linkage with the locus for one of the polypeptides depicted in  FIG. 1  or  2  and/or a functional homolog thereof, such as, but not limited to, those identified in the Sequence Listing of this application. The correlation is measured between variation in the cold tolerance trait in plants of the population and the presence of the genetic polymorphism(s) in plants of the population, thereby identifying whether or not the genetic polymorphism(s) are associated with variation for the trait. If the presence of a particular allele is statistically significantly correlated with a desired modulation in the cold tolerance trait, the allele is associated with variation for the trait and is useful as a marker for the trait. If, on the other hand, the presence of a particular allele is not significantly correlated with the desired modulation, the allele is not associated with variation for the trait and is not useful as a marker. 
     Such methods are applicable to populations containing the naturally occurring endogenous polypeptide rather than an exogenous nucleic acid encoding the polypeptide, i.e., populations that are not transgenic for the exogenous nucleic acid. It will be appreciated, however, that populations suitable for use in the methods may contain a transgene for another, different trait, e.g., herbicide resistance. 
     Genetic polymorphisms that are useful in such methods include simple sequence repeats (SSRs, or microsatellites), rapid amplification of polymorphic DNA (RAPDs), single nucleotide polymorphisms (SNPs), amplified fragment length polymorphisms (AFLPs) and restriction fragment length polymorphisms (RFLPs). SSR polymorphisms can be identified, for example, by making sequence specific probes and amplifying template DNA from individuals in the population of interest by PCR. If the probes flank an SSR in the population, PCR products of different sizes will be produced. See, e.g., U.S. Pat. No. 5,766,847. Alternatively, SSR polymorphisms can be identified by using PCR product(s) as a probe against Southern blots from different individuals in the population. See, U. H. Refseth et al., (1997) Electrophoresis 18: 1519. The identification of RFLPs is discussed, for example, in Alonso-Blanco et al. (Methods in Molecular Biology, vol. 82, “ Arabidopsis  Protocols”, pp. 137-146, J. M. Martinez-Zapater and J. Salinas, eds., c. 1998 by Humana Press, Totowa, N.J.); Burr (“Mapping Genes with Recombinant Inbreds”, pp. 249-254, in Freeling, M. and V. Walbot (Ed.), The Maize Handbook, c. 1994 by Springer-Verlag New York, Inc.: New York, N.Y., USA; Berlin Germany; Burr et al. Genetics (1998) 118: 519; and Gardiner, J. et al., (1993) Genetics 134: 917). The identification of AFLPs is discussed, for example, in EP 0 534 858 and U.S. Pat. No. 5,878,215. 
     In some embodiments, the methods are directed to breeding a plant line. Such methods use genetic polymorphisms identified as described above in a marker assisted breeding program to facilitate the development of lines that have a desired alteration in the cold tolerance trait. Once a suitable genetic polymorphism is identified as being associated with variation for the trait, one or more individual plants are identified that possess the polymorphic allele correlated with the desired variation. Those plants are then used in a breeding program to combine the polymorphic allele with a plurality of other alleles at other loci that are correlated with the desired variation. Techniques suitable for use in a plant breeding program are known in the art and include, without limitation, backcrossing, mass selection, pedigree breeding, bulk selection, crossing to another population and recurrent selection. These techniques can be used alone or in combination with one or more other techniques in a breeding program. Thus, each identified plants is selfed or crossed a different plant to produce seed which is then germinated to form progeny plants. At least one such progeny plant is then selfed or crossed with a different plant to form a subsequent progeny generation. The breeding program can repeat the steps of selfing or outcrossing for an additional 0 to 5 generations as appropriate in order to achieve the desired uniformity and stability in the resulting plant line, which retains the polymorphic allele. In most breeding programs, analysis for the particular polymorphic allele will be carried out in each generation, although analysis can be carried out in alternate generations if desired. 
     In some cases, selection for other useful traits is also carried out, e.g., selection for fungal resistance or bacterial resistance. Selection for such other traits can be carried out before, during or after identification of individual plants that possess the desired polymorphic allele. 
     VI. Articles of Manufacture 
     Transgenic plants provided herein have various uses in the agricultural and energy production industries. For example, transgenic plants described herein can be used to make animal feed and food products. Such plants, however, are often particularly useful as a feedstock for energy production. 
     Transgenic plants described herein often produce higher yields of grain and/or biomass per hectare, relative to control plants that lack the exogenous nucleic acid. In some embodiments, such transgenic plants provide equivalent or even increased yields of grain and/or biomass per hectare relative to control plants when grown under conditions of reduced inputs such as fertilizer and/or water. Thus, such transgenic plants can be used to provide yield stability at a lower input cost and/or under environmentally stressful conditions such as drought. In some embodiments, plants described herein have a composition that permits more efficient processing into free sugars, and subsequently ethanol, for energy production. In some embodiments, such plants provide higher yields of ethanol, butanol, other biofuel molecules, and/or sugar-derived co-products per kilogram of plant material, relative to control plants. Such processing efficiencies are believed to be derived from the chemical composition of the plant material. By providing higher yields at an equivalent or even decreased cost of production relative to control plants that do not have increased levels of cold tolerance, the transgenic plants described herein improve profitability for farmers and processors as well as decrease costs to consumers. 
     Seeds from transgenic plants described herein can be conditioned and bagged in packaging material by means known in the art to form an article of manufacture. Packaging material such as paper and cloth are well known in the art. A package of seed can have a label, e.g., a tag or label secured to the packaging material, a label printed on the packaging material, or a label inserted within the package, that describes the nature of the seeds therein. 
     The invention will be further described in the following examples, which do not limit the scope of the invention described in the claims. 
     VII. Examples 
     Example 1 
     Transgenic  Arabidopsis  Plants 
     The following symbols are used in the Examples with respect to  Arabidopsis  transformation: T 1 : first generation transformant; T 2 : second generation, progeny of self-pollinated T 1  plants; T 3 : third generation, progeny of self-pollinated T 2  plants; T 4 : fourth generation, progeny of self-pollinated T 3  plants. Independent transformations are referred to as events. 
     The following is a list of nucleic acids that were isolated from  Arabidopsis thaliana  plants, Ceres Clone ID: 10510, Ceres Clone ID: 3204, Ceres Annot ID: 827264, Ceres Annot ID: 833191, Ceres Clone ID: 567548, Ceres cDNA ID no. 23507179, Ceres ANNOT ID no.1450474, Ceres CLONE ID no. 1064543, Ceres Clone ID: 8965, Ceres Clone ID: 2900, Ceres Clone ID: 552911, Ceres Clone ID: 555598, Ceres Annot ID: 864797, Ceres Annot ID: 875863, Ceres Clone ID: 830572, Ceres Clone ID: 36243, Ceres Clone ID: 34358, Ceres Clone ID: 250899, Ceres Annot ID: 861093, Ceres Clone ID: 198760, Ceres Clone ID: 99920, Ceres Annot ID: 840521, Ceres Annot ID: 854792, Ceres Clone ID: 855827, Ceres Annot ID: 850305, Ceres Annot ID: 840158, Ceres Clone ID: 36243, Ceres Annot ID: 850305, Ceres Annot ID: 849805, Ceres Annot ID: 886125, Ceres Annot ID: 827093, Ceres Annot ID: 846607, Ceres Annot ID: 849981, Ceres Clone ID: 14973, Ceres Annot ID: 851645, Ceres Annot ID: 857770, Ceres Annot ID: 1460704, and Ceres Annot ID: 576111 (SEQ ID NOs: 71, 72, 73, 75, 80, 99, 101, 116, 128, 134, 144, 151, 159, 163, 168, 171, 173, 177, 191, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, 279, and 119). 
     Each isolated nucleic acid described above was cloned into a Ti plasmid vector containing a phosphinothricin acetyltransferase gene which confers Finale™ resistance to transformed plants. A Ti plasmid vector useful for these constructs is CRS 338. Unless otherwise indicated, each Ceres Clone and/or Seedline derived from a Clone is in the sense orientation relative to either the 35S promoter in a Ti plasmid. Wild-type  Arabidopsis thaliana  ecotype Wassilewskija (Ws) plants were transformed separately with each construct. The transformations were performed essentially as described in Bechtold et al.,  C.R. Acad. Sci. Paris,  316:1194-1199 (1993). 
     The presence of each vector containing a nucleic acid described herein in the respective transgenic  Arabidopsis  line transformed with the vector was confirmed by Finale™ resistance, PCR amplification from green leaf tissue extract, and/or sequencing of PCR products. As controls, wild-type  Arabidopsis  ecotype Ws plants were transformed with an empty vector. 
     Example 2 
     Screening for Cold Tolerance in Transgenic Plants 
     How plants respond to stress in the environment dictates their ability to survive and reproduce. There are probably many mechanisms by which plants regulate the temperatures under which they will germinate (Lu and Hills, 2003). A number of polynucleotides that result in stress tolerance when over-expressed have been identified in model species such as  Arabidopsis.    
     Over-expression of these polynucleotides could be useful for increasing low temperature, chilling or cold tolerance in crops. Assays described here focus on low temperature, chilling or cold tolerance in seedlings. The ability to germinate and grow under low temperature, chilling or cold, and wet conditions would allow a longer growing season and mitigate damage caused by unexpected low temperature, chilling or cold periods. If this trait is recapitulated in crops overexpressing these polynucleotides, the result could be very valuable in agriculture in many crops and environments and make a significant contribution to sustainable farming. Furthermore, low temperature, chilling or cold tolerance may be modulated by expressing these polynucleotides under the control of a low temperature, chilling or cold inducible promoter. 
     1. Cold Growth Superpool Screen 
     Plates of solidified agar MS medium are prepared for the screen as follows. One liter of medium is prepared by mixing 2.15 g of MS basal salt mixture (from Phytotech M524) and 7 g of agar (from EM Science, 1.01614.1000) in water, and adjusting the pH to 5.7 with a 10N KOH solution. After autoclaving, 45 ml of media are transferred under sterile conditions per 100 mm square×15 mm deep plate. 
     Individual superpool and control seeds are sterilized in a 30% bleach solution for 5 minutes. Seeds are then rinsed repeatedly with sterile water to eliminate all bleach solution. Seeds are plated using a COPAS™ robot (Union Biometrica, Holliston, Mass.) at a density of 72 seeds per plate. The plates are wrapped with vent tape and transferred to a dark 4° C. refrigerator for 3 days to promote uniform germination. The plates are then placed horizontally in a Conviron growth chamber set at 22° C., 16:8 hour light:dark cycle, 70% humidity with fluorescent lamps emitting a light intensity of ˜100 μEinsteins. Normal growth is allowed to occur for 3-5 days. At end of 3-5 days of growth, images of the plates are scanned using an Epson perfection 4870 scanner. Then, cold-growth treatment is applied for 1-3 weeks. Accordingly, plates are transferred in a horizontal position to an 8′C Conviron chamber under constant light at ˜100 μEinsteins. After a defined number of days of cold-growth treatment, for example 7 or 14, the plates are scanned again. The WinRhizo software program (Regent Instruments Inc., Canada) is used to determine the area for each seedling from the scanned images. 
     Individual seedlings that perform better in the cold growth screen are identified by visual inspection for those showing obvious morphological differences and by statistical analysis of the seedling area data. DNA from these candidate seedlings is extracted and the transgene amplified using PCR. The PCR product is sequenced to determine the identity of the transgene and consequently the ME line from which the candidate is derived. 
     2. Cold Growth Assay 
     The cold growth assay is used to validate candidate misexpression (ME) lines obtained from screens for enhanced growth under cold conditions. This procedure allows a high-throughput methodology for assessing transgenic  Arabidopsis  candidates that have germinated at normal temperature (22° C.) and light (˜100 to 200 μEinsteins) in a walk-in growth chamber on agar solidified MS medium before transfer to cold temperature. It relies on the ability to discriminate between seedlings that have become significantly larger during cold growth than controls by imaging the seedlings when they are transferred to the cold and then periodically thereafter under cold growth conditions. 
     Plate preparation for the cold growth assay and the growth conditions are the same as those described for the cold growth screen as described above. Seeds from independent transformation events for each ME line are bleach sterilized and then plated at a density of 40 seeds per plate (30 seeds from the event and 10 wild-type control seeds). After cold-growth treatment, the seedlings are then FINALE®-treated to identify the plants carrying the ME vector. 
     Cold growth is characterized by statistical analysis as follows. The control population is the internal non-transgenic segregants for that particular event. When there are not enough internal non-transgenic segregants for an event, a pool of all non-transgenic segregants from all events associated with that ME line is used (i.e. when non-transgenics are less than five for the event or the event appears to be homozygous). Pooling is only done for events associated with the same ME line and within an experiment (an experiment is the set of plates with a common sow date). Thus in the final analysis, the pooled control population may be different for generations T 2  and T 3 . 
     The WinRhizo software program (Regent Instruments Inc., Canada) is used to determine the area for each seedling. The change in area is calculated for a defined number of days of treatment. A one-tailed t-test is used to compare change in area and the mean size of the transgenic seedlings within an event to the internal non-transgenic segregants. Significance is assessed at an α-value of 0.05. 
     Example 3 
     Results for ME12469 (SEQ ID NO: 79) and Other SAUR Family Transgenic Events 
     ME12469 was Identified from a Superpool Screen for Growth Under Cold Conditions. 
     A Megapool consisting of five superpools (10,000 seeds) was screened for seedlings that grew more vigorously than controls after transfer to cold conditions as described above. Eighteen candidates were chosen from this Megapool. ME12469 was represented four times in this set and was identified as a member of the SAUR gene family. 
     Three Events of ME12469 Showed Significant Tolerance Under Cold Conditions in Two Generations. 
     In this study, the seedling area of transgenic plants within a seed line was compared to that of non-transgenic segregants within the same seed line after 18 days of growth at 8° C. Ten events of ME12469 were analyzed as described in the Cold Growth Assay. Three Events, −02, −07 and −09, were significant in both generations at p≦0.05 using a one-tailed t-test assuming unequal variance (Table 3-1). Since the T 3  generation seed lines of Events −01, −05 and −10 did not segregate any non-transgenic seedlings, comparisons to internal controls could not be made and the data is not shown. However, in each case, the transgenic seedlings were significantly larger than the pooled non-transgenic segregants from the other Events of ME12469 sown in the experiment (data not shown). 
     The transgenic plants were visibly larger and lighter in color than the controls. Under cold conditions, seedlings typically become darker, presumably due to the accumulation of anthocyanin. The lighter color exhibited by ME12469 seedlings suggests a decrease in this stress response. ME12469 plants grown under standard conditions in soil did not appear different in color than controls. 
     
       
         
           
               
             
               
                 TABLE 3-1 
               
             
            
               
                   
               
               
                 T-test comparison of seedling area between transgenic seedlings and control 
               
               
                 non-transgenic segregants after 18 days at 8° C. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 Control Non- 
                   
               
               
                   
                 Event- 
                 Transgenic 
                 Transgenics a   
                 t-test 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Events 
                 Gen 
                 Avg 
                 SE 
                 N 
                 Avg 
                 SE 
                 N 
                 p-value 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 ME12469-01 
                 01-T2 
                 0.2844 
                 0.0106 
                 13 
                 0.2116 
                 0.0116 
                 17 
                 3.75E−05 
               
               
                 ME12469-01 
                 01-T2 
                 0.2512 
                 0.0145 
                 18 
                 0.2108 
                 0.0120 
                 12 
                 0.0201 
               
               
                 ME12469-02 
                 02-T2 
                 0.2501 
                 0.0193 
                 24 
                 0.1663 
                 0.0215 
                 4 
                 0.0038 
               
               
                 ME12469-02 
                 02-T2 
                 0.3185 
                 0.0093 
                 25 
                 0.2598 
                 0.0083 
                 4 
                 3.17E−05 
               
               
                 ME12469-02-01 
                 02-T3 
                 0.2512 
                 0.0103 
                 25 
                 0.2023 
                 0.0124 
                 5 
                 0.0026 
               
               
                 ME12469-05 
                 05-T2 
                 0.1294 
                 0.0071 
                 25 
                 0.1027 
                 0.0102 
                 4 
                 0.0201 
               
               
                 ME12469-07 
                 07-T2 
                 0.1508 
                 0.0103 
                 21 
                 0.1150 
                 0.0112 
                 9 
                 0.0130 
               
               
                 ME12469-07-02 
                 07-T3 
                 0.2916 
                 0.0089 
                 22 
                 0.2203 
                 0.0240 
                 8 
                 0.0047 
               
               
                 ME12469-07-04 
                 07-T3 
                 0.2923 
                 0.0119 
                 18 
                 0.2622 
                 0.0110 
                 12 
                 0.0375 
               
               
                 ME12469-09 
                 09-T2 
                 0.2015 
                 0.0123 
                 18 
                 0.1297 
                 0.0105 
                 8 
                 8.36E−05 
               
               
                 ME12469-09-02 
                 09-T3 
                 0.3220 
                 0.0215 
                 21 
                 0.2397 
                 0.0270 
                 6 
                 0.0124 
               
               
                 ME12469-10 
                 10-T2 
                 0.3670 
                 0.0159 
                 19 
                 0.2894 
                 0.0157 
                 9 
                 0.0009 
               
               
                   
               
               
                   a Transgenic seedlings were compared to non-transgenic segregants within a seed line. 
               
            
           
         
       
     
     Other SAUR Gene Family Members Showed Significant Tolerance Under Cold Conditions. 
     In addition to selecting gene candidates from the Cold Growth Superpool Screen, candidate genes were selected for analysis based on similarity to other SAUR genes that conferred cold tolerance. Analysis of seedling area indicated that eighteen SAUR homolog transgenic lines were significant at p≦0.05 using a one-tailed t-test assuming unequal variance (Table 3-2). 
     The transgenic plants were visibly larger and lighter in color than the controls. Under cold conditions, seedlings typically become darker, presumably due to the accumulation of anthocyanin. The lighter colored seedlings suggested a decrease in this stress response. Transgenic plants grown under standard conditions in soil did not appear different in color than controls. 
     
       
         
           
               
             
               
                 TABLE 3-2 
               
             
            
               
                   
               
               
                 Cold tolerance results for transgenic  Arabidopsis   
               
               
                 lines expressing exemplary SAUR family genes. 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Standard 
                 Cold 
               
               
                 Locus 
                 Line 
                 Temp 
                 Temp a   
               
               
                   
               
               
                 AT3G12830 
                 ME25264 (SEQ ID NO: 245) 
                 + 
                 + 
               
               
                 AT5G42410 
                 ME25217 (SEQ ID NO: 246) 
                 + 
                 + 
               
               
                 AT1G17345 
                 ME14040 (SEQ ID NO: 159) 
                 + 
                 + 
               
               
                 AT1G72430 
                 ME02192 (SEQ ID NO: 244) 
                 ∘ 
                 + 
               
               
                   
                 ME14195 (SEQ ID NO: 244) 
                 ∘ 
                 + 
               
               
                 AT5G50760 
                 ME25456 (SEQ ID NO: 247) 
                 ∘ 
                 + 
               
               
                 AT2G36210 
                 ME14045 (SEQ ID NO: 191) 
                 − 
                 + 
               
               
                 AT4G09530 
                 ME25206 (SEQ ID NO: 255) 
                 ∘ 
                 + 
               
               
                 AT2G37030 
                 ME25221 (SEQ ID NO: 248) 
                 + 
                 + 
               
               
                 AT1G20470 
                 ME06899 (SEQ ID NO: 177) 
                 ∘ 
                 + 
               
               
                 AT3G09870 
                 ME25219 (SEQ ID NO: 249) 
                 + 
                 + 
               
               
                 AT2G28085 
                 ME02978 (SEQ ID NO: 171) 
                 ∘ 
                 + 
               
               
                 AT2G21220 
                 ME06788 (SEQ ID NO: 134) 
                 + 
                 + 
               
               
                   
                 ME25207 (SEQ ID NO: 134) 
                 + 
                 + 
               
               
                 AT4G38860 
                 ME25211 (SEQ ID NO: 251) 
                 + 
                 + 
               
               
                 AT2G16580 
                 ME25205 (SEQ ID NO: 254) 
                 ∘ 
                 + 
               
               
                 AT4G36110 
                 ME25209 (SEQ ID NO: 256) 
                 ∘ 
                 + 
               
               
                 AT5G66260 
                 ME25243 (SEQ ID NO: 259) 
                 ∘ 
                 + 
               
               
                 AT4G13790 
                 ME00339 (SEQ ID NO: 128) 
                 + 
                 + 
               
               
                 AT4G38850 
                 ME07184 (SEQ ID NO: 257) 
                 ∘ 
                 + 
               
               
                 AT4G34790 
                 ME12469 (SEQ ID NO: 80) 
                 + 
                 + 
               
               
                 AT4G34770 
                 ME10609 (SEQ ID NO: 99) 
                 ∘ 
                 + 
               
               
                 AT1G75590 
                 ME05746 (SEQ ID NO: 173) 
                 ∘ 
                 + 
               
               
                 AT5G10990 
                 ME25265 (SEQ ID NO: 258) 
                 ∘ 
                 + 
               
               
                 AT4G34750 
                 ME25266 (SEQ ID NO: 252) 
                 − 
                 + 
               
               
                 AT2G24400 
                 ME10877 (SEQ ID NO: 144) 
                 ∘ 
                 + 
               
               
                 AT2G45210 
                 ME10853 (SEQ ID NO: 168) 
                 ∘ 
                 + 
               
               
                 AT3G60690 
                 ME16427 (SEQ ID NO: 163) 
                 ∘ 
                 + 
               
               
                 AT2G46690 
                 ME12470 (SEQ ID NO: 151) 
                 + 
                 + 
               
               
                 AT5G53590 
                 ME20371 (SEQ ID NO: 253) 
                 ∘ 
                 + 
               
               
                 Poplar locus 
                 ME25691 (SEQ ID NO: 101) 
                 ∘ 
                 + 
               
               
                 Poplar locus 
                 ME25692 (SEQ ID NO: 279) 
                 ∘ 
                 + 
               
               
                 Maize locus 
                 ME24962 (SEQ ID NO: 116) 
                 ∘ 
                 + 
               
               
                   
               
               
                   a “+” indicates significantly positive; 
               
               
                 “−” indicates significantly negative; and 
               
               
                 “∘” indicates no phenotype. 
               
            
           
         
       
     
     Example 4 
     Results for ME09090 (SEQ ID NO:119) Events 
     ME09090 was Identified from a Superpool Screen for Growth Under Cold Conditions. 
     A megapool consisting of twenty superpools (10,000 seeds) was screened for seedlings that grew more vigorously than controls after transfer to cold conditions as described above. One hundred candidates were chosen from this Megapool. ME09090 was represented one time in this set. 
     Two Events of ME09090 Showed Significant Tolerance Under Cold Conditions in Two Generations. 
     In this study, the seedling area of transgenic plants within a seed line was compared to that of non-transgenic segregants within the same seed line after 18 days of growth at 8° C., except where indicated. Five T 2  events of ME09090 were analyzed as described in the Cold Growth Assay. Two Events, −03 and −04, were significant in both generations at p≦0.05 using a one-tailed t-test assuming unequal variance. T 3  generation seedlings for Events −03 and −04 were also significant at p≦0.05 (Tables 5-1 and 5-2). The transgenic plants were visibly larger than the controls. 
     When the analysis of the T 2  generation of Event −03 was repeated with the T 3  generation, it was only significant at p≦0.17. This slight reduction in significance is most likely due to experimental variation (Table 4-1). This analysis was repeated and the T 2  generation of Event −03 was significant at p≦0.05 (Table 4-2). 
     The preferred control for analysis is the non-transgenic segregants within a seed line. However, since two of the T 3  generation seed lines of Event −03 did not segregate any non-transgenic seedlings, comparisons were made to pooled non-transgenic segregants from all Events and generations of ME09090 in the experiment. For both seed lines, the transgenic seedlings were significantly larger than the pooled non-transgenic segregants. 
     
       
         
           
               
             
               
                 TABLE 4-1 
               
             
            
               
                   
               
               
                 T-test comparison of seedling area between transgenic seedlings and control 
               
               
                 non-transgenic segregants after 18 days at 8° C. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 Control Non- 
                   
               
               
                   
                 Event- 
                 Transgenic 
                 Transgenics b   
                 t-test 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Events 
                 Gen 
                 Avg 
                 SE 
                 N 
                 Avg 
                 SE 
                 N 
                 p-value 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 ME09090-03 a   
                 03-T2 
                 0.0947 
                 0.0031 
                 19 
                 0.0775 
                 0.0025 
                 10 
                 0.0001 
               
               
                 ME09090-03 
                 03-T2 
                 0.2024 
                 0.0058 
                 48 
                 0.1922 
                 0.0086 
                 11 
                 0.1666 
               
               
                 ME09090-03-01 c   
                 03-T3 
                 0.2230 
                 0.0099 
                 57 
                 0.1860 
                 0.0046 
                 107 
                 0.0004 
               
               
                 ME09090-03-02 
                 03-T3 
                 0.1812 
                 0.0100 
                 39 
                 0.1522 
                 0.0115 
                 19 
                 0.0307 
               
               
                 ME09090-03-04 c   
                 03-T3 
                 0.2058 
                 0.0078 
                 56 
                 0.1860 
                 0.0046 
                 107 
                 0.0153 
               
               
                 ME09090-04 a   
                 04-T2 
                 0.0895 
                 0.0038 
                 26 
                 0.0757 
                 0.0014 
                 4 
                 0.0009 
               
               
                 ME09090-04 
                 04-T2 
                 0.2291 
                 0.0078 
                 45 
                 0.1986 
                 0.0067 
                 15 
                 0.0023 
               
               
                 ME09090-04-02 
                 04-T3 
                 0.2182 
                 0.0082 
                 41 
                 0.1865 
                 0.0123 
                 19 
                 0.0178 
               
               
                 ME09090-04-04 
                 04-T3 
                 0.2270 
                 0.0059 
                 47 
                 0.1908 
                 0.0165 
                 13 
                 0.0218 
               
               
                   
               
               
                   a These events were sown twice. 
               
               
                   b Transgenic seedlings were compared to non-transgenic segregants within a seed line unless otherwise indicated. 
               
               
                   c These events were compared to pooled non-transgenics for the line. 
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4-2 
               
             
            
               
                   
               
               
                 T-test comparison of seedling area between transgenic seedlings and control 
               
               
                 non-transgenic segregants after 18 days at 8° C. 
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                   
                 Control Non- 
                   
               
               
                   
                 Event- 
                 Transgenic 
                 Transgenics a   
                 t-test 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Events 
                 Gen 
                 Avg 
                 SE 
                 N 
                 Avg 
                 SE 
                 N 
                 p-value 
               
               
                   
               
               
                 ME09090-03 
                 03-T2 
                 0.0990 
                 0.0034 
                 42 
                 0.0716 
                 0.0044 
                 17 
                 4.03E−06 
               
               
                 ME09090-03-02 
                 03-T3 
                 0.0829 
                 0.0033 
                 42 
                 0.0680 
                 0.0023 
                 18 
                 2.68E−04 
               
               
                 ME09090-04 
                 04-T2 
                 0.1018 
                 0.0034 
                 38 
                 0.0751 
                 0.0024 
                 18 
                 1.42E−08 
               
               
                 ME09090-04-01 
                 04-T3 
                 0.0907 
                 0.0042 
                 42 
                 0.0759 
                 0.0029 
                 18 
                 2.71E−03 
               
               
                 ME09090-04-02 
                 04-T3 
                 0.0872 
                 0.0029 
                 45 
                 0.0713 
                 0.0053 
                 15 
                 5.33E−03 
               
               
                 ME09090-04-04 
                 04-T3 
                 0.0941 
                 0.0034 
                 45 
                 0.0696 
                 0.0049 
                 14 
                 6.14E−05 
               
               
                   
               
               
                   a Transgenic seedlings were compared to non-transgenic segregants within a seed line. 
               
            
           
         
       
     
     Example 5 
     Determination of Functional Homologs by Reciprocal BLAST 
     A candidate sequence was considered a functional homolog of a reference sequence if the candidate and reference sequences encoded proteins having a similar function and/or activity. A process known as Reciprocal BLAST (Rivera et al., Proc. Natl. Acad. Sci. USA, 95:6239-6244 (1998)) was used to identify potential functional homolog sequences from databases consisting of all available public and proprietary peptide sequences, including NR from NCBI and peptide translations from Ceres clones. 
     Before starting a Reciprocal BLAST process, a specific reference polypeptide was searched against all peptides from its source species using BLAST in order to identify polypeptides having BLAST sequence identity of 80% or greater to the reference polypeptide and an alignment length of 85% or greater along the shorter sequence in the alignment. The reference polypeptide and any of the aforementioned identified polypeptides were designated as a cluster. 
     The BLASTP version 2.0 program from Washington University at Saint Louis, Mo., USA was used to determine BLAST sequence identity and E-value. The BLASTP version 2.0 program includes the following parameters: 1) an E-value cutoff of 1.0e-5; 2) a word size of 5; and 3) the -postsw option. The BLAST sequence identity was calculated based on the alignment of the first BLAST HSP (High-scoring Segment Pairs) of the identified potential functional homolog sequence with a specific reference polypeptide. The number of identically matched residues in the BLAST HSP alignment was divided by the HSP length, and then multiplied by 100 to get the BLAST sequence identity. The HSP length typically included gaps in the alignment, but in some cases gaps were excluded. 
     The main Reciprocal BLAST process consists of two rounds of BLAST searches; forward search and reverse search. In the forward search step, a reference polypeptide sequence, “polypeptide A,” from source species SA was BLASTed against all protein sequences from a species of interest. Top hits were determined using an E-value cutoff of 10 −5  and a sequence identity cutoff of 35%. Among the top hits, the sequence having the lowest E-value was designated as the best hit, and considered a potential functional homolog or ortholog. Any other top hit that had a sequence identity of 80% or greater to the best hit or to the original reference polypeptide was considered a potential functional homolog or ortholog as well. This process was repeated for all species of interest. 
     In the reverse search round, the top hits identified in the forward search from all species were BLASTed against all protein sequences from the source species SA. A top hit from the forward search that returned a polypeptide from the aforementioned cluster as its best hit was also considered as a potential functional homolog. 
     Functional homologs were identified by manual inspection of potential functional homolog sequences. Representative functional homologs for SEQ ID NOs: 80, 99, 128, 134, 144, 151, 159, 163, 168, 173, 177, 191, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, 259, and 119 are shown in  FIGS. 1-2 , and in the Sequence Listing of this application. 
     Example 6 
     Determination of Functional Homologs by Hidden Markov Models 
     Hidden Markov Models (HMMs) were generated by the program HMMER 2.3.2. To generate each HMM, the default HMMER 2.3.2 program parameters, configured for glocal alignments, were used. 
     An HMM was generated using the sequences shown in  FIG. 1  as input. These sequences were fitted to the model and a representative HMM bit score for each sequence is shown in the Sequence Listing. Additional sequences were fitted to the model, and representative HMM bit scores for any such additional sequences are shown in the Sequence Listing. The results indicate that these additional sequences are functional homologs of SEQ ID NOs: 80, 99, 128, 134, 144, 151, 159, 163, 168, 173, 177, 191, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258, and 259. 
     The procedure above was repeated and an HMM was generated for the group of sequences shown in  FIG. 2 , using the sequences shown in  FIG. 2  as input for that HMM. A representative bit score for each sequence is shown in the Sequence Listing. Additional sequences were fitted to certain HMMs, and representative HMM bit scores for such additional sequences are shown in the Sequence Listing. The results indicate that these additional sequences are functional homologs of the sequences used to generate that HMM. 
     Other Embodiments 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.