Low temperature combined with lack of cold hardiness are among the major causes of plant yield reduction and losses in commerce and the most limiting factor to natural plant distribution (Parker, 1963). Winter injury is one of the most important factors limiting growth of woody perennials in North America (Quamme, 1985). Periodic winter freezes result in serious losses in fruit, nut, and ornamental crops. Consequently, a major emphasis of many breeding programs on woody plants is the development of more cold-hardy cultivars.
To survive the winter, woody perennials of the temperate zone increase their freezing tolerance seasonally by a process known as cold acclimation. Cold acclimation in woody perennials is generally considered a two-step process, first triggered by shortening daylength and then declining temperatures, subsequently into the subfreezing range (Powell, 1987; Sakai and Larcher, 1987; Weiser, 1970). Herbaceous plants, on the other hand, acclimate to maximum cold-hardiness levels by exposure to low, nonfreezing temperatures, and their cold acclimation capacity is generally less than that of woody species (Kacperska-Palacz, 1978). Thus, cold acclimation is considered more complex in woody perennials; woody plants that would be killed by temperatures slightly below 0 °C during summer may survive temperatures as low as −196 °C during winter (Sutinen et al., 1992).
Genetic evidence from both herbaceous and woody plants indicates that cold hardiness is controlled by several genes; thus, it is a quantitative trait (Arora et al., 2000; Byrne et al., 1997; Howe et al., 2000; Jermstad et al., 2001). Considerable molecular and genomic evidence indicates that cold acclimation is a complex phenomenon involving changes in expression of many genes resulting in the alteration of metabolism and composition of cell walls, lipids, proteins, and carbohydrates (Fowler and Thomashow, 2002; Guy, 1990, 1999; Seki et al., 2001; Shinozaki and Yamaguchi-Shinozaki, 1996, 2000; Thomashow, 1999, 2001). Within the last few years, microarrays have been used in Arabidopsis to study changes in gene expression on a large scale during cold stress. Fowler and Thomashow (2002) used commercially available microarrays to examine transcript levels of ≈8000 genes in cold-stressed Arabidopsis plants; 306 of these genes were cold-responsive, 218 being upregulated and 88 being downregulated. More than one-fourth of the cold-responsive genes did not appear to be regulated by C-repeat binding factor or CBF proteins (transcription factors responsible for the upregulation of many genes in response to cold and drought stress), indicating that multiple regulatory pathways are activated during cold acclimation. Maruyama et al. (2004) identified new members of the CBF regulon using microarrays and transgenic plants overexpressing CBFs. A recent article by Hannah et al. (2005) summarizes the microarray data on cold stress in Arabidopsis.
Over the past several years, we have studied the biology of cold tolerance in blueberry with an ultimate goal of applying the information to develop more cold-hardy cultivars. For blueberry, lack of winter freezing tolerance and susceptibility to spring frosts have been identified as the most important genetic limitations of current cultivars (Moore, 1993). Working with a woody perennial, however, the focus of our studies has been different from those in Arabidopsis. For example, our studies have focused on natural, seasonal cold acclimation. We have also focused on flower bud tissue, rather than leaf tissue, because damage to flower buds directly results in reduction in fruit yield. In addition, we have examined changes in gene expression over a longer period of time, throughout the duration of winter. Blueberry reaches maximum freezing tolerance midwinter and some genotypes can acclimate to ≈−25 to −30 °C. See Table 1 for a list of cultivars and their levels of flower bud cold hardiness during midwinter. In contrast, Arabidopsis reaches maximum cold tolerance relatively quickly but only cold acclimates ≈5 to 7 °C allowing for brief exposures to freezing temperatures. Furthermore, we have tried to interpret our findings keeping in mind that overwintering flower buds exhibit both enhanced freezing tolerance and dormancy transitions.
Maximum flower bud cold-hardiness levels and germplasm composition of field-grown blueberry plants of eight cultivars using a freeze–thaw protocol described previouslyz.
Alkharouf, N.W., Dhanaraj, A.L., Naik, D., Overall, C., Matthews, B.F. & Rowland, L.J. 2007 BBGD: An online database for blueberry genomic data Biomed Central Plant Biology 7 5
Altschul, S.F., Madden, T.L., Schaffer, A.A., Zhang, J., Zhang, A., Miller, W. & Lipmann, D.J. 1997 Gapped BLAST and PSI-BLAST: A new generation of protein database search programs Nucleic Acids Res. 25 3389 3402
Arora, R., Rowland, L.J., Lehman, J.S., Lim, C.C., Panta, G.R. & Vorsa, N. 2000 Genetic analysis of freezing tolerance in blueberry (Vaccinium section Cyanococcus) Theor. Appl. Genet. 100 690 696
Arora, R., Rowland, L.J. & Panta, G.R. 1997 Chill responsive dehydrins in blueberry: Are they associated with cold hardiness or dormancy transitions? Physiol. Plant. 101 8 16
Byrne, M., Murrell, J.C., Owen, J.V., Williams, E.R. & Moran, G.F. 1997 Mapping of quantitative trait loci influencing frost tolerance in Eucalyptus nitens Theor. Appl. Genet. 95 975 979
Dhanaraj, A.L., Alkharouf, N.W., Beard, H.S., Chouikha, I.B., Matthews, B.F., Wei, H., Arora, R. & Rowland, L.J. 2007 Major differences observed in transcript profiles of blueberry during cold acclimation under field and cold room conditions Planta 225 735 751
Dhanaraj, A.L., Slovin, J.P. & Rowland, L.J. 2004 Analysis of gene expression associated with cold acclimation in blueberry floral buds using expressed sequence tags Plant Sci. 166 863 872
Dhanaraj, A.L., Slovin, J.P. & Rowland, L.J. 2005 Isolation of a cDNA clone and characterization of expression of the highly abundant, cold acclimation-associated 14 kDa dehydrin of blueberry Plant Sci. 168 949 957
Ezhova, T.A., Soldatova, O.P., Kalinina, A.I. & Medvedev, S.S. 2000 Interaction of ABRUPTUS/PINOID and LEAFY genes during floral morphogenesis in Arabidopsis thaliana (L.) Heynh Genetika 36 1682 1687
Fowler, S. & Thomashow, M.F. 2002 Arabidopsis transcriptome profiling indicates that multiple regulatory pathways are activated during cold acclimation in addition to the CBF cold response pathway Plant Cell 14 1675 1690
Guilmour, S.J., Sebolt, A.M., Salazar, M.P., Everard, J.D. & Thomashow, M.F. 2000 Overexpression of the Arabidopsis CBF3 transcriptional activator mimics multiple biochemical changes associated with cold acclimation Plant Physiol. 124 1854 1865
Guy, C.L. 1990 Cold acclimation and freezing stress tolerance: Role of protein metabolism Ann. Rev. Plant Physiol. Plant Mol. Biol. 41 187 223
Hannah, M.A., Heyer, A.G. & Hincha, D.K. 2005 A global survey of gene regulation during cold acclimation in Arabidopsis thaliana PLoS Genetics 1 179 196
Howe, G.T., Saruul, P., Davis, J. & Chen, T.H.H. 2000 Quantitative genetics of bud phenology, frost damage, and winter survival in an F2 family of hybrid poplars Theor. Appl. Genet. 101 632 642
Jaglo-Ottosen, K.R., Guilmour, S.J., Zarka, D.G., Schabenberger, O. & Thomashow, M.F. 1998 Arabidopsis CBF1 overexpression induces COR genes and enhances freezing tolerance Science 280 104 106
Jermstad, K.D., Bassoni, D.L., Wheeler, N.C., Anekonda, T.S., Aitken, S.N., Adams, W.T. & Neale, D.B. 2001 Mapping of quantitative trait loci controlling adaptive traits in coastal Douglas-fir. II. Spring and fall cold-hardiness Theor. Appl. Genet. 102 1152 1158
Kacperska-Palacz, A. 1978 Mechanism of cold acclimation in herbaceous plants 139 152 Li P.H. & Sakai A. Plant cold hardiness and freezing stress: Mechanism and crop implications. Academic New York, NY
Kasuga, M., Liu, O., Setsuko, M., Yamaguchi-Shinozaki, K. & Shinozaki, K. 1999 Improving plant drought, salt, and freezing tolerance by gene transfer of a single stress-inducible transcription factor Nat. Biotechnol. 17 287 291
Kaye, C., Neven, L., Hofig, A., Li, Q.B., Haskell, D. & Guy, C. 1998 Characterization of a gene for spinach CAP160 and expression of two spinach cold-acclimated proteins in tobacco Plant Physiol. 116 1367 1377
Lebedeva, O.V., Ondar, U.N., Penin, A.A. & Ezhova, T.A. 2005 Effect of the ABRUPTUS/PINOID gene on expression of the LEAFY gene in Arabidopsis thaliana Genetika 41 559 565
Levi, A., Panta, G.R., Parmentier, C.M., Muthalif, M.M., Arora, R., Shanker, S. & Rowland, L.J. 1999 Complementary DNA cloning, sequencing, and expression of an unusual dehydrin from blueberry floral buds Physiol. Plant. 107 98 109
Maruyama, K., Sakuma, Y., Kasuga, M., Ito, Y., Seki, M., Goda, H., Shimada, Y., Yoshida, S., Shinozaki, K. & Yamaguchi-Shinozaki, K. 2004 Identification of cold-inducible downstream genes of the Arabidopsis DREB1A/CBF3 transcription factor using two microarray systems Plant J. 38 982 993
Muthalif, M.M. & Rowland, L.J. 1994 Identification of dehydrin-like proteins responsive to chilling in floral buds of blueberry (Vaccinium, section Cyanococcus) Plant Physiol. 104 1439 1447
Naik, D., Dhanaraj, A.L., Arora, R. & Rowland, L.J. 2007 Identification of genes associated with cold acclimation in blueberry (Vaccinium corymbosum L.) using a subtractive hybridization approach Plant Sci. 173 213 222
Owens, C.L., Thomashow, M.F., Hancock, J.F. & Iezzoni, A.F. 2002 CBF1 orthologs in sour cherry and strawberry and the heterologous expression of CBF1 in strawberry J. Amer. Soc. Hort. Sci. 127 489 494
Rowland, L.J., Mehra, S., Dhanaraj, A.L., Ogden, E.L., Slovin, J.P. & Ehlenfeldt, M.K. 2003 Development of EST-PCR markers for DNA fingerprinting and genetic relationship studies in blueberry (Vaccinium, section Cyanococcus) J. Amer. Soc. Hort. Sci. 128 682 690
Rowland, L.J., Ogden, E.L., Ehlenfeldt, M.K. & Vinyard, B. 2005 Cold hardiness, deacclimation kinetics, and bud development among 12 diverse blueberry genotypes under field conditions J. Amer. Soc. Hort. Sci. 130 508 514
Sakai, A. & Larcher, W. 1987 Frost survival of plants: Responses and adaptation to freezing stress Springer Berlin, Heidelberg, New York
Seki, M., Narusaka, M., Abe, H., Kasuga, M., Yamaguchi-Shinozaki, K., Carninci, P., Hayashizaki, Y. & Shinozaki, K. 2001 Monitoring the expression pattern of 1300 Arabidopsis genes under drought and cold stresses by using a full-length cDNA microarray Plant Cell 13 61 72
Shinozaki, K. & Yamaguchi-Shinozaki, K. 2000 Molecular responses to dehydration and low temperature: Differences and cross-talk between two stress signaling pathways Curr. Opin. Biotechnol. 3 217 223
Singh, K., Foley, R.C. & Onate-Sanchez, L. 2002 Transcription factors in plant defense and stress responses Curr. Opin. Plant Biol. 5 430 436
Sutinen, M.L., Palta, J.P. & Reich, P.B. 1992 Seasonal differences in freezing stress resistance of needles of Pinus nigra and Pinus resinosa: Evaluation of the electrolyte leakage method Tree Physiol. 11 241 254
Thomashow, M.F. 1999 Plant cold acclimation: Freezing tolerance genes and regulatory mechanisms Ann. Rev. Plant. Physiol. Plant. Mol. Biol. 50 573 599