Isolation of a cDNA clone and characterization of expression of the highly abundant, cold acclimation-associated 14Â kDa dehydrin of blueberry

Dehydrins are a family of plant proteins that are induced by dehydrative stresses such as those caused by drought, salinity, and low/freezing temperature. Induction of some dehydrins may be responsive to ABA and/or short photoperiod as well. Previously, we reported that in blueberry a family of dehydrins of 65, 60, and 14 kDa accumulates in floral buds during the winter, and the levels of these proteins correlate with cold tolerance. Decline in level of the 14 kDa dehydrin with exposure to warm temperatures correlates well with loss of hardiness or deacclimation also. In the present study, we identified and sequenced a cDNA clone from blueberry floral bud RNA that encodes the 14 kDa dehydrin. The identity of the clone was confirmed by comparing partial peptide sequences from the protein with deduced protein sequence from the cDNA. The cDNA was found to be a full-length 653 bp clone, comprised of a 55 bp 5′ UTR, an ORF of 303 bp, a 213 bp 3′ UTR, and an 82 bp polyA tail. The cDNA has 2 K boxes, indicative of dehydrins, and no Y or S segments; thus it was classified as a K2 type dehydrin. Expression of the 14 kDa dehydrin was studied at the transcript and protein levels in stem and leaf tissues under induced cold and drought stress in two genotypes, 'Bluecrop' and 'Premier', which differ in terms of their cold and drought tolerances. Expression of the protein was monitored using a polyclonal antibody raised against a synthetic peptide of the consensus K box of blueberry dehydrins, which was found to cross react with many blueberry dehydrins. The 14 kDa dehydrin, like other Kn type dehydrins, was strongly induced by cold stress and to a lesser extent by drought stress. A previously uncharacterized 16 kDa dehydrin showed similar induction on Western blots; however, it appeared to increase over time during the course of the experiments in stems of the southern variety 'Premier'. Like some other dehydrins and bark storage proteins, expression of the 16 kDa dehydrin may be responsive to short photoperiods. Patterns of expression of the 14 kDa dehydrin at the protein level were very consistent with patterns at the RNA level, and the 14 kDa dehydrin message was induced to higher levels in the more cold hardy and drought tolerant genotype, 'Bluecrop', than in 'Premier'.