CbCOR15, A Cold-Regulated Gene from Alpine Chorispora bungeana, Confers Cold Tolerance in Transgenic Tobacco

Rapid amplification of cDNA ends was performed to isolate cold-regulated CbCOR15 (EF208112) from Chorispora bungeana. This alpine species is distributed in subnival areas. Transcripts were detected in the leaves, but not the roots, of plants acclimated to cold temperatures. Expression was induced at high levels at both 4A degrees C and -4A degrees C. In comparing its deduced protein sequence to that of AtCOR15a (cold-regulated 15a in Arabidopsis thaliana), the N terminus had less homology than the C terminus while still containing a region analogous to the chloroplast-targeted signal peptide of AtCOR15a. We also introduced CbCOR15, with the CaMV 35S promoter, into tobacco. Second-generation (T1) plants had significantly increased tolerance to chilling, as determined by their electrolyte leakage, chlorophyll content, and relative water content. Further freezing-stress experiments showed that the tolerance of transgenic lines was significantly greater than that of the nontransgenics. Although the degree of chilling and freezing tolerance in the transgenic plants was not directly correlated with the accumulated levels of CbCOR15, we could conclude that this gene confers cold tolerance.