Differential and coordinated expression of Cbf and Cor/Lea genes during long-term cold acclimation in two wheat cultivars showing distinct levels of freezing tolerance.

The cold acclimation process in plants is primarily regulated through the signal transduction pathways that lead to the induction and enhancement of expression of different sets of Cor/Lea genes. Winter wheat 'Mironovskaya 808' (M808) exhibited a much higher level of freezing tolerance than spring wheat 'Chinese Spring' (CS), and the difference became clearer after the long-term cold acclimation. To understand the molecular basis of this cultivar difference, we isolated two CBF/DREB1 homologs, Wcbf2, which are the candidate gene for a transcription factor of the Cor/Lea genes. Expression of the Wcbf2 gene was induced rapidly by low temperature (LT) and drought but not by abscisic acid (ABA). The gene expression was temporal and at least twice up-regulated by LT. The first up-regulation occurred within 1-4 h, which might correspond to the rapid response to LT, while the second up-regulation occurred during 2-3 weeks of cold acclimation. After the second up-regulation, the amount of Wcbf2 transcript greatly decreased in CS, while it increased again in M808 after 4 weeks until 9 weeks (end of the test period). The maintenance of this high level of the Wcbf2 transcript might represent the long-term effect of cold acclimation. The activation of Cor/Lea genes followed the accumulation of Wcbf2 transcript suggested direct involvement of the Wcbf2 gene in the induction and enhancement of the Cor/Lea gene expression. The cultivar difference in freezing tolerance developed during different stages of cold acclimation can be at least partly explained by the differential and coordinated regulation of the predicted Cor/Lea gene signal transduction pathway that is mediated by the CBF/DREB1 transcription factors in common wheat.