シロイヌナズナにおけるCAMTA 転写因子による低温誘導性遺伝子の発現制御

抄録

In Arabidopsis, three transcription factors DRE-binding protein 1/C-repeat binding factors (DREB1/CBFs) function as master switches in cold stress-inducible gene expression. Because the expression of the DREB1 genes is rapidly induced in the cold stress responses, this induction seems to be the first step for the cold stressinducible transcriptional cascade followed by the expression of numerous genes that function in the cold stress response. We have revealed that the 65-bp fragment of the DREB1C promoter contains positive regulatory elements for the cold-inducible expression. By using yeast one-hybrid screens, one of Calmodulin-binding transcription activator (CAMTA) family proteins was identified as a positive regulatory factor that interacts with this fragment. The analyses using the multiple mutants of the CAMTA genes revealed that plants recognize cold stress as two different signaling pathways for inducing the expression of the DREB1 genes under cold stress conditions. In one pathway, CAMTA3 and CAMTA5 activate the expression of DREB1B and DREB1C by a rapid temperature decrease. In another one, the circadian clock components including CCA1/LHY induce the expression of DREB1A and DREB1C only in the daytime independent to the cooling rate. These two signaling pathways enable plants to efficiently acquire cold acclimation capacity or freezing tolerance.