Different Cold-Signaling Pathways Function in the Responses to Rapid and Gradual Decreases in Temperature.

In plants, cold temperatures trigger stress responses and long-term responses that result in cold tolerance. In , three dehydration-responsive element (DRE) binding protein 1/C-repeat binding factors (DREB1/CBFs) act as master switches in cold-responsive gene expression. Induction of genes triggers the cold stress-inducible transcriptional cascade, followed by the induction of numerous genes that function in the cold stress response and cold tolerance. Many regulatory factors involved in induction have been identified, but how these factors orchestrate the cold stress-specific expression of has not yet been clarified. Here, we revealed that plants recognize cold stress as two different signals, rapid and gradual temperature decreases, and induce expression of the genes. CALMODULIN BINDING TRANSCRIPTION ACTIVATOR3 (CAMTA3) and CAMTA5 respond to a rapid decrease in temperature and induce the expression of , but these proteins do not respond to a gradual decrease in temperature. Moreover, they function during the day and night, in contrast to some key circadian components, including CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL, which regulate cold-responsive expression as transcriptional activators only during the day. Thus, plants efficiently control the acquisition of freezing tolerance using two different signaling pathways in response to a gradual temperature decrease during seasonal changes and a sudden temperature drop during the night.