Mechanism of in regulating cold tolerance of cucumber.

G proteins function directly in cold tolerance of plants. However, the framework of the Gα subunit in regulating cold tolerance remains to be explored. Here, we used protein interaction techniques to elucidate cold-related pathways regulated by CsGPA1. Suppression of decreased the cold tolerance of cucumber. Further protein interaction experiments showed that CsGPA1 interacted with Csa_4G663630.1 located in the cell membrane and nucleus and with CsCOR413PM2 located in the cell membrane. Csa_4G663630.1 was named CsCDL1 due to its 71% protein sequence similarity to AtCDL1, a positive brassinolide signal gene. Suppression of decreased the expression of most of brassinolide-related genes (including ) under cold stress. Principal component and linear regression analyses showed that expressions of and brassinolide-related genes were positively correlated. Suppression of also decreased cold tolerance of cucumber. The expression and protein content of and in -RNAi and -RNAi lines were determined under cold tolerance. Only silencing affected the expression and protein content of during cold stress. Moreover, suppression of or decreased Ca influx at low temperature and then decreased the expression of -. These results indicated that the --Ca axis regulated the expression of - during cold stress. In conclusion, Our results provide the first framework of in regulating cold tolerance of cucumber, laying the foundation for further mechanistic studies of cold tolerance for Gα in cucumber.