Chilling-induced phosphorylation of IPA1 by OsSAPK6 activates chilling tolerance responses in rice

Chilling is a major abiotic stress harming rice development and productivity. The C-REPEAT BINDING FACTOR (CBF)-dependent transcriptional regulatory pathway plays a central role in cold stress and acclimation in Arabidopsis. In rice, several genes have been reported in conferring chilling tolerance, however, the chilling signaling in rice remains largely unknown. Here, we report the chilling-induced OSMOTIC STRESS/ABA-ACTIVATED PROTEIN KINASE 6 (OsSAPK6)-IDEAL PLANT ARCHITECTURE 1 (IPA1)-OsCBF3 signal pathway in rice. Under chilling stress, OsSAPK6 could phosphorylate IPA1 and increase its stability. In turn, IPA1 could directly bind to the GTAC motif on the OsCBF3 promoter to elevate its expression. Genetic evidence showed that OsSAPK6, IPA1 and OsCBF3 were all positive regulators of rice chilling tolerance. The function of OsSAPK6 in chilling tolerance depended on IPA1, and overexpression of OsCBF3 could rescue the chilling-sensitive phenotype of ipa1 loss-of-function mutant. Moreover, the natural gain-of-function allele ipa1-2D could simultaneously enhance seedling chilling tolerance and increase grain yield. Taken together, our results revealed a chilling-induced OsSAPK6-IPA1-OsCBF signal cascade in rice, which shed new lights on chilling stress-tolerant rice breeding.