Natural variations in the OsCPK9 promoter confer chilling tolerance in rice by stabilizing OsSAPK8 through...

The response and integration of cold signals are key processes when plants cope with cold stress. It remains a challenging problem to study the function of calcium (Ca²⁺) sensor in mediating the Ca²⁺ signaling during the early stage of cold signal transduction.

Here, we focused on the Ca²⁺ sensor gene OsCPK9 to explore its function in chilling tolerance. Our results showed that OsCPK9 exhibits a significant cold-induced expression pattern, and contributes to chilling tolerance at seedling stages. The haplotype and population genetics analysis indicated that the promoter region of OsCPK9 harbors favorable allelic variations that were strongly selected during the domestication process of japonica rice. Furthermore, OsCPK9 interact with five members of the OsSAPK family whose C-terminal domain is the determining factor. Upon exposure to chilling, OsCPK9 phosphorylates OsSAPK8 at Ser178 and Ser187, and stabilizes OsSAPK8 in a Ca²⁺-dependent manner, thereby activating the downstream responses.

Our findings demonstrated that the OsCPK9-OsSAPK8 module regulates chilling tolerance through Ca²⁺-mediated phosphorylation during the early stages of cold signal transduction. Furthermore, the elite allelic variation of OsCPK9 is an excellent candidate site for precise editing to enhance rice's tolerance to chilling stress.