OsCPK12-OsATPD1 Module Regulates Photosynthetic Acclimation to Light Stress in Rice.

The synergy between light and dark reactions is the key to photosynthesis. This synergy not only helps plants achieve maximum photosynthetic efficiency but also plays a crucial role in photosynthetic protection. However, the mechanisms through which plants regulate this process remain unclear. In this study, we demonstrated that the calcium-dependent protein kinase OsCPK12 is essential for mediating rice's responses to light intensity. The oscpk12-cr mutant displayed light-sensitive premature senescence. Specifically, light-induced OsCPK12 expression targeted Ser8 on the chloroplast transit peptide of OsAtpD1, a subunit of ATP synthase, thereby promoting its transport into chloroplasts. OsAtpD1S8D overexpression in oscpk12-cr rescued its premature senescence. ATPase activity and electron transport rate (ETR) were decreased in oscpk12-cr, oscpk12-cr/OE-OsAtpD1S8A, and RNAi-OsAtpD1 plants. In contrast, OsCPK12 overexpression in rice resulted in higher ATPase activity and ETR than in ZH8015. Overall, OsCPK12 phosphorylated OsAtpD1 to promote its chloroplast translocation, thereby maintaining ATP synthase activity and proton gradient (ΔpH) homeostasis and regulating photosynthetic acclimation, photoprotection, and repair under light stress. Our findings reveal the intrinsic mechanism by which the OsCPK12-OsATPD1 module regulates ATP synthase activity and ETR efficiency, fine-tuning photosynthetic acclimation to prevent light damage.