OsCPK12 phosphorylates OsCATA and OsCATC to regulate H₂O₂ homeostasis and improve oxidative stress tolerance in rice

Calcium-dependent protein kinases (CPKs), the best-characterized calcium sensors in plants, regulate many aspects of plant growth and development as well as plant adaptation to biotic and abiotic stresses. However, how CPKs regulate the antioxidant defense system remains largely unknown. We previously found that impaired function of OsCPK12 leads to oxidative stress in rice, with more H₂O₂, lower catalase (CAT) activity, and lower yield. Here, we explored the roles of OsCPK12 in oxidative stress tolerance in rice. Our results show that OsCPK12 interacts with and phosphorylates OsCATA and OsCATC at Ser11. Knockout of either OsCATA or OsCATC leads to an oxidative stress phenotype accompanied by higher accumulation of H₂O₂. Overexpression of the phosphomimetic proteins OsCATA^S11D and OsCATC^S11D in oscpk12-cr reduced the level of H₂O₂ accumulation. Moreover, OsCATA^S11D and OsCATC^S11D showed enhanced catalase activity in vivo and in vitro. OsCPK12-overexpressing plants exhibited higher CAT activity as well as higher tolerance to oxidative stress. Our findings demonstrate that OsCPK12 affects CAT enzyme activity by phosphorylating OsCATA and OsCATC at Ser11 to regulate H₂O₂ homeostasis, thereby mediating oxidative stress tolerance in rice.