Mitogen-Activated Protein Kinase Kinase OsMEK2 Positively Regulates Ca 2+ Influx and Ferroptotic Cell Death during Rice Immune Responses.

Mitogen-activated protein (MAP) kinase (MAPK) signaling pathway is important in plant immune responses, involved in iron- and reactive oxygen species (ROS)-dependent ferroptotic cell death mediated by Ca 2+ . High Ca 2+ influx triggered iron-dependent ROS accumulation, lipid peroxidation, and subsequent hypersensitive response (HR) cell death in rice ( Oryza sativa ). Apoplastic Ca 2+ chelation by EGTA during avirulent Magnaporthe oryzae infection altered Ca 2+ , ROS, and Fe 2+ accumulation, increasing rice susceptibility to infection. By contrast, acibenzolar- S -methyl (ASM), a plant defense activator, significantly enhanced Ca 2+ influx, and H 2 O 2 accumulation, triggering rice ferroptotic cell death during virulent Magnaporthe oryzae infection. Here, we report a novel role of the MAPK signaling pathway in regulating cytoplasmic Ca 2+ increase during ferroptotic cell death in rice immunity, using the ΔOsmek2 knockout mutant rice. The knockout of rice OsMEK2 impaired the ROS accumulation, lipid peroxidation, and iron accumulation during avirulent M. oryzae infection. This study has shown that OsMEK2 could positively regulate iron- and ROS-dependent ferroptotic cell death in rice by modulating the expression of OsNADP-ME , OsRBOHB , OsPLC , and OsCNGC . This modulation indicates a possible mechanism for how OsMEK2 participates in Ca 2+ regulation in rice ferroptotic cell death, suggesting its broader role in plant immune responses in response to M. oryzae infection.