Mitogen-Activated Protein Kinase Kinase OsMEK2 Positively Regulates Ca²⁺ Influx and Ferroptotic Cell Death during...

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 Ca²⁺. High Ca²⁺ influx triggered iron-dependent ROS accumulation, lipid peroxidation, and subsequent hypersensitive response (HR) cell death in rice (Oryza sativa). Apoplastic Ca²⁺ chelation by EGTA during avirulent Magnaporthe oryzae infection altered Ca²⁺, ROS, and Fe²⁺ accumulation, increasing rice susceptibility to infection. By contrast, acibenzolar-S-methyl (ASM), a plant defense activator, significantly enhanced Ca²⁺ influx, and H₂O₂ 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 Ca²⁺ 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 Ca²⁺ regulation in rice ferroptotic cell death, suggesting its broader role in plant immune responses in response to M. oryzae infection.