Cytoplasmic Ca Influx Mediates Iron- and Reactive Oxygen Species-dependent Ferroptotic Cell Death in Rice Immunity

Iron- and reactive oxygen species (ROS)-dependent ferroptosis occurs in plant cells. Ca acts as a conserved key mediator to control plant immune responses. Here, we report a novel role of cytoplasmic Ca influx regulating ferroptotic cell death in rice immunity using pharmacological approaches. High Ca influx triggered iron-dependent ROS accumulation, lipid peroxidation, and subsequent hypersensitive response (HR) cell death in rice (). During infection, 14 different Ca influx regulators altered Ca, ROS and Fe accumulation, () expression, glutathione (GSH) depletion and lipid peroxidation, leading to ferroptotic cell death in rice. High Ca levels inhibited the reduction of glutathione isulphide (GSSG) to GSH . Ca chelation by ethylene glycol-bis (2-aminoethylether)--tetra-acetic acid (EGTA) suppressed apoplastic Ca influx in rice leaf sheaths during infection. Blocking apoplastic Ca influx into the cytoplasm by Ca chelation effectively suppressed Ca-mediated iron-dependent ROS accumulation and ferroptotic cell death. By contrast, acibenzolar--methyl (ASM), a plant defense activator, significantly enhanced Ca influx, as well as ROS and iron accumulation to trigger ferroptotic cell death in rice. The cytoplasmic Ca influx through calcium-permeable cation channels, including the putative resistosomes, could mediate iron- and ROS-dependent ferroptotic cell death under reduced expression levels in rice immune responses.