Lighting-up Wars: Stories of Ca2+ Signaling in Plant Immunity

Calcium ions (Ca²⁺) serve as key messengers in plant immune reactions. A typical Ca²⁺ signaling involves three steps: encoding specific Ca²⁺ signatures by Ca²⁺-permeable channels, decoding Ca²⁺ signals by Ca²⁺ sensors, and downstream responses. This review focuses on plasma membrane-localized Ca²⁺-permeable channels and cytosolic Ca²⁺ sensors, unraveling their roles in cytosolic Ca²⁺ influx and immune signaling during pattern-triggered immunity, effector-triggered immunity, and autoimmunity. Several unresolved questions were highlighted, including the regulation of Ca²⁺-permeable channel activity for immune induction and the mechanism behind Ca²⁺ influx-triggered hypersensitive response cell death. This concise overview provides insights into the complex interplay of Ca²⁺ signaling in plant immunity, paving the way for future investigations on molecular plant-microbe interactions.