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.