Abstract: Calcium ions (Ca²⁺) are crucial intracellular second messengers in eukaryotic cells. Upon pathogen perception, plants generate a transient and rapid increase in cytoplasmic Ca²⁺ levels, which is subsequently decoded by Ca²⁺ sensors and effectors to activate downstream immune responses. The elevation of cytosolic Ca²⁺ is commonly attributed to Ca²⁺ influx mediated by plasma membrane-localized Ca²⁺–permeable channels. However, the contribution of Ca²⁺ release triggered by intracellular Ca²⁺-permeable channels in shaping Ca²⁺ signaling associated with plant immunity remains poorly understood. This review discusses recent advances in understanding the mechanism underlying the shaping of Ca²⁺ signatures upon the activation of immune receptors, with particular emphasis on the identification of intracellular immune receptors as non-canonical Ca²⁺-permeable channels. We also discuss the involvement of Ca²⁺ release from the endoplasmic reticulum in generating Ca²⁺ signaling during plant immunity.

Key words: Ca²⁺-permeable channels, endoplasmic reticulum, phosphorylation, plant immunity, resistosome