Calcium signatures and signaling events orchestrate plant-microbe interactions.

Calcium (Ca) acts as an essential second messenger connecting the perception of microbe signals to the establishment of appropriate immune and symbiotic responses in plants. Accumulating evidence suggests that plants distinguish different microorganisms through plasma membrane-localized pattern recognition receptors. The particular recognition events are encoded into Ca signatures, which are sensed by diverse intracellular Ca binding proteins. The Ca signatures are eventually decoded to distinct downstream responses through transcriptional reprogramming of the defense or symbiosis-related genes. Recent observations further reveal that Ca-mediated signaling is also involved in negative regulation of plant immunity. This review is intended as an overview of Ca signaling during immunity and symbiosis, including Ca responses in the nucleus and cytosol.