Integration of Ca²⁺ in plant drought and salt stress signal transduction pathways

Plants cope with environmental changes by activating signal transduction cascades that control and coordinate the physiological and biochemical responses necessary for adaptation. Numerous signaling pathways that function as an integrated network have been implicated in plant abiotic stress response. Amongst them, calcium signaling was found to be incorporated in different signaling pathways during abiotic stress response, e.g. to heat, cold, drought, and salt. A well-recognized model of calcium signaling is that calcium signals characteristic of either elevation or oscillation of cytosolic Ca²⁺ is generated upon stimulation and then transduced through an array of Ca ²⁺ activated proteins and downstream components, including calmodulins (CaMs) and CaM-binding proteins (CaMBPs), calcineurin B-like proteins (CBLs), Ca²⁺-dependent protein kinases (CDPKs), Ca ²⁺ and CaM-binding transcription factors, and other Ca ²⁺-binding proteins. Potential targeted effectors of calcium signaling include important enzymes/proteins involved in various cellular metabolism and physiological adjustment. This review begins with the generation of calcium signals followed by reviewing components decoding calcium signals. Implication of the signaling components in drought and salt stress response is emphasized and discussed