Calcium signaling and transport machinery: Potential for development of stress tolerance in plants

Calcium (Ca2+)is an essential macronutrient as well as a second messenger in diverse biological processes in plants. Plants perceive various stimuli which leads to transient increase in cytosolic calcium [Ca2+]cyt levels, resulting in generation of Ca2+ signatures. These Ca2+ signatures are specific to various stress stimuli and developmental processes and are perceived by Ca2+ sensors. Ca2+ sensors and relay proteins participate in downstream signaling events to decode the Ca2+ signatures. Ca2+ homeostasis involves the synergistic action of transporting elements that regulate Ca2+ influx and efflux. The influx elements help elevate the [Ca2+]cyt levels during signaling events and efflux elements help in restoring the resting [Ca2+]cyt levels. These Ca2+ transporters include Cyclic nucleotide gated channels (CNGCs), Glutamate receptor-like (GLRs)channels/Glutamate-like receptor channels, Two pore channels (TPCs), Annexins, Mechanosensitive channels (MSLs), Ca2+-ATPases, Ca2+/H+ exchangers (CAXs), Ca2+/cation exchangers (CCXs). The involvement of these Ca2+ signaling and transporting elements in developmental and physiological processes as well as responses to diverse stress factors accounts for their significance. In this review, we highlight the progress of genomic approaches in dissecting the role of Ca2+ signaling components in mediating stress tolerance in plants, in the context of changing climatic conditions.