Calcium signaling network in abiotic stress tolerance in plants

Abstract Unlike humans, plants do not have the ability to move, thus, they have a plethora of tolerance mechanisms that help them to survive under various environmental stresses. This ability to quickly sense stress and activate the appropriate stress response mechanism is essential to the abiotic stress tolerance of a plant. The functional role of Ca2+ is very well known in signaling the emergence of stress and then eliciting the activation of an appropriate tolerance mechanism. The concentration of free cytosolic Ca2+ [Ca2+] cyt transiently increases in response to various abiotic stresses such as cold, drought, and high salinity. These Ca2+ transients, known as Ca2+ signatures, rely on the counter activities of Ca2+ transporting proteins and Ca2+ permeable channels. Active transport of Ca2+ from the cytosol into the apoplast or to the intracellular organelles is an energy-driven process and takes place against the electrochemical gradient. The key proteins involved in this movement are Ca2+ ATPases and H+/Ca2+ antiporters. The increase in the concentration of Ca2+ is sensed by some calcium-binding proteins (CBPs) or sensor proteins, which lead to the activation of different calcium-dependent protein kinases. These kinases play an important role in regulating the function of a myriad of genes including stress-responsive genes, resulting in stress tolerance. Gene expression regulation by cellular calcium is also essential for imparting stress tolerance to plants. Hence, a better understanding of the function of these genes would help in elucidating the Ca2+-mediated signaling network and its function in plant growth, development, and response toward various abiotic stresses.