Unraveling the importance of EF-hand mediated calcium signaling in plants

Calcium (Ca2+) is an essential element for the growth and development and provides rigidity to plant cells in calcium pectate form, and also involved in microtubule formation, cell proliferation, and stress tolerance. Ca2+ is a ubiquitous intracellular secondary messenger regulating the signal transduction pathway through signals encoded by different Ca2+ signatures like Ca2+ sensors, Calmodulins (CaM), Calmodulin-like proteins (CMLs), Ca2+ -dependent protein kinases (CDPKs), Calcineurin B-like proteins (CBLs) and their interacting kinases (CIPKs) in plants. A fluctuation in response to an external or extracellular stimulus increases the cytoplasmic calcium [Ca2+](cyt) concentration. This increase in Ca2+ concentration is sensed by proteins present in the cell, and these proteins interact with increasing Ca2+ ions and lead to change in the conformation of proteins from closed to open and allow other signal transduction molecules for binding and activation. The proteins which bind with Ca2+ are called Ca2+-binding proteins or Ca2+ sensors (with or without EF-hand motif). Ca2+ sensors like CDPK regulate the expression of genes under various abiotic and biotic stresses. Ca2+ regulates the cell cycle by participating in nuclear envelope breakdown and reformation, cleavage furrow formation, and cell plate formation. Ca2+ signaling also cross-talk with other signaling molecules like reactive oxidative species (ROS), MAPKs, ABA, nitric oxide (NO), and osmolytes, results in massive stress response. External stimuli like light, heat, drought, salinity, cold, chemical, or elicitor released after the pathogenic attack, etc. are responsible for activation of Ca2+ signaling. Ca2+ influx is usually a diffusion process through channels, so there is no need for energy, but through the transporter, the influx of Ca2+ requires energy in the form of ATP. Active transport of Ca2+ takes place via Ca2+-ATPase and H+-Ca2+ antiporter. This review describes the importance of Ca2+ signaling, Ca2+ channels, Ca2+ transporters, Ca2+ sensors, and EF-hand motif in plants to cope with various environmental cues. (c) 2022 SAAB. Published by Elsevier B.V. All rights reserved.