TypiCal but DeliCate Ca(++)re: Dissecting the Essence of Calcium Signaling Network as a Robust Response Coordinator of Versatile Abiotic and Biotic Stimuli in Plants

Plant growth, development, and ultimately crop productivity are largely impacted by the interaction of plants with different abiotic and biotic factors throughout their life cycle. Perception of different abiotic stresses, such as salt, cold, drought, heat, and heavy metals, and interaction with beneficial and harmful biotic agents by plants lead to transient, sustained, or oscillatory changes of [calcium ion, Ca(2+)](cyt) within the cell. Significant progress has been made in the decoding of Ca(2+) signatures into downstream responses to modulate differential developmental and physiological responses in the whole plant. Ca(2+) sensor proteins, mainly calmodulins (CaMs), calmodulin-like proteins (CMLs), and others, such as Ca(2+)-dependent protein kinases (CDPKs), calcineurin B-like proteins (CBLs), and calmodulin-binding transcription activators (CAMTAs) have played critical roles in coupling the specific stress stimulus with an appropriate response. This review summarizes the current understanding of the Ca(2+) influx and efflux system in plant cells and various Ca(2+) binding protein-mediated signal transduction pathways that are delicately orchestrated to mitigate abiotic and biotic stresses. The probable interactions of different components of Ca(2+) sensor relays and Ca(2+) sensor responders in response to various external stimuli have been described diagrammatically focusing on established pathways and latest developments. Present comprehensive insight into key components of the Ca(2+) signaling toolkit in plants can provide an innovative framework for biotechnological manipulations toward crop improvability in near future.