Calcium decoders and their targets: The holy alliance that regulate cellular responses in stress signaling

Calcium (Ca²⁺) signaling is versatile communication network in the cell. Stimuli perceived by cells are transposed through Ca²⁺-signature, and are decoded by plethora of Ca²⁺ sensors present in the cell. Calmodulin, calmodulin-like proteins, Ca²⁺-dependent protein kinases and calcineurin B-like proteins are major classes of proteins that decode the Ca²⁺ signature and serve in the propagation of signals to different parts of cells by targeting downstream proteins. These decoders and their targets work together to elicit responses against diverse stress stimuli. Over a period of time, significant attempts have been made to characterize as well as summarize elements of this signaling machinery. We begin with a structural overview and amalgamate the newly identified Ca²⁺ sensor protein in plants. Their ability to bind Ca²⁺, undergo conformational changes, and how it facilitates binding to a wide variety of targets is further embedded. Subsequently, we summarize the recent progress made on the functional characterization of Ca²⁺ sensing machinery and in particular their target proteins in stress signaling. We have focused on the physiological role of Ca²⁺, the Ca²⁺ sensing machinery, and the mode of regulation on their target proteins during plant stress adaptation. Additionally, we also discuss the role of these decoders and their mode of regulation on the target proteins during abiotic, hormone signaling and biotic stress responses in plants. Finally, here, we have enumerated the limitations and challenges in the Ca²⁺ signaling. This article will greatly enable in understanding the current picture of plant response and adaptation during diverse stimuli through the lens of Ca²⁺ signaling.