Decoding and relay of Calcium signals in plants

Abstract

Calcium is an essential macronutrient and a second messenger for signal transduction in plant. Apart from acting as a second messenger calcium is also required for cytoskeleton, cell division, pollen tube growth and as cofactors. Cytoplasmic calcium ion ([Ca²⁺]_cyt) is maintained at a low level, however, rapidly elevated using storages in organelles on perception of a stimulus. Ca²⁺-binding proteins that sense the kinetics and magnitude of elevated [Ca²⁺]_cyt convert the chemical signals to biological signals and define specificity of responses. These proteins are broadly classified into sensor relays and sensor responders. Sensor relay proteins require another interacting protein to transmit the signal; whereas the sensor responders combine within one protein the relay, amplification and response functions. A significant achievement has been made in last three decades that identified and characterized various proteins instrumental in decoding Ca²⁺-signals in plant cells. It is believed that flexibility of interactions between these proteins and their sub-cellular localizations are crucial in sensing and responding to specific signals. The latest addition in Ca²⁺-signalling is Calcineurin B-like proteins (CBLs) and their interacting kinases (CIPKs). In this review, we have laid an emphasis in the recent and emerging advancements in the understanding of CBL-CIPK module.