Decrypting calcium signaling in plants: The kinase way

Abstract

Ca2+ is an indispensible messenger in cellular signaling for all eukaryotes. Plants respond to modulation in Ca2+ concentration, known as "Ca2+ signatures," which are induced in response to extrinsic and intrinsic cues. These Ca2+ signatures are perceived, decoded, and transduced to downstream response toolkit comprising of a complex group of Ca2+-binding proteins that function as Ca2+ sensors. Ca2+-dependent protein kinase (CPK), Ca2+ or Ca2+/calmodulin-dependent protein kinase (CCaMK), calcineurin B-like protein (CBL), and their interacting kinases (CIPK) are directly or indirectly regulated by Ca2+. These Ca2+-regulated kinases are part of phosphorylation pathway that lead to regulation of ion channels, v-SNARE proteins, nitrate sensing, nodulation, and transcriptional factors for master regulation. Genome sequencing data of wide varieties of plant species along with high-throughput transcriptomic and functional genomic analysis has expedited revealing of multifaceted functions of these kinases in stress-signaling networks. Combining the transcriptomic and posttranscriptional proteomic regulatory mechanisms in CDPKs and CBL-CIPKs reveals an emerging evolutionary model. Subcellular proteomics and varying affinity for Ca2+ emerged as a crucial regulatory mechanism for transducing stress signal. Cross talk of isoforms and their interacting partners adds on to the humongous effect on increasing complexities among these signaling cascades. This chapter provides new insight about the colossal advancement in understanding of the regulatory mechanism and functionality involved in Ca2+ sensing by kinases in light of the information generated by genomic tools.