Abstract
The Ca2+ ion is recognized as a crucial second messenger in signaling pathways coupling the perception of environmental stimuli to plant adaptive responses. Indeed, one of the earliest events following the perception of environmental changes (temperature, salt stress, drought, pathogen, or herbivore attack) is intracellular variation of free calcium concentrations. These calcium variations differ in their spatio-temporal characteristics (subcellular location, amplitude, kinetics) with the nature and strength of the stimulus and, for this reason, they are considered as signatures encrypting information from the initial stimulus. This information is believed to drive a specific response by decoding via calcium-binding proteins. Based on recent examples, we illustrate how individual calcium sensors from the calcium-dependent protein kinase and calmodulin-like protein families can integrate inputs from various environmental changes. Focusing on members of these two families, shown to be involved in plant responses to both abiotic and biotic stimuli, we discuss their role as key hubs and we put forward hypotheses explaining how they can drive the signaling pathways toward the appropriate plant responses.
Highlights
Plants as sessile organisms have to continuously face environmental cues coming from abiotic and biotic challenges
Calcium sensor proteins estimated to number over 250 in Arabidopsis (Day et al, 2002) are represented by three main families, i.e., the calcineurin-Blike proteins (CBLs) (Luan, 2009), the calmodulin (CaM), and calmodulin-like proteins (CMLs) (Yang and Poovaiah, 2003; Bender and Snedden, 2013), the calcium-dependent protein kinases (CPKs) and the calcium and calmodulin-dependent protein kinase (CCaMK) (Cheng et al, 2002; Wang et al, 2015)
In addition to CaM, which has been well conserved through evolution, plant genomes are predicted to encode a broad range of CML proteins (McCormack et al, 2005; Boonburapong and Buaboocha, 2007; Zhu et al, 2015)
Summary
Plants as sessile organisms have to continuously face environmental cues coming from abiotic and biotic challenges. Calcium sensor proteins estimated to number over 250 in Arabidopsis (Day et al, 2002) are represented by three main families, i.e., the calcineurin-Blike proteins (CBLs) (Luan, 2009), the calmodulin (CaM), and calmodulin-like proteins (CMLs) (Yang and Poovaiah, 2003; Bender and Snedden, 2013), the calcium-dependent protein kinases (CPKs) and the calcium and calmodulin-dependent protein kinase (CCaMK) (Cheng et al, 2002; Wang et al, 2015) These proteins display various affinities for calcium ions and this property, combined with their sub-cellular location within the cell, will control their behavior. We will discuss how a single Ca2+ sensor may direct the flow of signaling information toward distinct adaptive responses
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