Calcium Signalling in Plants

Abstract

Ca2+ is an important signal transduction molecule that has been shown to regulate responses to a large number of environmental stimuli in plants and control many developmental processes. These stimuli induce the formation of Ca2+ signals within a cell, which are generated through the action of Ca2+ release and uptake from and into internal cellular stores or the apoplast by the activity of Ca2+ channels, pumps and exchangers. These signals take the form of elevations of Ca2+ with specific spatio‐temporal characteristics which are thought to denote the initial stimulus and mediate an appropriate cellular response. Information is therefore hypothesised to be encoded in these signals, which are decoded and relayed to downstream gene expression regulators and protein kinases via an array of Ca2+‐binding sensor proteins.

Key Concepts:

  • Calcium signals allow plants to specifically sense and respond to environmental stimuli.

  • Calcium signals are generated through the coordinated action of calcium influx channels and calcium efflux transporters.

  • A large network of calcium‐binding proteins act as calcium sensors and relay calcium signals to downstream effector proteins.

Keywords: Arabidopsis; calcium; calcium transport; calmodulin; protein kinases; signal transduction; transcription factors

Figure 1.

Schematic highlighting the key steps in Ca2+ signalling pathways. Stimuli such as pathogen elicitors, ABA, H2O2 and cold, show specific cytosolic Ca2+ signatures after influx of Ca2+. Ca2+ binds to sensors such as calmodulin (CaM), CaM‐like proteins (CML), calcium‐dependent protein kinases (CDPK), and calcineurin B‐like proteins (CBL) (which forms a complex with Ca2+‐independent protein kinase (CIPK)). Ca2+ sensors activate transcription factors (TF) and other proteins either by direct binding or through phosphorylation (P). TFs bind DNA and cause up‐ or down‐regulation of gene expression. CAMTA, CaM‐binding transcription activator; CBP60, CaM‐binding protein; TGA, basic leucine zipper (bZIP) transcription factor; MYB, plant homologue of animal myeloblastosis TFs; WRKY, TF with conserved domain containing these amino acids.

Figure 2.

The distribution of Ca2+ transporters within a typical plant cell. Plants possess Ca2+‐permeable influx channels (blue rectangles), as well as vacuolar Ca2+/H+ exchangers (green cylinder) and Ca2+ pumps (red ovals) for extruding Ca2+. All named proteins are from Arabidopsis thaliana. ACA, autoinhibited Ca2+‐ATPase; CAX, Ca2+/H+ exchanger; CNGC, cyclic nucleotide gated channel; DACC, depolarisation‐activated Ca2+ channel; ECA, ER‐type Ca2+‐ATPase; GLR, glutamate receptor‐like channel; HACC, hyperpolarisation‐activated Ca2+ channel; IP3R‐like, inositol‐1,4,5‐trisphosphate receptor‐like channel; MCC, mechanosensitive Ca2+ channel; NAADPR, nicotinic acid adenine dinucleotide phosphate receptor channel; RyR‐like, cyclic ADP‐ribose‐activated ryanodine receptor‐like channel; TPC, two‐pore channel, a slow‐activating vacuolar (SV) Ca2+ channel; VVCC, vacuolar voltage‐gated Ca2+ channel. Courtesy of Dr. James Connorton.

Figure 3.

Putative pathways for pathogen‐mediated, Ca2+‐dependent activation of plant defence responses. Binding of an elicitor (AtPep) to a receptor (AtPepR1) activates adenylyl cyclase (AC) and/or guanylyl cyclase (GC), which generate cAMP or cGMP, respectively. Increase in cAMP and cGMP concentration activates cyclic nucleotide gated channels (CNGC), which causes influx of Ca2+ into the cytosol. Ca2+ binding to calmodulin (CaM) and calcium‐dependent protein kinases (CDPK) indirectly activates the hypersensitive response (HR), defence‐related gene expression and increased salicylic acid (SA) production. CaM activates NO synthase, producing NO which acts in conjunction with H2O2 generated from CDPK‐activated NADPH oxidase in order to stimulateHR and gene expression. CaM binding to transcription factors (TF) (e.g. CAMTA, WRKY and CBP60) activates gene expression, while CDPK may phosphorylate TFs which can then bind to DNA (dashed arrows). Red line depicts inhibition of CNGC activity by Ca2+/CaM.

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How to Cite close
Bickerton, Peter D, and Pittman, Jon K(May 2012) Calcium Signalling in Plants. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0023722]