Calcium signaling in coordinating plant development, circadian oscillations and environmental stress responses in plants

Calcium (Ca 2+ ) is an intracellular second messenger involved in many signal transduction pathways in plants. The perception of environmental and internal cues leads to alterations in the cytosolic Ca 2+ signatures which translate into changes in gene expression and cellular functions. Herein, we review the novel roles of Ca 2+ signalling in coordinating plant stem cell niche homeostasis for root and shoot development. We also summarize the regulatory networks between Ca 2+ signalling and other plant signalling pathways which commence into activation or repression of genes involved in regulating vegetative to reproductive phase transition and light-mediated plant growth responses. The possible functions of Ca 2+ in the input pathway as a second messenger, external stimuli and the output of the clock regulating the rhythmicity of the plant circadian system are being reviewed. Additionally, we have also highlighted the new insights into the roles of Ca 2+ signalling components in the perception and regulation of abiotic/ biotic stress responses in plants. • Ca 2+ signalling integrates several signalling pathways in response to various environmental stimuli in plants. • Nuclear Ca 2+ signalling correlates cell activity, plant development, developmental phase transition, and hormonal homeostasis. • Ca 2+ signalling plays crucial roles in coordinating phosphorylation-mediated photoacclimation processes in plants. • Cytosolic-free Ca 2+ oscillations regulate circadian clocks in plants through Ca 2+ dependent calcium binding proteins. • Spatiotemporal regulation of Ca 2+ binding proteins couple biotic/abiotic stress responses contributing towards plant adaptation.