Spatiotemporal Cytosolic Ca2+ Signals in Plants and Algae: Divergent Means to an End

The ability to generate distinct spatiotemporal patterns of cytosolic calcium concentration (Ca-cyt(2+)) is a fundamental property of eukaryotic cells and underlies responses to external stimuli as well as directing downstream processes involved in morphogenesis, growth, and even developmental fate. In this review, we consider a number of well-studied and less well-studied photosynthetic plant and algal systems from the point of view of the different Ca2+ channel types that underlie spatiotemporal Ca-cyt(2+) patterns. These include pollen tubes, root hairs, moss protonema, algal rhizoids, and single-celled algae. We show that similar spatial and temporal Ca-cyt(2+) patterns can be brought about by the coordinated activities of a range of Ca2+ channel types. Most significantly, these channel types vary widely between different photosynthetic groups, indicating that the conserved necessity to generate spatiotemporal Ca2+ signals is satisfied by divergent underlying mechanisms, likely reflecting the different evolutionary pressures on ion transport mechanisms across the photosynthetic eukaryote clades.