Calcium channels in photosynthetic eukaryotes: implications for evolution of calcium‐based signalling

Contents   Summary 23 I. Introduction 24 II. Physiological features of Ca2+ channel activity ineukaryotic photoautotrophs 25 III. Expansion, loss and horizontal gene transfer of Ca2+-permeable channels in photoautotrophs 28 IV. Conclusions 36   Acknowledgements 37   References 37 Summary Much of our current knowledge on the mechanisms by which Ca2+ signals are generated in photosynthetic eukaryotes comes from studies of a relatively small number of model species, particularly green plants and algae, revealing some common features and notable differences between ‘plant’ and ‘animal’ systems. Physiological studies from a broad range of algal cell types have revealed the occurrence of animal-like signalling properties, including fast action potentials and fast propagating cytosolic Ca2+ waves. Genomic studies are beginning to reveal the widespread occurrence of conserved channel types likely to be involved in Ca2+ signalling. However, certain widespread ‘ancient’ channel types appear to have been lost by certain groups, such as the embryophytes. More recent channel gene loss is also evident from comparisons of more closely related algal species. The underlying processes that have given rise to the current distributions of Ca2+ channel types include widespread retention of ancient Ca2+ channel genes, horizontal gene transfer (including symbiotic gene transfer and acquisition of bacterial genes), gene loss and gene expansion within taxa. The assessment of the roles of Ca2+ channel genes in diverse physiological, developmental and life history processes represents a major challenge for future studies.