The evolution of Ca2+ signalling in photosynthetic eukaryotes

Summary It is likely that cytosolic Ca2+ elevations have played a part in eukaryotic signal transduction for about the last 2 Gyr, being mediated by a group of molecules which are collectively known as the [Ca2+]cyt signalling toolkit. Different eukaryotes often display strikingly similar [Ca2+]cyt signalling elevations, which may reflect conservation of toolkit components (homology) or similar constraints acting on different toolkits (homoplasy). Certain toolkit components, which are presumably ancestral, are shared by plants and animals, but some components are unique to photosynthetic organisms. We propose that the structure of modern plant [Ca2+]cyt signalling toolkits may be explained by their modular adaptation from earlier pathways. Contents Summary 21 I. Introduction 21 II. Homology vs homoplasy 22 III. The structure and variation of [Ca2+]cyt signalling pathways 27 IV. A putative course of descent for plant [Ca2+]cyt signalling 29 V.