Calcium-Dependent Signalling Processes in Chlamydomonas

Abstract

Like all organisms, the motile green alga Chlamydomonas has evolved an array of sensory mechanisms to enable it to detect and respond to an array of abiotic and biotic stimuli. It is clear that Ca²⁺-dependent signalling mechanisms are central to many responses in Chlamydomonas, from flagella function through to stress signalling and photosynthesis. Chlamydomonas has long been used as a model organism for flagella function and this aspect of signalling has received much attention, with well-characterised roles for Ca²⁺ in flagella beat, phototaxis, mating and deflagellation. Recent progress has identified a series of ion channels and Ca²⁺-sensor kinases that underpin these responses and direct imaging of flagella Ca²⁺ in Chlamydomonas cells has demonstrated the highly dynamic nature of Ca²⁺ signalling in these organelles. The role of Ca²⁺ in other signalling processes in Chlamydomonas has been less well explored, although exciting recent developments have demonstrated novel Ca²⁺-dependent signalling processes associated with the regulation of photosynthesis. These developments highlight the diverse roles of Ca²⁺ in Chlamydomonas physiology and the potential for the discovery of novel Ca²⁺ signalling mechanisms within this organism.