The multiple routes of photosynthetic electron transfer in Chlamydomonas reinhardtii

International audience; Like all organisms performing oxygenic photosynthesis, Chlamydomonas captures light energy in two photochemical steps to drive linear electron flow from water to NADPH and to produce ATP. However, this process alone is not sufficient to drive CO2 fixation in the Calvin–Benson cycle and to respond to environmental and metabolic constraints, for example, light availability or metabolic needs in term of ATP and NADPH. A complex network of alternative electron flows, comprises cyclic electron flow around photosystem I and various water-to-water cycles that utilize O2 as an alternative electron acceptor, provide an additional degree of freedom to face this challenge. The present chapter describes the various alternative routes of photosynthetic electron transfer in Chlamydomonas, describes how they are coordinated for optimization of photosynthesis and gives a retrospective on the early physiology work on those alternative electron flows among model photosynthetic organisms.