Phototropin connects blue light perception to starch metabolism in green algae

In photosynthetic organisms light acts as an environmental signal to control their development and physiology, and as energy source to drive the conversion of CO2 into carbohydrates used for growth or storage. The main storage carbohydrate in green algae is starch, which accumulates during the day and is broken down at night to meet cellular energy demands. The signalling role of light quality in the regulation of starch accumulation remains unexplored. Here, we report that in the model green alga Chlamydomonas reinhardtii blue light perceived by the photoreceptor PHOTOTROPIN causes dephosphorylation of the PHOTOTROPIN-MEDIATED SIGNALLING KINASE 1 that then suppresses starch accumulation by inhibiting the expression of GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE. Our results provide an in-depth view of how photoreceptor-mediated signalling controls microalgal carbon metabolism.