Cryptochrome photoreceptors in the green alga Chlamydomonas reinhardtii: Versatility of functions and mechanisms

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Microalgae live in the ocean, freshwater and/or wet soil. They contribute significantly to global carbon fixation and are at the basis of food webs. To cope with the different intensities and qualities of light in the water column, they developed a large variety of photoreceptors with novel functions and mechanisms. The biflagellate green unicellular alga Chlamydomonas reinhardtii serves since decades as a model to study light-driven processes, since it can be transformed and genetic crosses are possible such as with baker’s yeast. Light influences its behavior, its life cycle, photosynthesis and synchronizes its circadian clock by light-dark cycles. C. reinhardtii has 18 different putative photoreceptors and from some of them we do not know any function or mechanism of action. Four of these receptors belong to the cryptochrome (CRY) family that derives from DNA repair enzymes (photolyases), including a typical plant CRY (pCRY) as found in higher plants, an animal-like CRY (aCRY) as well as two DASH-like CRYs. In this proposal, we aim to study further the functions and mechanisms of the green algal cryptochromes. We are interested in (a) the mechanism of degradation of aCRY during the sexual cycle of the alga and its influence on the life cycle as well as in (b) the interaction partner(s) of pCRY in the night and their contribution to circadian and/or life cycle regulation as well as in (c) the functions of the still elusive roles of the two CRY-DASHs. Insertional knock-down and know out mutants are available for this purpose and CRISPR/Cas9 approaches can be used for generating further mutants. We want to understand how the variety of cryptochrome photoreceptors along with their different absorption spectra controls algal life and aim to reveal the overlapping as well as the distinct functions of the different cryptochromes.