Cryptochrome photoreceptors in the green alga Chlamydomonas reinhardtii : versatility of functions and mechanisms Photosynthetic microorganisms including microalgae and cyanobacteria account to half of global CO2 fixation. Light governs their photosynthesis and other biological functions. Specifically cryptochromes photoreceptors found universally primarily detect UV A blue light and are known to repair DNA. This study focuses on five algal cryptochromes especially CRY DASH1 (Drosophila Arabidopsis Synechocystis Homo) in the green alga Chlamydomonas reinhardtii. Located in the chloroplast CRY DASH1s expression peaks around midday. A mutant lacking CRY DASH1 showed decreased growth but enhanced photosynthesis efficiency. Furthermore the mutant revealed increased pigment amounts hyper stacking of the thylakoid membrane and elevated levels of photosystem II proteins like D1 and CP43 but not of their transcripts. These data suggest that CRY DASH1 plays its role as regulator at the posttranscriptional translational level. CRY DASH1 has an absorption peak in the UV A range and supplementation of white light with UV A increases photoautotrophic growth of wild type but not of the mutant lacking CRY DASH1. Comparative analysis of the chloroplast proteome of wild type and of the mutant revealed that multiple proteins including key enzymes for the synthesis of chlorophylls and carotenoids as well as acyl lipid metabolism and photoprotection are upregulated in the mutant. In contrast we found that essential proteins from the central carbon metabolism are downregulated. Additionally we discovered that the mutant revealed a downregulation of certain enzymes involved in histidine metabolism which leads to a reduction in the quantity of free histidine. Another cryptochrome CRY DASH2 when mutated exhibited similar growth reduction and pigment increase. The study ends pondering if CRY DASH1 and CRY DASH2 might have overlapping functionalities.