The UV-A receptor CRY-DASH1 regulates ciliary length and mating efficiency in Chlamydomonas reinhardtii

The biflagellate green alga Chlamydomonas reinhardtii encodes two DASH ( Drosophila , Arabidopsis , Synechocystis , Homo )-type cryptochromes. One of them, CRY-DASH1, absorbs mainly in the UV-A area and is localized in the chloroplast. Previous studies have shown that CRY-DASH1 balances the photosynthetic machinery. It acts as a repressor of chlorophyll and carotenoid biosynthesis as well as of thylakoid membrane hyperstacking and it is an activator of specific pathways of the central carbon metabolism and of histidine biosynthesis. Environmental conditions influence the expression of CRY-DASH1; in addition, such conditions cause variations in the length of the algal cilia (also known as flagella). Here, we analyzed whether CRY-DASH1 may be involved in regulating the length of the cilia in C. reinhardtii by using wild-type cells and a backcrossed cry-dash1 knock-out mutant ( cry-dash1 mut ). We find that the ciliary length is significantly increased in vegetative cells of cry-dash1 mut compared to wild-type cells. Frequency distribution histograms suggest that the ciliary length of the entire algal population has shifted toward the longer values. According to prior findings, we corroborate that the ciliary length of C. reinhardtii wild-type gametes is increased compared to that of vegetative wild-type cells. Cilia of cry-dash1 mut cells are even further lengthened. Moreover, we find that the mating efficiency of plus and minus gametes of cry-dash1 mut strains is enhanced. All phenotypes were rescued to a significant extent in partially complemented CRY-DASH1 lines. Our results demonstrate that CRY-DASH1 is involved in the regulation of ciliary length in vegetative cells and gametes across the entire population. As cilia get longer in cry-dash1 mut , CRY-DASH1 acts as a repressor of ciliary length. Additionally, CRY-DASH1 functions as a negative regulator of mating efficiency in C. reinhardtii . Together, these findings expand the known functional roles of CRY-DASH1 beyond photosynthetic and metabolic regulation and suggest a relationship between photoreceptor-associated regulation and ciliary-associated cellular processes in this green alga.