MOLECULAR MECHANISM OF β-CAROTENE HYDROXYLASE IN REGULATION OF PHOTOPROTECTION AND COORDINATED FLAGELLAR BEATING IN CHLAMYDOMONAS REINHARDTII

To investigate the function and mechanism of β-carotene hydroxylase (CHYB) in <italic>Chlamydomonas reinhardtii</italic>, CRISPR/Cas9-mediated gene editing was used to precisely knockout <italic>CHYB</italic> gene from <italic>Chlamydomonas reinhardtii</italic> and successfully isolated the <italic>chyb</italic> mutants. Phenotypic analysis revealed that <italic>CHYB</italic> knockout significantly decreased photosynthetic activity of photosystem II (PSII), light utilization efficiency (Alpha), and photosynthetic electron transport rate (ETR_max) in <italic>chyb</italic> mutants, ultimately reducing cell growth rate. Under high light conditions, the photoprotection related non-photochemical quenching ability of <italic>chyb</italic> mutants was inhibited. Targeted metabolomics analysis revealed the contents of zeaxanthin, antheraxanthin, and violaxanthin, which were the key components of the xanthophyll cycle, were significantly reduced in <italic>chyb</italic> mutants, thereby affecting the photoprotection ability of <italic>Chlamydomonas reinhardtii</italic>. In addition, mutations in the <italic>CHYB</italic> gene were found to affect flagellar beating coordination, resulting in the inability of <italic>Chlamydomonas reinhardtii</italic> to sustain linear movement. These findings establish dual physiological roles of <italic>CHYB</italic> in <italic>Chlamydomonas reinhardtii</italic>: (1) maintaining the non-photochemical quenching ability of <italic>Chlamydomonas reinhardtii</italic> by regulating the synthesis of key components of xanthophyll cycle; (2) potentially regulating flagellar beating coordination via carotenoid synthesis in eyespots. These findings provide novel insights into the role of carotenoids in regulating the environmental adaptability of photosynthetic organisms.