Whole genome sequencing of Chromochloris zofingiensis UV-mutants to identify glucose-linked phenotype

In this study, we investigated the regulation of photosynthesis and metabolism in C. zofingiensis in response to exogenous glucose. Through a forward genetics screen coupled to whole genome sequencing, we uncovered hexokinase1 (CzHXK1) as a master regulator of photosynthesis, carbon metabolism, and ketocarotenoid (astaxanthin) biosynthesis in C. zofingiensis. The hxk1 mutants are deficient in turning off photosynthesis and accumulating astaxanthin and lipids in the presence of glucose. HXK, a key enzyme in carbon metabolism, generates glucose-6-phosphate (G6P) that can be used in a variety of pathways including glycolysis, the oxidative pentose phosphate pathway, and starch and cell wall biosynthesis. HXK is also known to be an evolutionarily conserved eukaryotic glucose sensor in yeast and plants. In contrast to yeast and plants, C. zofingiensis has a single gene encoding hexokinase. Thus, our work establishes C. zofingiensis as a relatively simple system in which to investigate conserved mechanisms of sugar sensing and signaling in the green lineage.