From Prokaryotes to Eukaryotes: Insights into the Structure, Function, and Evolution of Phytoene Synthases

Phytoene synthase (PSY) catalyzes the committed and rate-limiting step in carotenoid biosynthesis by condensing two geranylgeranyl diphosphate molecules into 15-<i>cis</i>-phytoene. As the gateway enzyme, PSY directs metabolic flux toward diverse carotenoids, which functions as essential pigments, antioxidants, and provitamin A precursors in nutrition and agriculture. PSY enzymes, widespread across biological kingdoms, have evolved lineage-specific regulatory mechanism while retaining conserved catalytic features, including hydrophobic loops and Asp-rich motifs, indicating a universal synthesis mechanism. This review summarizes evolutionary phylogeny and structure-function relationship of PSYs from prokaryotes to eukaryotes, highlighting their roles as key biotechnological targets for metabolic engineering to improve crop nutritional quality, stress resilience, and biofortification. Future research should elucidate PSY's regulation, catalytic machinery, and rate-limiting control over carotenoid profiles.