Overexpression of DnaJ-Like Chaperone Enhances Carotenoid Synthesis in Chlamydomonas reinhardtii

Production of functional carotenoids using microalgae may facilitate the commercialization of anti-aging nutritional supplements. The green alga Chlamydomonas reinhardtii uses a non-mevalonate (MEP) pathway for isopentenyl diphosphate (IPP) synthesis. Two enzymes thought to play important roles in this MEP pathway to IPP synthesis are 1-deoxy-d-xylulose 5-phosphate synthase (DXS) and reductase (DXR). DnaJ-like chaperone (Orange protein) is thought to support phytoene synthase, a key enzyme in plant carotenoid synthesis. Genes for Orange (OR), DXS, and DXR were overexpressed via nuclear transformation into C. reinhardtii. CDS of OR, DXS, and DXR were amplified and connected with dual promoters of heat-shock protein 70A and ribulose bisphosphate carboxylase small chain 2. Compared with the parental strain, transformant CrOR#2 produced increased lutein and beta-carotene (1.9-fold and 1.7-fold per cell, respectively). Transformant CrDXS#1 produced lutein and beta-carotene at lower per-cell abundances than those for the parental strain. CrDXR#2 transformant produced lutein and beta-carotene at higher per-cell abundances than their parental counterpart; however, these transformants produced lutein and beta-carotene at lower per-medium abundances than their parental counterparts. These results suggest that OR protein supports phytoene synthase in C. reinhardtii and that the phytoene synthesis step is rate-limiting in carotenoid synthesis.