A Photoperiod-Regulating Gene CONSTANS Is Correlated to Lipid Biosynthesis in Chlamydomonas reinhardtii

Background. The regulation of lipid biosynthesis is essential in photosynthetic eukaryotic cells. Thus far, no regulatory genes have been reported in the lipid metabolism pathway. Plant CONSTANS (CO) gene regulates blooming by participating in photoperiod and biological clock. Apart from regulating photoperiod, the Chlamydomonas CO gene also regulates starch content. Results. In this study, the results showed that, under HSM-S condition, cells accumulated more lipids at short-day conditions than at long-day conditions. The silencing of the CrCO gene via RNA interference resulted in an increase in lipid content and an increase in triacylglyceride (TAG) level by 24.5%. CrCO RNAi strains accumulated more lipids at short-day conditions than at long-day conditions. The decrease in CrCO expression resulted in the increased expression of TAG biosynthesis-related genes, such as DGAT2, PAP2, and PDAT3, whereas CIS and FBP1 genes showed a decrease in their mRNA when the CrCO expression was suppressed. On the other hand, the overexpression of CrCO resulted in the decrease in lipid content and TAG level. Conclusions. The results of this study revealed a relationship between CrCO gene and lipid metabolism in Chlamydomonas, suggesting that increasing oil by suppressing CrCO expression in microalgae is feasible.