Expression of Chlamydomonas reinhardtii chloroplast diacylglycerol acyltransferase 3 is induced by light in concert with triacylglycerol accumulation

SUMMARY Considerable progress has been made towards the understanding of triacylglycerol (TAG) accumulation in algae. One key aspect is finding conditions that trigger TAG production without reducing cell division. Previously, we identified a soluble diacylglycerol acyltransferase (DGAT), related to plant DGAT3, with heterologous DGAT activity. In this work, we demonstrate that Chlamydomonas reinhardtii DGAT3 localizes to the chloroplast and that its expression is induced by light, in correspondence with TAG accumulation. Dgat3 mRNAs and TAGs increase in both wild‐type and starch‐deficient cells grown with acetate upon transferring them from dark or low light to higher light levels, albeit affected by the particularities of each strain. The response of dgat3 mRNAs and TAGs to light depends on the pre‐existing levels of TAGs, suggesting the existence of a negative regulatory loop in the synthesis pathway, although an effect of TAG turnover cannot be ruled out. Altogether, these results hint towards a possible role of DGAT3 in light‐dependent TAG accumulation in C. reinhardtii. Significance Statement In Chlamydomonas reinhardtii, an increase in TAG content occurs under both moderate and saturating light levels, and this accumulation agrees with the expression of DGAT3, the first algal DGAT reported to localize to the chloroplast. This response depends on the pre‐existing levels of TAGs, which suggests the existence of negative feedback in the TAG synthesis pathway. Taken together, these results have relevant implications for the accumulation of photosynthetic overflow products.