Heterologous phospholipid:diacylglycerol acyltransferase enhances triacylglycerol accumulation without compromising growth in Nannochloropsis oceanica

Nannochloropsis oceanica, an industrially important single-cell factory for lipid production, can accumulate a vast amount of triacylglycerol (TAG) due to multiple acyl CoA:diacylglycerol acyltransferases and a single-copy phospholipid:diacylglycerol acyltransferase (NoPDAT). NoPDAT uses mainly phosphatidylethanolamine (PE) and phosphatidylglycerol with 16:0, 16:1, and 18:1 as acyl-donors so that only trace eicosapentaenoic acid (EPA) is transferred from the polar lipids to TAG. In this study, a Phaeodactylum tricornutum PDAT (PtPDAT) was heterologously expressed in N. oceanica to increase the EPA content in TAG. Heterologous expression of PtPDAT did not disturb the growth of the transgenic lines while enhancing the TAG content by 28–30 % as quantified by the acyl chains on day 10. Heterologously expressed PtPDAT was localized in the plastid inner membrane of N. oceanica, consistent with its original localization in P. tricornutum. However, the substrate preference of PtPDAT was changed from phosphatidylcholine to EPA-enriched PE in N. oceanica, thus increasing the EPA content in TAG by 20–51 % in the transgenic lines. This study demonstrates the potential of an efficient acyl editing in N. oceanica by heterologous PDAT gene.