Heterologous co-expression of a yeast diacylglycerol acyltransferase () and a plant oleosin () as an efficient tool for enhancing triacylglycerol accumulation in the marine diatom .

Background: Microalgae are promising alternate and renewable sources for producing valuable products such as biofuel and essential fatty acids. Although this is the case, there are still challenges impeding on the effective commercial production of microalgal products. For instance, their product yield is still too low. Therefore, this study was oriented towards enhancing triacylglycerol (TAG) accumulation in the diatom (strain Pt4). To achieve this, a type 2 acyl-CoA:diacylglycerol acyltransferase from yeast () and the lipid droplet (LD) stabilizing oleosin protein 3 from () were expressed in Pt4.

Results: The individual expression of and in Pt4 resulted in a 2.3- and 1.4-fold increase in TAG levels, respectively, in comparison to the wild type. The co-expression of both, and , was accompanied by a 3.6-fold increase in TAG content. On the cellular level, the lines co-expressing and showed the presence of the larger and increased numbers of lipid droplets when compared to transformants expressing single genes and an empty vector. Under nitrogen stress, TAG productivity was further increased twofold in comparison to nitrogen-replete conditions. While TAG accumulation was enhanced in the analyzed transformants, the fatty acid composition remained unchanged neither in the total lipid nor in the TAG profile.

Conclusions: The co-expression of two genes was shown to be a more effective strategy for enhancing TAG accumulation in strain Pt4 than a single gene strategy. For the first time in a diatom, a LD protein from a vascular plant, oleosin, was shown to have an impact on TAG accumulation and on LD organization.