Manipulation of triacylglycerol biosynthesis in Nannochloropsis oceanica by overexpressing an Arabidopsis thaliana diacylglycerol acyltransferase gene

Abstract

Given the depleting fossil fuel resource, oleaginous microalgae have a great potential as feedstocks for sustainable and environment-friendly biofuels. Improvement of neutral lipid, especially triacylglycerol (TAG), accumulation, without a cost of growth is considerably desirable for the commercial feasibility of microalgae-derived biofuels. Genetic engineering emerges as a feasible and effective strategy to achieve this goal. Diacylglycerol acyltransferase (DGAT) catalyzes the committed and final step in the de novo biosynthesis pathway of TAG. Nevertheless, the effectiveness of overexpression of plant-derived DGAT gene in Nannochloropsis sp. remains obscure. In this study, the type1 DGAT gene (AtDGAT) from Arabidopsis thaliana was heterogeneously expressed in Nannochloropsis oceanica by electroporation, yielding one AtDGAT transformant (N4 strain). The integration and transcription of AtDGAT in N. oceanica cells were confirmed by PCR. Results revealed that HSP70A-RBSC2 promoter could activate AtDGAT transcription in N. oceanica treated with or without heat shock. AtDGAT transcription in N4H cells (with heat shock) was 31.25 times as high as that in N4 cells (without heat shock). The overexpression of AtDGAT in N. oceanica led to a significant increase in total lipid and TAG contents without compromising algal growth. In addition, gas chromatography–mass spectrometry (GC–MS) analysis indicated that AtDGAT overexpression caused a drastic elevation in C16 (C16:0 + C16:1) but a slight decline in C18 (C18:0 + C18:1), compared to wild-type N. oceanica, and the variations were further intensified with heat shock. This study offers a valuable and rational strategy of genetic manipulation of TAG content in N. oceanica and facilitates the commercialization of microalgal biofuel. This is also the first successful attempt of overexpression of plant-derived DGAT gene in Nannochloropsis sp., providing novel insights into the genetic engineering of oleaginous microalgae.