Screening the rate-limiting genes in the ω6 polyunsaturated fatty acid biosynthesis pathway in Nannochloropsis oceanica

Abstract The enrichment of polyunsaturated fatty acids has made Nannochloropsis sp. a promising candidate for the production of polyunsaturated fatty acids. Although most of the genes involved in polyunsaturated fatty acid biosynthesis have been cloned, the regulatory mechanism at the molecular level has not been elucidated. To target the rate-limiting genes in the ω6 polyunsaturated fatty acid biosynthesis pathway in Nannochloropsis oceanica, we performed the following experiments. The function of the Δ9 fatty acid desaturase gene of N. oceanica was verified in Saccharomyces cerevisiae with a substrate preference for stearic acid. With gas chromatography–mass spectrometry (GC–MS) analysis, the fatty acid profiles in N. oceanica under different stress conditions (high nitrogen, low nitrogen, high temperature, and low temperature) were measured. The results showed that high nitrogen and low temperature stresses played significant roles in promoting polyunsaturated fatty acid biosynthesis. In contrast, low nitrogen and high temperature stresses were beneficial for the accumulation of monounsaturated fatty acids. We further measured the transcriptional abundances of all six genes in the ω6 polyunsaturated fatty acid biosynthesis pathway in N. oceanica and found that the Δ6 fatty acid elongase and the Δ12, Δ5, and Δ17 fatty acid desaturase genes were more sensitive to the stresses set in this study. Pearson correlation analysis showed that the Δ9 fatty acid desaturase was significantly associated with monounsaturated fatty acid biosynthesis, while Δ12, Δ5, and Δ17 fatty acid desaturases were proposed to be the rate-limiting enzymes in polyunsaturated fatty acid biosynthesis. This study helps to thoroughly elucidate the responses of N. oceanica to nitrogen and temperature stresses and optimize cultivation for high yield and quality of polyunsaturated fatty acids. More importantly, the selected rate-limiting genes may benefit further genetic engineering in N. oceanica.