An attempt to synthesize nervonic acid in rapeseed leaves by metabolic engineering

Nervonic acid (NA), a very long-chain monounsaturated fatty acid, with high value in brain disease prevention and improvement, many studies revealed it could be synthesized in crop seeds via genetic engineering. In recent years, vegetative tissues such as leaves have been proposed as a novel platform for producing triacylglycerol (TAG) and achieving significant results, but the potential for producing NA has not been explored. In this study, three genes, CgKCS from (正体) Cardamine graeca, SLC1-1 from Saccharomyces cerevisiae, and DGAT1 from Arabidopsis thaliana, were selected and under the regulation of the green organizations-specific promoter Rubisco to form multi-gene vector and transformed four varieties rapeseed with different fatty acid profile to explore the potential of NA production in leaves. Those genes have been respectively reported to increase NA production, promote Fatty acids (FAs) combining to the sn-2 of TAG, and improve crop oil content of plant seeds. In this study, NA was not detected in all four varieties of transgenic rapeseed leaves at vegetative, flowering, and seed setting three development stages. Analysis of fatty acid components results shown that linolenic acid (C18:3) is the main fatty acid in leaves, but the available substrates for synthesizing NA are monounsaturated fatty acids, such as C18:1, C20:1, and C22:1, so lacking of monounsaturated fatty acids maybe is the main limiting factor for the production NA in transgenic rapeseed leaves. And then, we further analyzed the feasible strategies to promote NA and other very long-chain fatty acids synthesis, assembly and accumulation. Together, our results provide a clear profile of the fatty acid composition of rapeseed leaves and although it failed to synthesize NA, it also provides referable hints for the production of NA from rapeseed leaves via metabolic engineering.