Metabolic engineering of fatty acid biosynthesis in Indian mustard (Brassica juncea) improves nutritional quality of seed oil

The seed oil of Brassica juncea, a widely cultivated oil-seed crop, does not have properly balanced fatty acids required for human nutrition and energy. Moreover, all the cultivars in India produce oil with very high content of erucic acid (C22:1) which is nutritionally undesirable. To divert the carbon flux from erucic acid towards other potentially health beneficial fatty acids, two approaches were implemented. First, a novel FatB thioesterase from Diploknema butyracea was engineered into the B. juncea crop, driven by the napin promoter that is seed-specific. Second, the B. juncea fatty acid elongase was restricted at the genetic level by incorporation of hair-pin RNA known to cause post-transcriptional gene silencing. The fatty acid profile of the mature seed resulted in a 64-82% decrease in erucic acid production. Moreover, the altered seed fatty acid compositions in transgenic lines showed significant increases in the level of C18:1 and C16:0 or C18:0, along with enhancement in the ratio of C18:2/C18:3 and C18:1/C22:1. The reduction of C22 quantitatively accounted for the increase in the pool of C16 and C18 fatty acids in the seed oil. Interestingly, a significant finding was a 4-13% increase in oil content of the different transgenic lines developed by metabolic engineering involving both the plastidial and cytoplasmic enzyme approaches.