Biotechnology of α-linolenic acid in oilseed rape (Brassica napus) using FAD2 and FAD3 from chia (Salvia hispanica)

α-Linolenic acid (ALA, 18:3Δ9,12,15) is an essential fatty acid for human, since it is the precursor for the biosynthesis of omega-3 long-chain polyunsaturated fatty acids (LC-PUFA). Modern people generally suffer from deficiency of ALA, since most staple food oils are low or lack in ALA content. Biotechnological enrichment of ALA in staple oil crops is a promising strategy. Among known oil crops, chia (Salvia hispanica) has the highest ALA content in its seed oil. In this study, the FAD2 and FAD3 genes from chia were engineered into a staple oil crop, oilseed rape (Brassica napus), via Agrobaterium tumefaciens-mediated transformation of their LP4-2A fusion gene construct driven by the seed-specific promoter PNapA. In seeds of T0, T1 and T2 lines, the average ALA contents were 20.86, 23.54 and 24.92%, which were 2.21, 2.68 and 3.03 folds of the non-transformed controls (9.42, 8.78 and 8.22%), respectively. The highest ALA levels of seeds of T0, T1 and T2 plants, were 38.41, 35.98 and 39.19% respectively, which were 4.10-4.77 folds of the respective controls. FA-pathway enzyme genes BnACCD, BnFATA, BnSAD, BnSCD, BnDGAT1, BnDGAT2 and BnDGAT3 as well as positive regulatory genes BnWRI1, BnLEC1, BnL1L, BnLEC2, BnABI3, BnbZIP67 and BnMYB96 were all significantly up-regulated. In contrast, BnTT1, BnTT2, BnTT8, BnTT16, BnTTG1 and BnTTG2, encoding negative regulators of oil accumulation but positive regulators of secondary metabolism, were all significantly down-regulated. These mean that foreign ShFAD2-ShFAD3 fusion gene directly and indirectly remodeled both positive and negative loci of the whole FA-related network in transgenic B. napus seeds.