The role of Δ6-desaturase acyl-carrier specificity in the efficient synthesis of long-chain polyunsaturated fatty acids in transgenic plants

The role of acyl-CoA-dependent Delta 6-desaturation in the heterologous synthesis of omega-3 long-chain polyunsaturated fatty acids was systematically evaluated in transgenic yeast and Arabidopsis thaliana. The acyl-CoA Delta 6-desaturase from the picoalga Ostreococcus tauri and orthologous activities from mouse (Mus musculus) and salmon (Salmo salar) were shown to generate substantial levels of Delta 6-desaturated acyl-CoAs, in contrast to the phospholipid-dependent Delta 6-desaturases from higher plants that failed to modify this metabolic pool. Transgenic plants expressing the acyl-CoA Delta 6-desaturases from either O.tauri or salmon, in conjunction with the two additional activities required for the synthesis of C20 polyunsaturated fatty acids, contained higher levels of eicosapentaenoic acid compared with plants expressing the borage phospholipid-dependent Delta 6-desaturase. The use of acyl-CoA-dependent Delta 6-desaturases almost completely abolished the accumulation of unwanted biosynthetic intermediates such as gamma-linolenic acid in total seed lipids. Expression of acyl-CoA Delta 6-desaturases resulted in increased distribution of long-chain polyunsaturated fatty acids in the polar lipids of transgenic plants, reflecting the larger substrate pool available for acylation by enzymes of the Kennedy pathway. Expression of the O.tauri Delta 6-desaturase in transgenic Camelina sativa plants also resulted in the accumulation of high levels of Delta 6-desaturated fatty acids. This study provides evidence for the efficacy of using acyl-CoA-dependent Delta 6-desaturases in the efficient metabolic engineering of transgenic plants with high value traits such as the synthesis of omega-3 LC-PUFAs.