Identification of bifunctional Δ12/ω3 fatty acid desaturases for improving the ratio of ω3 to ω6 fatty acids in microbes and plants

摘要

We report the identification of bifunctional Δ12/ω3 desaturases from Fusarium moniliforme, Fusarium graminearum, and Magnaporthe grisea. The bifunctional activity of these desaturases distinguishes them from all known Δ12 or ω3 fatty acid desaturases. The ω3 desaturase activity of these enzymes also shows a broad ω6 fatty acid substrate specificity by their ability to convert linoleic acid (LA), γ-linolenic acid, di-homo-γ-linolenic acid, and arachidonic acid to the ω3 fatty acids, α-linolenic acid (ALA), stearidonic acid, eicosatetraenoic acid, and eicosapentaenoic acid (EPA), respectively. Phylogenetic analysis suggests that ω3 desaturases arose by independent gene duplication events from a Δ12 desaturase ancestor. Expression of F. moniliforme Δ12/ω3 desaturase resulted in high ALA content in both Yarrowia lipolytica, an oleaginous yeast naturally deficient in ω3 desaturation, and soybean. In soybean, seed-specific expression resulted in 70.9 weight percent of total fatty acid (%TFA) ALA in a transformed seed compared with 10.9%TFA in a null segregant seed and 53.2%TFA in the current best source of ALA, linseed oil. The ALA/LA ratio in transformed seed was 22.3, a 110- and 7-fold improvement over the null segregant seed and linseed oil, respectively. Thus, these desaturases have potential for producing nutritionally desirable ω3 long-chain polyunsaturated fatty acids, such as EPA, with a significantly improved ratio of ω3/ω6 long-chain polyunsaturated fatty acids in both oilseeds and oleaginous microbes.