Abstract :
We report the identification of bifunctional [DELTA]12/[omega]3 desaturases from Fusarium moniliforme, Fusarium graminearum, and Magnaporthe grisea. The bifunctional activity of these desaturases distinguishes them from all known [delta]12 or [omega]3 fatty acid desaturases. The [omega]3 desaturase activity of these enzymes also shows a broad [omega]6 fatty acid substrate specificity by their ability to convert linoleic acid (LA), [gamma]-linolenic acid, di-homo-[gamma]-linolenic acid, and arachidonic acid to the [omega]3 fatty acids, [alpha]-linolenic acid (ALA), stearidonic acid, eicosatetraenoic acid, and eicosapentaenoic acid (EPA), respectively. Phylogenetic analysis suggests that [omega]3 desaturases arose by independent gene duplication events from a [DELTA]12 desaturase ancestor. Expression of F. moniliforme [DELTA]12/[omega]3 desaturase resulted in high ALA content in both Yarrowia lipolytica, an oleaginous yeast naturally deficient in [omega]3 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 [omega]3 long-chain polyunsaturated fatty acids, such as EPA, with a significantly improved ratio of [omega]3/[omega]6 long-chain polyunsaturated fatty acids in both oilseeds and oleaginous microbes. polyunsaturated fatty acids | Yarrowia | soybean