| Summary: | <p>Abstract</p> <p>Background</p> <p>The application and nutritional value of vegetable oil is highly dependent on its fatty acid composition, especially the relative proportion of its two major fatty acids, i.e oleic acid and linoleic acid. Microsomal oleoyl phosphatidylcholine desaturase encoded by <it>FAD2</it> gene is known to introduce a double bond at the Δ12 position of an oleic acid on phosphatidylcholine and convert it to linoleic acid. The known plant FAD2 enzymes are encoded by small gene families consisting of 1-4 members. In addition to the classic oleate Δ12-desaturation activity, functional variants of FAD2 that are capable of undertaking additional or alternative acyl modifications have also been reported in a limited number of plant species. In this study, our objective was to identify <it>FAD2</it> genes from safflower and analyse their differential expression profile and potentially diversified functionality.</p> <p>Results</p> <p>We report here the characterization and functional expression of an exceptionally large <it>FAD2</it> gene family from safflower, and the temporal and spatial expression profiles of these genes as revealed through Real-Time quantitative PCR. The diversified functionalities of some of the safflower <it>FAD2</it> gene family members were demonstrated by ectopic expression in yeast and transient expression in <it>Nicotiana benthamiana</it> leaves. <it>CtFAD2-1</it> and <it>CtFAD2-10</it> were demonstrated to be oleate desaturases specifically expressed in developing seeds and flower head, respectively, while <it>CtFAD2-2</it> appears to have relatively low oleate desaturation activity throughout the plant. <it>CtFAD2-5</it> and <it>CtFAD2-8</it> are specifically expressed in root tissues, while <it>CtFAD2-3, 4, 6, 7</it> are mostly expressed in the cotyledons and hypocotyls in young safflower seedlings. <it>CtFAD2-9</it> was found to encode a novel desaturase operating on C16:1 substrate. CtFAD2-11 is a tri-functional enzyme able to introduce a carbon double bond in either <it>cis</it> or <it>trans</it> configuration, or a carbon triple (acetylenic) bond at the Δ12 position.</p> <p>Conclusions</p> <p>In this study, we isolated an unusually large <it>FAD2</it> gene family with 11 members from safflower. The seed expressed <it>FAD2</it> oleate Δ12 desaturase genes identified in this study will provide candidate targets to manipulate the oleic acid level in safflower seed oil. Further, the divergent FAD2 enzymes with novel functionality could be used to produce rare fatty acids, such as crepenynic acid, in genetically engineered crop plants that are precursors for economically important phytoalexins and oleochemical products.</p>
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