Over-Expression of An Isoform of the Delta-12 Fatty Acid Desaturase (FAD2-4) in Transgenic Cotton Plants

Embryogenic cell lines of Gossypium hirsutum L., variety Coker 312 were transformed with a construct designed to over-express one of its own isoforms of fatty acid desaturase - FAD2-4. In cotton, FAD2-4 is part of a multi-gene family and this isoform is expressed mostly throughout plant development, albeit at somewhat lower levels than FAD2-3.  FAD2 introduces the second double bond into fatty acids (converting oleic acid to linoleic acid) and so represents a potential control point for polyunsaturated fatty acid content.  We predict that up-regulating FAD2 activity in cotton plants will increase the proportion of polyunsaturated fatty acids in membranes and may impact tolerance of plants to cooler temperatures, which may be especially beneficial for early planting.   Here we report the generation of transgenic plants and the initial biochemical characterization of these plants. Several independent transgenic cotton plants were produced via Agrobacterium - based transformation. Out of 11 confirmed primary transgenic plants, four plants were fertile and yielded T1 seeds. T1 and T2 seeds were analyzed for total protein and oil content using non-invasive, time-domain (TD) - NMR.  Transgenic seeds were larger in size and mass (10 seed weight).  Further, they showed increased protein content compared to wild type (Coker 312). The fatty acid composition of cotton seed oil is about 26% palmitic acid (16:0), 15% oleic acid (18:1) and 55% linoleic acid (18:2), and this seed fatty acid composition was unchanged in transgenics. On the other hand, the fatty acid composition of young leaves from some of the T1 and T2 plants showed significant differences in polyunsaturated fatty acid composition compared to wild type.   Assays for tolerance of FAD2-4 overexpressing seeds and seedlings to cool temperatures are underway.