DEVELOPMENTAL AND GROWTH TEMPERATURE REGULATION OF 2 DIFFERENT MICROSOMAL OMEGA-6 DESATURASE GENES IN SOYBEANS

The polyunsaturated fatty acid content is one of the major factors inf luencing the quality of vegetable oils. Edible oils rich in monounsatu rated fatty acid provide improved oil stability, flavor, and nutrition for human and animal consumption. In plants, the microsomal omega-6 d esaturase-catalyzed pathway is the primary route of production of poly unsaturated lipids. We report the isolation of two different cDNA sequ ences, FAD2-1 and FAD2-2, encoding microsomal omega-6 desaturase in so ybeans and the characterization of their developmental and temperature regulation. The FAD2-1 gene is strongly expressed in developing seeds , whereas the FAD2-2 gene is constitutively expressed in both vegetati ve tissues and developing seeds. Thus, the FAD2-2 gene-encoded omega-6 desaturase appears to be responsible for production of polyunsaturate d fatty acids within membrane lipids in both vegetative tissues and de veloping seeds. The seed-specifically expressed FAD2-1 gene is likely to play a major role in controlling conversion of oleic acid to linole ic acid within storage lipids during seed development. In both soybean seed and leaf tissues, linoleic acid and linolenic acid levels gradua lly increase as temperature decreases. However, the levels of transcri pts for FAD2-1, FAD2-2, and the plastidial omega-6 desaturase gene (FA D 6) do not increase at low temperature. These results suggest that th e elevated polyunsaturated fatty acid levels in developing soybean see ds grown at low temperature are not due to the enhanced expression of omega-6 desaturase genes.