Soybean Tissue Culture and Genetic Engineering Center

Biological assessment of the target to increase linolenic acid content in soybean to a level of 15% or higher. The average fatty acid composition of soybean cultivars is: oleic acid (24%), linoleic acid (54%) and linolenic acid (8%). Significant effort has been expended by several groups to increase the oleic acid concentration and decrease the linoleic and linolenic acid content of soybean oil. In the chloroplasts of higher plants oleic acid is converted to linoleic acid by the enzyme oleate desaturase (Fatty Acid Desaturase2 or the FAD2 gene) and linoleic acid is then further desaturated by the enzyme omega-3-desaturase (Fatty Acid Desaturase3 or the FAD3 gene). Thus the effort to increase oleic acid centers around methods to "turn down" efficiency or expression of the FAD2 and FAD3 genes. However, this must be done with caution as this pathway is essential for survival as cell membranes require linoleic and linolenic acid as part of the total fatty acid content. Thus, the objectives are to key on affecting the desaturase proteins during seed fill and not during the vegetative growth phase of plant development. A second objective is to increase the linolenic content of soy oil for other uses, such as for the production of soy-ink. In this manner, the goal is to increase the efficiency, or presence, of the enzyme that converts linoleic acid to linolenic acid (FAD3) during seed fill. A comparison in the level of the FAD3 enzyme in plant species that contain high linolenic acid, such as linseed, has shown that the level of the FAD3 enzyme is at higher levels. Thus, our approach would be to increase the FAD3 protein through a transgenic approach by transforming in the FAD3 gene, expressed under the control of a seed specific promoter, such as the B-conglycinin promoter, to increase the level of the FAD3 enzyme thus increasing the flux from linoleic acid to linolenic acid. Under this approach we could use the soybean FAD3 gene to increase the level of the soybean FAD3 gene product, or use the FAD3 gene from sources that have been shown to contain a level oflinolenic acid, such as the linseed FAD3. The latter approach would be preferable as there would be less possibility that the soybean and linseed genes are identical lessening the chance that gene silencing occurs, that in effect has the opposite effect of that intended. This approach would require isolation and characterization of the linseed FAD3 gene, which is fairly straight-forward using molecular biology approaches, but still has uncertainties as compared to isolating the soybean FAD3 which is already characterized. This target appears to be biologically feasible. The next step is for USB (Mark Winkle and/or others) to determine the accessibility of the FAD2 and FAD3 genes and the economic returns and production gains from higher linolenic acid containing soybean for soy ink and other purposes. USB should also evaluate the IP/FTO issues surrounding the approaches outlined above as DuPont has already done some of this work, and has IP and patent restrictions.