Synthetic Design of New Plant Oil Traits for Oilseed Crops As Sustainable and High-Quality Feedstock

Using soy products as fish food ingredients is sustainable and viable for fish aquaculture. However, the current soy-based feed lacks EPA/DHA omega-3 fatty acids and oil-based feed components, like astaxanthin, needed to obtain the pink-color of some fish meat. Because of these deficiencies, soy-based aquaculture feed currently requires supplementation with fish oil and high-priced astaxanthin, particularly for farm-raised fishes like salmon and trout. In addition, oils with high very-long-chain polyunsaturated fatty acids content are easily oxidized, which limits the shelf life of fish due to the development of off-flavors and odors. For that reason, a high vitamin E antioxidant trait is needed to provide oxidative stability. Conventional plant breeding and biotechnology approaches typically target only one or a small number of traits at a time. In contrast, the emerging discipline of synthetic biology offers tools for making step changes in crop improvement by enabling integration of many trait genes into the crop genome in a single genetic transformation. The goal of our research is the stacking of multiple oil traits: EPA/DHA, astaxanthin, and vitamin E, to obtain a single soybean line with optimized aquaculture feed value. To produce EPA, five transgenes including desaturase and elongase from diverse organisms were synthesized with barley HGGT, which is involved in the production of vitamin E. For astaxanthin production, β-ring oxygenase and astaxanthin synthase from Adonis aestivalis were used. An 8-transgene expression vector with seed-specific promoters was constructed and transformed into soybean. T3 seeds successfully produce EPA, vitamin E, and astaxanthin. To evaluate the upper limit of transgene numbers that can be introduced into plant from one construct, we also constructed ten modules with multi trait genes to generate improved sustainability and biofuel and industrial quality traits. These trait targets include genes for heat tolerance, seed size, oil content, oil quality, and protein quality.