Suppression of SDP1 improves soybean seed composition by increasing oil and reducing undigestible oligosaccharides

Authors: AZNAR-MORENO, JOSE - Kansas State University; MUKHERJEE, THIYA - Danforth Plant Science Center; Morley, Stewart; DURESSA, DECHASSA - Kansas State University; KAMBHAMPATI, SHRIKAAR - Danforth Plant Science Center; Chu, Kevin; KOLEY, SOMNATH - Danforth Plant Science Center; Allen, Douglas - Doug; DURRETT, TIMOTHY - Kansas State University

Submitted to: Plant Biotechnology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2022
Publication Date: 3/23/2022
Citation: Aznar-Moreno, J.A., Mukherjee, T., Morley, S.A., Duressa, D., Kambhampati, S., Chu, K.L., Koley, S., Allen, D.K., Durrett, T.P. 2022. Suppression of SDP1 improves soybean seed composition by increasing oil and reducing undigestible oligosaccharides. Plant Biotechnology Journal. 13. Article 863254. https://doi.org/10.3389/fpls.2022.863254.
DOI: https://doi.org/10.3389/fpls.2022.863254

Interpretive Summary: Soybeans are an important source of vegetable oil, protein-enriched meal that is a primary source of nutrition in animal diets, and are the main feed stock used for biofuels and many renewable plastics, polymers, adhesives and detergents. Increasing the amount of oil in soybeans usually comes at the expense of a reduction in the amount of protein. If soybean plants could be altered to make more oil without reductions in protein, the seeds could contribute to additional needs in society in a sustainable way, making them more valuable which would generate increased profits for farmers. We engineered soybeans to accumulate more oil by reducing the expression of a gene that breaks down oil and leads to the production of several lesser valued carbohydrates. We characterized the altered seeds by measuring biomass contents, using gene expression and assaying germination. Our results indicate increased oil levels, without a penalty in protein levels. Further, the seeds were bigger resulting in more seed biomass per plant and indicate that the production of more oil may not have a yield penalty. This work provides an avenue to producing value-added soybeans that can meeting increasing societal demands.

Technical Abstract: In developing soybean seeds, carbon is partitioned between oil, protein and carbohydrates. Here, we demonstrate that suppression of lipase-mediated turnover of triacylglycerols (TAG) during late seed development increases fatty acid content and decreases the presence of undigestible oligosaccharides. During late stages of embryo development, the fatty acid content of soybean seed decreases while the levels of the oligosaccharides raffinose and stachyose increase. Three soybean genes orthologous to the Arabidopsis lipase gene SUGAR-DEPENDENT1 (SDP1) are upregulated at this time. Suppression of these genes resulted in higher oil levels, with lipid levels in the best lines exceeding 24% of seed weight. In addition, lipase-suppressed lines produced larger seeds compared to wild-type plants, resulting in increases of over 20% in total lipid per seed. Levels of raffinose and stachyose were lower in the transgenic lines, with average reductions of 15% in total raffinose family oligosaccharides observed. Despite the increase in oil, protein content was not negatively impacted and trended higher in the transgenic lines. These results are consistent with a role for SDP1 in turning over TAG to supply carbon for other needs, including the synthesis of oligosaccharides, and offer new strategies to further improve the composition of soybean seeds.