Research Highlights

Development of High-Yielding, High-Protein Germplasm by Enhancing Nitrogen Acquisition and Its Transport to Seed

By Felix Fritschi, University of Missouri

Soybean seeds are an important source of protein. However, although the protein concentration in soybean seeds is relatively high when compared to other legumes, the steady decline in protein content over recent years has made the production of high-protein seed meal from soybeans increasingly challenging for processors. In light of this decline, a research focus on seed protein quantity and quality is critical. This research will ensure that processors can continue to produce high-quality soybean meal and not only maintain, but enhance, the competitive edge of U.S. soybean meal in the global marketplace.

Soybean’s relatively high seed protein content and its ability to access nitrogen from the atmosphere (also known as “nitrogen fixation”) have resulted in its development as a very important crop in the United States. In soybean, nitrogen uptake and assimilation take place in different tissues than nitrogen utilization. Following its acquisition from the soil or atmosphere, nitrogen is reduced into ureides and amino acids in roots or nodules, and these organic nitrogen-containing compounds are exported to a variety of sink tissues (such as vegetative tissues and seeds) for plant growth and yield formation.

The focus of this research project is to understand and manipulate both uptake and export of organic nitrogen and sulfur throughout the soybean plant, with the goal of understanding how transport proteins function in the delivery of nitrogen metabolites to seeds, and on their role in seed development. This includes transport of nitrogen and sulfur from source organs (i.e., nodules and leaves), import of amino acids into seeds, and increasing both the number of seeds and the protein levels in those seeds. In 2019, this project was funded by the United Soybean Board for $152,358 to develop soybean lines with enhanced nitrogen acquisition properties and nitrogen and sulfur allocation, and therefore increased soybean seed and protein yield as well as seed nutritional quality.

To date, soybean plants have been grown that overexpress a transporter gene for the products of nitrogen fixation (ureides) under field conditions, and these plants were used to assess impacts on both yield and soybean seed protein concentration. In the first year, one of the transgenic lines produced seeds with an increased protein concentration, and a second year of field studies was conducted. Seed analyses from the second year are ongoing.

In addition, a number of transgenic soybean plants overexpressing amino acid transporters in the phloem and seed cotyledons have been developed, including transgenic lines which overexpress a single transporter or contain a combination of two transporters. These transgenic plants are currently being advanced to the next generation, and the impact of overexpression on soybean protein composition and concentration, as well as yield, will be determined.

Enhancing soybean nitrogen acquisition, nitrogen allocation to seeds, and seed sulfur-containing amino acid concentrations will in turn increase soybean nutritional quality and thus the competitiveness of U.S. soybean. If verified under field conditions, the soybean lines generated by this project may translate into improved seed varieties, bring added value to soybean meal and subsequently even enhance demand. The continued investment into this research will ultimately result in improved soybean cultivars that will benefit soybean producers and their customers worldwide.

Published: May 7, 2020