Research Highlights

High-Protein Content Soybean Genetics Research

By Laura Temple

Soybeans deliver the highest level of crude protein among plant-based protein sources. That’s why soybean meal has become a major feedstock for poultry, swine and other livestock and aquaculture industries. In fact, more than 60 percent of total soybean value comes from its use as a protein source in feed.

“Soybean meal should contain at least 47.5 percent protein, which means that soybeans with a lower protein content are less valuable to processors and growers,” explains Dr. Saghai Maroof, a faculty member in the School of Plant and Environmental Sciences at Virginia Tech University. “Soybeans have a negative correlation between protein content and both yield and oil content. Due to decades of breeding for increased yield, soybean protein content has declined over time.”

In response, Maroof initiated research funded in part by the Virginia Soybean Board to identify high-protein genes in soybeans and associated DNA markers to facilitate the development of high-protein soybean varieties.

“Protein content is a complex trait controlled by multiple genes in soybeans,” he says. “It’s also drastically influenced by environmental conditions. Therefore, increasing soybean protein content without reducing yield and oil content is a breeding challenge.”

To tackle this challenge, Maroof and his team are taking two genetic approaches. Regardless of approach, the goal of this research is to identify regions within the 20 chromosome pairs in soybeans that contain genes controlling protein content. Then, developing DNA markers for genes tied to that high-protein content will provide practical, valuable tools for soybean breeders. 

“With DNA markers, breeders will not always have to measure protein content of soybean cultivars,” Maroof explains. “They can use the markers to accelerate the development of new high-protein, good-yielding varieties.”

High protein inheritance study

The genetic material for an inheritance study came from crosses between soybean lines with the lowest and highest protein contents in 2010. From those crosses, segregating populations has been advanced to the eighth generation to ensure genetic uniformity. 

Chromosomal mapping of each individual in the population, coupled with tissue and dry matter analysis from field trials, will segregate low- and high-protein content genes. The maps will support quantitative trait locus (QTL) identification, showing the regions on chromosomes where genes influence protein content. 

“Reductions in genome sequencing cost enable us to construct detailed chromosomal maps,” Maroof explains. “Combined with protein data from field trials, we have already identified several regions controlling seed protein content. We are now developing easy-to-use DNA markers suitable for marker-assisted selection in soybean breeding.”

Genome-wide association analysis

The second approach relies on the USDA germplasm collection, which contains countless soybean plant introductions. 

“Prior United Soybean Board (USB) investment in the soybean scientific community to fingerprint the soybean plant introductions facilitates this approach,” Maroof says. “The protein and marker data of the plant introduction lines in our study will be combined and subjected to association analysis across the soybean genome.”

The association analysis will further identify high-protein germplasm, protein-related genes and QTLs associated with protein content. Maroof expects these approaches to eventually result in soybean breeding lines with high-protein content and strong yields.

“We are developing tools for breeders that can improve soybean protein content for domestic and export markets,” he says. “Higher protein content will improve profitability for U.S. soybean producers. Improving soybean quality without reducing yield will help U.S. soybeans compete globally.”

Published: Jan 4, 2021