By Lauren Quinn
Soybeans outmatch all other legumes as the protein powerhouses of the plant kingdom, providing a key protein source for humans and livestock around the world. And now, after 30 years, University of Illinois scientists have identified the gene with the largest impact on seed protein in soybean.
"Soybeans are around 40% protein, and this gene increases that about 2%. It doesn't sound like a lot, but compared to any other seed-protein gene that's been mapped for soybean, it's at least double," says Brian Diers, the Charles Adlai Ewing Chair of Soybean Genetics and Breeding in the Department of Crop Sciences and co-author of the study in The Plant Journal.
Co-author Matt Hudson, Professor of Bioinformatics in Crop Sciences, adds, "If we could put the high protein form of the gene into commercially grown varieties, we would be looking at a significant increase in protein for livestock and humans worldwide as even a single percentage point increase in protein concentration would represent millions of tons of protein. That's quite significant."
In 1992, then-graduate-student Diers published the first seed protein map for soybean. Although he identified the region of the genome where the gene might be located, it took three decades, many technological advances, and the publication of two soybean genomes to nail down the specific gene: Glyma.20G85100, a gene without a known function but closely related to "clock and circadian timing" genes.
"It's satisfying to make the journey from being an eager young grad student, all excited about this finding, to finally determining what the gene is," Diers says. "But if I go back to myself 30 years ago, I could never have imagined it would have taken this long. But better late than never."
Pinpointing a gene like this is complicated because it's one of many quantitative trait loci: Locations within the genome contributing to continuous traits like plant height, yield, or in this case, protein content.
Researchers have to grow the plants, measure protein content, and then drill down into the genome to find correlated genetic differences among plants with different amounts of protein. Those genetic differences might not be detectible, or they might only be traceable to large sections of the genome.
Diers says he originally mapped the gene to a section of a chromosome several million base pairs of DNA long. But by testing generation after generation of plants carrying the gene within smaller genetic regions, he slowly narrowed it down.
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