Association of a Soybean Raffinose Synthase Gene with Low Raffinose and Stachyose Seed Phenotype

Oligosaccharides are an important component of soybean [Glycine max (L.) Merr.] meal in terms of metabolizable energy for monogastric animals. Sucrose, raffinose, and stachyose are the three main oligosaccharides present in soybean meal. Of the three, only sucrose is nutritionally useful. When raffinose and stachyose are fermented by microbes present in the gut, the results are flatulence and discomfort, which ultimately lead to poor weight gain. The long term objective of this research is ultimately to increase the nutritional value of soybean meal by elevating the metabolizable energy at the expense of raffinose and stachyose through the manipulation of soybean raffinose synthase, the key enzyme for raffinose and stachyose biosynthesis. The objectives of this work were to develop molecular genetic information about soybean raffinose synthases and to evaluate the candidate raffinose synthase genes in a soybean germplasm accession (PI 200508) that contains low levels of raffinose and stachyose. Our results indicate the soybean genome contains at least two expressed genes similar to other characterized raffinose synthases. A novel allele of one of these putative soybean raffinose synthase genes was discovered from the PI 200508 that completely associates with the low raffinose and stachyose phenotype. Molecular marker assays specific for the PI 200508 allele were developed to allow direct selection for the low raffinose and low stachyose phenotype.