A space-saving visual screening method, Glycine max FAST, for generating transgenic soybean

Establishing homozygous transgenic lines of Glycine max is time-consuming and laborious. To overcome the difficulties, we developed a powerful method for selecting transgenic soybean plants, Fluorescence-Accumulating Seed Technology (GmFAST). GmFAST uses a marker composed of a soybean seed-specific promoter coupled to the OLE1-GFP gene, which encodes a GFP fusion of the oil-body membrane protein OLEOSIN1 of Arabidopsis thaliana. We introduced the marker gene into cotyledonary nodes of G. max Kariyutaka via Agrobacterium-mediated transformation and regenerated heterozygous transgenic plants. OLE1-GFP-expressing soybean seeds can be selected nondestructively with a fluorescence stereomicroscope. Among T₂ seeds, the most strongly fluorescent seeds were homozygous. GmFAST enables to reduce the growing space by one-tenth compared with the conventional method. With this method, we obtained the soybean line that had higher levels of seed pods and oil production. The phenotypes are presumably caused by overexpression of Glyma13g30950, suggesting that Glyma13g30950 regulates seed pod formation in soybean plants. An increase in seed pod number was confirmed in A. thaliana plants that overexpressed the Arabidopsis ortholog of Glyma13g30950, E6L1.Taken together, GmFAST provides a space-saving visual and nondestructive screening method for soybean transformation, thereby increasing the chance of developing useful soybean lines.