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

Abstract

Soybean is an important crop plant for food and biofuel production, and there have been considerable efforts to develop transgenic soybean lines with higher seed oil contents and/or seed yields. However, the process of screening transgenic lines is laborious and requires a large amount of space. Here, we describe a powerful screening method, Glycine max Fluorescence-Accumulating Seed Technology (GmFAST), which is based on a seed-specific fluorescent marker. The marker is composed of a soybean seed-specific promoter coupled to the OLE1-GFP gene, which encodes GFP fused to 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 using a fluorescence stereomicroscope. Among T2 seeds, the most strongly fluorescent seeds were homozygous. GmFAST uses one-tenth of the growing space required for the conventional method. This space-saving method will contribute to facilitating transformation of soybean. OLE1-GFP was localized specifically to oil bodies in the cotyledon cells of seeds, but it did not affect oil content per seed, the size and density of the oil bodies, or oil composition. One of the homozygous lines (line #8) showed a 44% increase in the seed pod number, which resulted in 41% and 30% increases in seed yield and total oil production, respectively, compared with the wild type. In line #8, OLE1-GFP was inserted into the intron of Glyma13g30950, causing its overexpression. An increase in seed pod number was confirmed in Arabidopsis thaliana plants that overexpressed the Arabidopsis ortholog of Glyma13g30950, E6L1. These results suggest that line #8 is a valuable resource for agricultural and industrial applications. Taken together, GmFAST provides a space-saving visual and non-destructive screening method for soybean transformation, thereby increasing the chance of developing useful soybean lines.