Development and identification of glyphosate-tolerant transgenic soybean viadirect selection with glyphosate

Glyphosate-tolerant soybean is the most widely planted genetically modified crop worldwide. However, soybean remains recalcitrant to routine transformation because of the low infection efficiency of Agrobacteriumto soybean and lack of useful selectable markers. In this study, several Agrobacteriumstrains and cell densities were compared by transient expression of the GUSgene. The results showed that Agrobacteriumstrain Ag10 at cell densities of OD600of 0.6–0.9 yielded the highest infection efficiency in Agrobacterium-mediated soybean cotyledonary node transformation system. Meanwhile, a simple and rapid method was developed for identification of glyphosate tolerance in putative T0transgenic plants, consisting of spotting plantlets with 1 µL Roundup®. The whole cycle of genetic transformation could be shortened to about 3 mon by highly efficient selection with glyphosate during the transformation process and application of the spot assay in putative T0transgenic plantlets. The transformation frequency ranged from 2.9 to 5.6%. This study provides an improved protocol for development and identification of glyphosate-tolerant transgenic soybeans.