Efficient production of transgenic soybean using a co-transformation method

Embryos of Glycine max (L.) Merrill cv. 'Jack' were co-transformed with the hygromycin phosphotransferase (hpt) gene and the jellyfish green fluorescent protein (GFP) gene by microprojectile bombardment. The purpose of this study was to determine the optimum conditions which could achieve the highest co-transformation rate using this method. In the whole process of co-transformation, the screening of transformants was effectively monitored by the expression of GFP. Transformation rates were highest when (1) induced embryos were transferred to a solid medium more than 5 times, (2) only the most highly-proliferated embryos forming globular clusters were bombarded, (3) the helium pressure of rupture disc was 1,100 psi, and (4) the embryogenic tissues 5 days after bombardment were cultured for more than 8 weeks in hygromycin-containing liquid medium for selection. In these conditions, the proportion of clones expressing hygromycin-resistance was 7%, and the proportion of GFP-expressing clones was 18% of them.