Optimization of particle bombardment conditions by monitoring of transient sGFP(S65T) expression in transformed soybean

In an attempt to increase the efficiency of soybean transformation by particle bombardment, we examined the effects of bombardment parameters such as gold particle size, target distance, acceleration pressure, amount of DNA per bombardment, and number of bombardments. Transgene delivery to embryogenic tissue grown in suspension culture was evaluated by monitoring the transient expression of a gene for a modified form of jellyfish green fluorescent protein [sGFP(S65T)]. Optimal transient expression of sGFP(S65T) was obtained when the tissue was bombarded twice at an acceleration pressure of 7.6 MPa (1,100 psi) and a distance of 6 cm with gold particles that were 0.6 mu m in diameter and coated with 0.8 mu g of DNA. Application of these optimized conditions proved effective for the generation of stable transgenic soybean plants. Stable transgene integration in the transformants was confirmed by Southern blot analysis. The average transformation efficiency achieved with the optimized protocol was siginificantly higher than that with the conventional protocol.