Sonication-assisted Agrobacterium-mediated transformation of soybean [Glycine max (L.) Merrill] embryogenic...

Successful transformation of plant tissue using Agrobacterium relies on several factors including bacterial infection, host recognition, and transformation competency of the target tissue. Although soybean [Glycine max (L.) Merrill] embryogenic suspension cultures have been transformed via particle bombardment, Agrobacterium-mediated transformation of this tissue has not been demonstrated. We report here transformation of embryogenic suspension cultures of soybean using "Sonication-Assisted Agrobacterium-mediated Transformation" (SAAT). For SAAT of suspension culture tissue, 10-20 embryogenic clumps (2-4 mm in diameter) were inoculated with 1 ml of diluted (OD_600nm 0.1-0.5) log phase Agrobacterium and sonicated for 0-300 s. After 2 days of co-culture in a maintenance medium containing 100 µM acetosyringone, the medium was removed and replaced with fresh maintenance medium containing 400 mg/l Timentin^®. Two weeks after SAAT, the tissue was placed in maintenance medium containing 20 mg/l hygromycin and 400 mg/l Timentin^®, and the medium was replenished every week thereafter. Transgenic clones were observed and isolated 6-8 weeks following SAAT. When SAAT was not used, hygromycin-resistant clones were not obtained. Southern hybridization analyses of transformed embryogenic tissue confirmed T-DNA integration.