Improved soybean transformation for efficient and high throughput transgenic production

Although genetic transformation of soybean dates back to over two decades, the process remains inefficient. Here, we report the development of an organogenesis-based transformation method of soybean that resulted in an average transformation frequency of 18.7%. This improved method resorts to Agrobacterium-mediated transformation of the split-seed explant with an attached partial embryonic axis obtained from an imbibed seed. In addition to the split-seed explant, Agrobacterium strain and preparation were shown to be important for improved transformation. Transformation with Agrobacterium tumefaciens EHA105 generated higher transformation frequencies and number of low copy events compared to the strain EHA101. In this system, phosphinothricin acetyl transferase conferring tolerance to glufosinate was successfully employed for efficiently producing transgenic events. Around 48% of the T₁ progeny was demonstrated to be heritable based on molecular analysis and screening with the herbicide Liberty^®. This method was shown to be applicable to different genotypes and a few elite lines showed high transformation frequencies. This split-seed system with an attached partial embryonic axis serves not only as an efficient means for high throughput transgenic production for basic research studies but also for the commercial development of transgenic soybean products.