Agrobacterium-mediated transformation system for large-scale producion of transgenic Chinese cabbage (Brassica rapa L. ssp pekinensis) plants for insertional mutagenesis

In order to better utilize insertional mutagenesis and functional genomics in Chinese cabbage, we have developed an improved transformation system that more efficiently produces a large number of transgenic plants. Hypocotyl explants were inoculated with Agrobacterium tumefaciens LBA4404. This strain harbors tagging vector pRCV2, which contains a hygromycin-resistance gene, an ampicillin resistance gene, and a bacterial replication origin within the TDNA. Transformation efficiency was highest when the explants were first co-cultivated for 3 d in a medium supplemented with 5 mg L-1 acetosyringone, then transferred to a 0.8% agar selection medium containing 10 mg L-1 hygromycin. In addition, maintaining a low pH in the co-cultivation medium was critical to enhancing transformation frequency. A total of 3369 transgenic plants were obtained, with efficiencies ranging from 2.89% to 5.00%. Southern blot analysis and T, progeny tests from 120 transgenic plants confirmed that the transgenes were stably inherited to the next generation. We also conducted plasmid rescue and inverse PCR with some transformants, based on their phenotype, to demonstrate the applicability of T-DNA tagging in Chinese cabbage. The tagged sequences were then analyzed.