Establishment of Agrobacterium-mediated genetic transformation and application of CRISPR/Cas9 gene-editing system to Chinese cabbage (Brassica rapa L. ssp. pekinensis)

Abstract Background: Chinese cabbage, belonging to Brassica rapa species, is an important vegetable in Eastern Asia. It is well known that Chinese cabbage is quite recalcitrant to genetic transformation and the transgenic frequency is generally low. The lack of an efficient and stable genetic transformation system for Chinese cabbage has largely limited related gene functional studies.Results: In this study, we firstly developed a regeneration system for Chinese cabbage by optimizing numerous factors, with 93.50% regeneration rate. Based on this, a simple and efficient Agrobacterium-mediated genetic transformation method was established, without a pre-culture procedure and concentration adjustment of hormone and AgNO3 in co-cultivation and selection media. Using this system, transformants could be obtained within 3.5 to 4.0 months. Average transformation frequency is up to 10.83%. Furthermore, using this transformation system, the CRISPR/Cas9 technology was successfully applied in Chinese cabbage by knocking out a self-incompatibility-related gene SRK. Gene sequencing analysis in the positive transgenic lines revealed various mutations, including deletions, insertions, and substitutions. Conclusion: A simple, stable and efficient genetic transformation method was established for Chinese cabbage and successfully applied to the CRISPR/Cas9 system. The results of this study pave the way for further gene functional studies and genome editing in Chinese cabbage.