Efficient transformation and genome editing of watermelon assisted by genes that encode developmental regulators

The Cucurbitaceae contains multiple species of important food plants. But most of them are difficult to be genetically transformed. Watermelon is one of the most important fruit species of Cucurbitaceae, and it is a model horticulture crops. Its low transgenic efficiency is the major bottleneck in functional genome research and genome editing-based breeding. Here, with the help of genes that encode developmental regulators (DRs), in particular AtGRF5, and an appropriate Agrobacterium strain (GV3101), we have significantly increased the transformation efficiency of watermelon to about 25%, which is a 40-fold increase compared with a traditional vector. AtGRF5-mediated transformation increased the number of transformable watermelon genotypes without causing obvious side effects. Moreover, when applying this strategy to CRISPR/Cas9-mediated genome editing, clpds knockout mutants were generated in the T0 generation. Our results show that AtGRF5 is a powerful and robust tool to effectively create transgenic plants or knockout mutations in watermelon. Similar strategies using DRs might also be able to overcome the transformation barriers in many other Cucurbitaceae species.