Highly efficient, genotype‐independent transformation and gene editing in watermelon (Citrullus lanatus) using a chimeric ClGRF4‐GIF1 gene

Summary Efficient genetic transformation has the potential to advance research and breeding in watermelon (Citrullus lanatus), but regeneration from tissue culture remains challenging. Previous work showed that expressing a fusion of two interacting transcription factors, GROWTH‐REGULATING FACTOR4 (GRF4) and GRF‐INTERACTING FACTOR1 (GIF1), improved regeneration in wheat (Triticum aestivum). By overexpressing a chimeric fusion of ClGRF4 and ClGIF1, we achieved highly efficient transformation in watermelon. Mutating the mi396 microRNA target site in ClGRF further boosted the transformation efficiency up to 67.27% in a genotype‐independent manner. ClGRF4‐GIF1 can also be combined with clustered regularly interspaced palindromic repeats (CRISPR)/CRISPR‐associated protein 9 (Cas9) genome editing tools to achieve highly efficient gene editing in watermelon, which we used to successfully create diploid seedless watermelon. This research thus puts forward a powerful transformation tool for future watermelon research and breeding. A highly efficient genetic transformation system in watermelon using an endogenous chimeric ClGRF4‐GIF1 gene achieved genotype‐independent transformation, even with previous non‐transformable materials. ClGRF4‐GIF1 can be combined with CRISPR/Cas9 to achieve highly efficient gene editing in watermelon and will greatly benefit future watermelon research and breeding.