Genome-Wide Identification of GW5-LIKE Family Revealed the Function of ClGL1 Involved in Fruit and Seed Shape by Mediating Brassinosteroid Signaling in Watermelon

The regulatory mechanism of brassinolide (BR) signaling in cucurbitaceae crops remains incompletely understood. Previous research demonstrated that the rice genes GW5 and GW5L modulate seed morphology via the BR pathway. However, the conservation of their orthologs in watermelon and their evolutionary trajectory are yet to be elucidated. In this study utilizing the watermelon 97103v2 genome, we identified 15 GW5-LIKE genes. Through structure, phylogenetic tree construction, collinearity, promoter and spatiotemporal expression analysis, we determined that ClGL1 to ClGL3 are the most closely related to GW5 and GW5L. Subsequently, two crucial materials were acquired: the inbred line Jing L6M harboring the homozygous mutant Clgl1, and the near-isogenic line Changhong, a Jing L6M backcross containing the wild-type allele ClGL1. Apart from the disparity in fruit morphology, a clear difference in seed shape was observed between the two. Furthermore, exogenous BR treatment demonstrated that ClGL1 positively regulated the BR signal, aligning with the positive impact of GW5 and GW5L. In conclusion, ClGL1 modulates the morphology of watermelon fruit and seed by enhancing BR signaling, which provides a key gene and theoretical basis for BR signaling evolution and molecular design breeding in Cucurbitaceae.