The ClTFL1-ClGRFs Module Regulates Lateral Branch Number and Flowering Time via Auxin-Mediated Pathway in Watermelon (Citrullus lanatus)

The early flowering and less lateral branches in watermelon hold significant agricultural value. The synergistic effects of these traits provide an ideal template for watermelon plant architecture improvement. However, the molecular regulatory networks underlying the development of lateral organs (including branches and flowers) in watermelon remain unclear. In this study, we found ClTFL1 knockout lines significantly promote flowering time and inhibit lateral branching and tendril formation, while also leading to a mild apical flower phenotype. These findings indicate that the function of ClTFL1 in watermelon is more extensive than that of its homologous genes in Arabidopsis, rice, and tomato. Through yeast two-hybrid screening, we identified the interacting proteins of ClTFL1, including members of the 14-3-3 family ClGRF8, ClGRF9, and ClGRF12. Bimolecular fluorescence complementation (BiFC) assays further demonstrated ClTFL1 could directly interact with the ClGRF8, ClGRF9, and ClGRF12 protein. The knockout of ClGRF8 and ClGRF12 leads to reduced lateral branches and early flowering. These phenotypes are highly consistent with those of ClTFL1 knockout mutants. Our findings demonstrate the important role of the ClTFL1-ClGRFs module in regulating lateral organ development and flowering time in watermelon, offering important targets for watermelon plant architectural modification and molecular breeding.