Dual Regulatory Roles of SlGAMYB1 in Tomato Development: GA-Dependent and GA-Independent Mechanisms

The R2R3-MYB transcription factor GAMYB plays crucial roles in plant growth and development, but the biological functions of <i>SlGAMYB1</i> in tomato remain poorly understood. Here, we investigated the roles of <i>SlGAMYB1</i> by overexpressing a miR159-resistant version (<i>35S:SlGAMYB1^m</i>) in tomato. Transgenic plants exhibited a dwarf phenotype with reduced internode elongation, which was associated with decreased bioactive gibberellin (GA) levels due to transcriptional repression of <i>SlGA3ox1</i> and activation of <i>SlGA2ox1/2/4/5</i>. Additionally, <i>35S:SlGAMYB1^m</i> altered leaf morphology by inhibiting cell proliferation through downregulation of cell cycle genes, resulting in larger but fewer epidermal cells. Intriguingly, <i>35S:SlGAMYB1^m</i> plants displayed increased floral organ number, a process likely mediated by the upregulation of <i>SlWUS</i> rather than GA signaling. These findings demonstrate that <i>SlGAMYB1</i> regulates diverse aspects of tomato development through both GA-dependent and independent pathways, providing new insights into the functional diversification of <i>GAMYB</i> genes and potential strategies for genetic improvement of tomato architecture and yield.