Leaf primordia margins maintain a transient window of morphogenetic activity, which determines leaf pattern variability. However, the regulatory mechanism for maintaining leaf morphogenetic capacity is still poorly understood. Su et al. (on pp. 535-549) identified a tomato BRI1-EMS-SUPPRESSOR 1 (BES1) transcription factor, SlBES1.8, which can promote the simplification of leaf patterning; SlBES1.8 directly represses the expression of two gibberellin (GA) deactivated genes SlGA2ox2 and SlGA2ox6, which results in the accumulation of endogenous bioactive GA and the degradation of a negative regulator of GA signaling, SlDELLA. Moreover, SlDELLA physically interacts with SlBES1.8 to further inhibit its transcriptional regulation activity by abolishing SlBES1.8-DNA binding. These results provide new insight into the crosstalk between BES1 transcription factors and GA levels or signaling in regulating leaf morphogenesis.