Manipulation of the PtWOX11-PagKNAT2/6b Module Bidirectionally Regulates Petiole Traits in Populus

Canopy architecture is a critical determinant of productivity in crops and trees, with leaf positioning being a key factor. Petiole length and angle govern leaf positioning and light interception in many flowering plants, yet the molecular mechanisms that coordinately regulate these two traits in woody plants remain largely unexplored. Here, we show that a transcriptional module in poplar enables bidirectional control over petiole length and angle. Petiole morphogenesis entails a developmental transition from a meristematic state to a differentiation state, a process blocked by the class I KNOX transcription factor PagKNAT2/6b. Using yeast one-hybrid, electrophoretic mobility shift assays, chromatin affinity purification and transient expression assays in tobacco leaves, we provide evidence that WUSCHEL-RELATED HOMEOBOX 11 (PtWOX11) binds the PagKNAT2/6b promoter in vitro and transactivates it in heterologous systems. Transcriptomic and qPCR analyses reveal that PtWOX11 maintains a meristematic transcriptional program and suppresses differentiation genes, including those for cell expansion and wall thickening. Accordingly, overexpression of PtWOX11 produces compact petioles with upright leaf angles, whereas its dominant repression yields hyperelongated petioles with reduced leaf angles. Together, these findings suggest a mechanistic framework for manipulating petiole traits and offer a potential strategy for modifying canopy architecture in bioenergy poplar.