PhYAB4 directly activates PhAGL6‐2 to regulate lip‐related organ curvature morphology in Paphiopedilum henryanum

Summary The orchid lip is a highly specialized floral organ that contributes to floral architecture and pollinator interaction. However, the developmental and molecular mechanisms underlying lip‐related organ curvature in Paphiopedilum remain poorly understood. Using Paphiopedilum henryanum and its Type A peloric mutant, we found that visible divergence between wild‐type petals and mutant lip‐like petals begins at Stage 4. Curvature was associated with adaxial–abaxial epidermal cell number imbalance in the distal region, whereas average epidermal cell area remained largely unchanged. Transcriptome and expression analyses identified PhAGL6‐2 as a lip‐associated AGL6 homolog enriched in lips and lip‐like petals during Stages 4–5. PhAGL6‐2 was preferentially expressed on the abaxial side, particularly in regions associated with curvature. Virus‐induced gene silencing‐mediated silencing of PhAGL6‐2 in Dendrobium Chao Praya Smile and P. henryanum affected perianth organ curvature, suggesting a broader role in floral organ morphogenesis. The YABBY transcription factor PhYAB4 directly bound the AGTGTG motif in the PhAGL6‐2 promoter and activated its transcription. Silencing PhYAB4 reduced PhAGL6‐2 expression and caused stronger floral curvature, lip outgrowths, and partial disruption of floral symmetry. These findings identify a PhYAB4– PhAGL6‐2 pathway associated with epidermal cell number imbalance and lip‐related organ curvature.