CmCYC2d is a Regulator of Leaf Abaxial Curling in Chrysanthemum morifolium

Leaf morphology is crucial for plant photosynthesis and stress adaptation. While CIN-like TCP transcription factors are well-known for their roles in leaf curling and morphogenesis, the function of CYC-like TCPs in leaf development remains largely unexplored. This study identifies CmCYC2d as a key regulator of abaxial leaf curling in Chrysanthemum morifolium. Phenotypic analysis revealed that the downward curling observed in OX-CmCYC2d transgenic lines was primarily due to the enlargement of adaxial epidermal cells. Furthermore, a reduction in epidermal cell number was identified as a significant contributor to the smaller leaf area in these plants. Transcriptome and WGCNA analyses highlighted CmSAUR55 as a potential downstream target of CmCYC2d. ChIP-qPCR, EMSA, and LUC assays confirmed that CmCYC2d directly bound to the CmSAUR55 promoter. Additionally, transcriptome data revealed that the reduced cell number in OX-CmCYC2d transgenic lines may be mediated by auxin-related pathways and key genes such as CNR7. The CmCYC2d-CmSAUR55 module was also closely linked to the development of enlarged adaxial epidermal cells in the leaf sinus, emphasising its role in this developmental process. This study highlights the regulatory role of CmCYC2d in leaf development and sheds light on the molecular mechanisms underlying leaf curling in chrysanthemum.