BcAS2 Regulates Leaf Adaxial Polarity Development in Non-Heading Chinese Cabbage by Directly Activating BcPHB Transcription

Leaves are the primary organs for plant photosynthesis, and their flat, symmetric morphology is crucial for plant growth and development. The LBD family transcription factor <i>ASYMMETRIC LEAVES 2</i> (<i>AS2</i>) plays a central role in the establishment of leaf polarity. In this study, we cloned the <i>BcAS2</i> gene from the non-heading Chinese cabbage cultivar "NHCC001" and successfully generated overexpression strains through genetic transformation. Phenotypic analysis revealed that overexpression of <i>BcAS2</i> led to significant upward curling of leaves in non-heading Chinese cabbage. Additionally, we found that the expression of <i>BcPHB</i>, a gene associated with leaf adaxial polarity development, was significantly up-regulated in BcAS2-overexpressing plants compared to controls. This interaction was further confirmed through yeast one-hybridization (Y1H), dual-luciferase reporter assays, and electrophoretic mobility shift assay (EMSA), all of which demonstrated that <i>BcAS2</i> directly binds to the GATA-motif site of the <i>BcPHB</i> promoter and promotes its transcription. Functional validation via overexpression and silencing of <i>BcPHB</i> confirmed its role in regulating adaxial polarity development in non-heading Chinese cabbage leaves. This study elucidates the molecular mechanism of the BcAS2-BcPHB pathway in regulating leaf polarity in non-heading Chinese cabbage, providing a theoretical foundation for morphological improvement breeding.