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

## TL;DR

This study shows how the BcAS2 gene controls leaf shape in non-heading Chinese cabbage by activating another gene called BcPHB.

## Contribution

The study identifies BcAS2 as a direct activator of BcPHB, revealing a new molecular pathway for leaf polarity regulation in non-heading Chinese cabbage.

## Key findings

- Overexpression of BcAS2 causes upward leaf curling in non-heading Chinese cabbage.
- BcAS2 directly binds to the BcPHB promoter and activates its transcription.
- BcPHB is confirmed to regulate leaf adaxial polarity development.

## Abstract

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 ASYMMETRIC LEAVES 2 (AS2) plays a central role in the establishment of leaf polarity. In this study, we cloned the BcAS2 gene from the non-heading Chinese cabbage cultivar “NHCC001” and successfully generated overexpression strains through genetic transformation. Phenotypic analysis revealed that overexpression of BcAS2 led to significant upward curling of leaves in non-heading Chinese cabbage. Additionally, we found that the expression of BcPHB, 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 BcAS2 directly binds to the GATA-motif site of the BcPHB promoter and promotes its transcription. Functional validation via overexpression and silencing of BcPHB 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.