BrPME51a acts downstream of BrAHL14 to modulate root elongation in Chinese cabbage

Plant root development is closely linked to cell wall component modification and structural remodeling. The modulation of the degree of methylesterification of cell wall pectin by pectin methylesterases (PMEs) is key to regulating cell elongation and ultimately the shape of the plant body. Previous studies have demonstrated that AtPME51 encodes a PME involved in root elongation. However, the function of its ortholog in Chinese cabbage, a close relative of Arabidopsis , has yet to be elucidated. In this study, we identified BrPME51a ( BraA02g003170.3.5C ) as the closest ortholog of AtPME51 in Chinese cabbage. BrPME51a contains an N-terminal PMEI domain and a conserved C-terminal PME catalytic domain, and localizes to the Golgi apparatus. BrPME51a is expressed across multiple tissues, with the highest abundance in roots and siliques. Silencing BrPME51a enhanced root elongation in Chinese cabbage, whereas its overexpression in Arabidopsis suppressed primary root growth, demonstrating that BrPME51a negatively regulates root elongation. Furthermore, yeast one-hybrid screening identified the transcription factor BrAHL14 as an upstream factor that binds the BrPME51a promoter. Dual-LUC and GUS transactivation assays confirmed that BrAHL14 represses BrPME51a transcription. Transient overexpression of BrAHL14 in Chinese cabbage downregulated BrPME51a and enhanced root elongation, whereas BrAHL14 silencing upregulated BrPME51a and suppressed root growth. These findings indicate that BrPME51a plays a key role in regulating root growth in Chinese cabbage, acting downstream of the transcriptional repressor BrAHL14. This study provides new insights into the molecular mechanisms by which PME regulate root development in Chinese cabbage.