A MYB-Related Transcriptional Module Cooperatively Represses Xylem Development in Poplar.

MYB transcription factors play crucial roles in regulating plant growth and development, but the functions of the MYB-related subfamily in woody plants remain poorly understood. In this study, we characterized PagMYBR028, an MYB-related transcription factor from poplar '84 K' (Populus alba × Populus glandulosa), which was predominantly expressed in leaves and xylem. Compared with WT plants, PagMYBR028-overexpressing transgenic poplar exhibited reduced leaf area and retarded secondary xylem development, whereas PagMYBR028-RNAi lines displayed the opposite phenotypes. Further analysis revealed that PagMYBR028 interacts with PagMYBR005, a related regulator with overlapping functions in poplar development. Both proteins directly repress the expression of PagGRF12b, and their interaction enhances this transcriptional repression. In addition, overexpression of PagGRF12b promoted secondary cell wall deposition. Taken together, our results delineate a PagMYBR028-PagMYBR005-PagGRF12b module that coordinately regulates poplar growth and secondary wall development, providing new insights into the transcriptional network underlying wood formation and a theoretical basis for molecular breeding in trees.