PagGRF12a interacts with PagGIF1b to regulate secondary xylem development through modulating PagXND1a expression in Populus alba × P. glandulosa

Growth‐regulating factors (GRFs) are important regulators of plant development and growth, but their possible roles in xylem development in woody plants remain unclear. Here, we report that Populus alba × Papulus glandulosa PagGRF12a negatively regulates xylem development in poplar. PagGRF12a is expressed in vascular tissues. Compared to non‐transgenic control plants, transgenic poplar plants overexpressing PagGRF12a exhibited reduced xylem width and plants with repressed expression of PagGRF12a exhibited increased xylem width. Xylem NAC domain 1 (XND1) encodes a NAC domain transcription factor that regulates xylem development and transcriptional analyses revealed that PagXND1a is highly upregulated in PagGRF12a‐overexpressing plants and downregulated in PagGRF12a‐suppressed plants, indicating that PagGRF12a may regulate xylem development through PagXND1a. Transient transcriptional assays and chromatin immunoprecipitation‐polymerase chain reaction assays confirmed that PagGRF12a directly upregulates PagXND1a. In addition, PagGRF12a interacts with the GRF‐Interacting Factor (GIF) PagGIF1b, and this interaction enhances the effects of PagGRF12a on PagXND1a. Our results indicate that PagGRF12a inhibits xylem development by upregulating the expression of PagXND1a. The growth‐regulating factor PagGRF12a participates in the regulation of secondary xylem development through physically interacting with PagGIF1b and co‐regulating the target gene PagXND1a, providing a mechanistic insight into the regulation of wood formation.