Abstract
Abstract
Poplar adapts to different nitrogen environments by regulating root N uptake and assimilation processes, but the integrated regulatory mechanisms underlying these responses remain unclear. In this study, whole-genome resequencing was performed on 162 poplar germplasm resources (including natural and cultivated germplasm), revealing that the population could be divided into four genetic groups. The cultivated germplasm resources were then subjected to low-nitrogen treatment to identify LN-tolerant germplasm. Integrating genome-wide association studies and weighted gene co-expression network analysis uncovered PagERF173, an AP2/ERF transcription factor, as a pleiotropic gene associated with root traits under LN condition and involved in coordinating nitrate uptake and assimilation. Under LN condition, although PagERF173 mutants and dominant repression line showed lower nitrate uptake and accumulation than the overexpression lines, they exhibited enhanced nitrate assimilation capacity, thereby promoting both shoot and root biomass accumulation. In contrast, PagERF173 overexpression lines displayed the opposite trend. Furthermore, during the N response, PagERF173 activated the expression of PagNRT5.6a, thereby enhancing root nitrate uptake. Meanwhile, PagERF173 interacted with PagNR and PagNiR proteins and inhibited NR and NiR enzymatic activities, thereby suppressing nitrate assimilation. These results reveal that PagERF173 plays an important role in coordinating the balance between root nitrate uptake and assimilation, providing a molecular basis for improving nitrogen use efficiency and breeding for LN adaptation in woody plants.