PcabHLH58/PcabHLH151 regulates adventitious root development and nitrogen uptake in poplar

As a crucial ecological shelterbelt and timber species in China, Populus relies on adventitious root (AR) formation and root architecture for its ecological adaptability and clonal propagation efficiency. Two key root trait-related genes, PcabHLH58 and PcabHLH151, were identified through genome-wide association studies (GWAS) in Populus cathayana. Single or double mutations of PcabHLH58 and PcabHLH151 significantly inhibited AR development and nitrogen uptake in poplar. Furthermore, both genes can form homodimers or heterodimers to modulate the expression of PcaSCL33 and PcaPLT1 during AR development. The higher expression level and stronger regulatory capacity of PcabHLH58 imply its more critical role in the AR development. Additionally, PcaWOX5 was found to be modulated through both the PcabHLH58/PcabHLH151-PcaSCL33/PcaSHR and PcabHLH58/PcabHLH151-PcaPLT1 pathway. PcaPAR1 was identified as a feedback regulatory node in modulating the regulatory activities of both PcabHLH58 and PcabHLH151. Collectively, this study elucidates a novel regulatory network involving root development in poplar and provides foundational insights for future genetic breeding efforts.