<scp>PdbWRKY31</scp> Positively Regulates Salt Tolerance by Upregulating <i>PdbCATs</i> to Mediate <scp>ROS</scp> Scavenging in <i>Populus davidiana</i>  ×  <i>P. bolleana</i>

WRKY transcription factors (TFs) play a crucial role in mediating plant responses to various environmental stresses, including salt, drought, and heavy metal stresses. In this study, PdbWRKY31 was further identified and characterized from Shanxin poplar (Populus davidiana × P. bolleana). The results of subcellular localization showed that PdbWRKY31 is a nuclear-localized protein. PdbWRKY31 expression in Shanxin poplar under salt stress was obviously induced. To further investigate its function in salt tolerance, an overexpression vector (35S::PdbWRKY31-GFP) was transiently transformed into Shanxin poplar. Physiological indicators showed that overexpression of PdbWRKY31 enhanced peroxidase (POD) and catalase (CAT) activities, reduced hydrogen peroxide (H₂O₂) accumulation, and cell damage induced by salt stress. Y1H and EMSA results demonstrate that PdbWRKY31 specifically bound with the W-box (TTGAC) element. ChIP-PCR and qRT-PCR assays showed that PdbWRKY31 increased PdbCAT1 and PdbCAT3 expression by binding to the W-box element on their promoters. Based on our findings, we proposed a novel regulatory model in which PdbWRKY31 enhanced salt tolerance in Shanxin poplar by binding to the W-box element on the promoter of the target genes (PdbCAT1 and 3) and promoting their expression. This study provided a theoretical foundation for a deeper understanding of the role of WRKY31 TFs and offered insights into breeding highly salt-tolerant plants.