Functional Analysis of <i>PdbERF109</i> Gene Regulation of Salt Tolerance in <i>Populus davidiana</i> × <i>P. bolleana</i>

ERF family transcription factors are crucial regulators in plants, playing a central role in abiotic stress responses and serving as important targets for stress-tolerant crop breeding. <i>Populus davidiana</i> × <i>P. bolleana</i>, an elite hybrid poplar cultivar artificially selected in northern China, holds significant research value encompassing ecological restoration, economic industries, genetic resource development, and environmental adaptability. This study identified that <i>PdbERF109</i> expression was significantly upregulated in <i>P. davidiana</i> × <i>P. bolleana</i> response to salt treatment. Furthermore, transgenic poplar lines overexpressing <i>PdbERF109</i> (<i>OE</i>) were generated. Salt stress assays demonstrated that <i>PdbERF109</i> overexpression significantly enhanced salt tolerance in transgenic poplar. Compared to wild-type (WT) plants, <i>PdbERF109</i>-OE lines exhibited a significant enhancement in the activities of antioxidant enzymes, with increases of 2.3-fold, 1.2-fold, and 0.5-fold for superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), respectively, while the levels of malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) were markedly reduced by 39.89% and 40.03%, indicating significantly enhanced reactive oxygen species (ROS) scavenging capacity and reduced oxidative damage. Concurrently, <i>PdbERF109</i> overexpression reduced the natural leaf relative water loss (%). Meanwhile, yeast one-hybrid assays confirmed that the <i>PdbERF109</i> protein specifically binds to GCC-box and DRE cis-acting elements. This study established <i>PdbERF109</i> as a positive regulator of salt stress responses, highlighting its potential as a target gene for improving plant tolerance to high salinity, providing a promising candidate gene for the molecular breeding of salt-tolerant crops.