PagbZIP75 decreases the ROS accumulation to enhance salt tolerance of poplar via the ABA signaling

Poplar (Populus L.) is a fast-growing economic timber plant that is susceptible to salt stress. Here, PagbZIP75 (Potri.014G120800), which was isolated from 84 K poplar and upregulated in response to salt treatment, was investigated by generating overexpression (OE) and repression (RNAi) transgenic lines to elucidate its role in poplar salt stress tolerance through molecular and physiological approaches. PagbZIP75 localized in the nucleus and cell membrane but lacked transcriptional activation activity in yeast cells. Expression pattern analysis revealed that PagbZIP75 was induced by salt stress, peaking at 12 hours in roots and stems and 24 hours in leaves. Under salt stress, OE exhibited enhanced growth and a more robust root system compared to non-transgenic 84 K poplar (WT) and RNAi. DAB and NBT staining results demonstrated lower levels of reactive oxygen species (ROS) in OE leaves, alongwith reduced electrolyte leakage rate and superoxide anion (O₂^-) content, while the proline content and superoxide dismutase (SOD) activity were significantly elevated under salt stress. Based on the RNA-seq data, multilayered hierarchical gene regulatory network (ML-hGRN) around bZIP75 was illustrated and indicated that PagbZIP75 was induced by ABA hormone along with 10 salt-related co-expressed genes. Yeast one-hybrid (Y1H) experiments indicated the binding of PagAREB1 protein to the 0–208 bp upstream fragments of PagbZIP75, and dual luciferase assays (LUC) confirmed a negative interaction between AREB1 and bZIP75. Overall, this study provides a theoretical foundation for the enhancement of poplar salt tolerance by PagbZIP75 through the reduction of ROS accumulation via ABA signaling.