PdabZIP69 enhances drought tolerance by regulating antioxidant enzyme activity and PdbbHLH1 expression in "Shanxin" poplar.

Plant basic Leucine Zipper (bZIP) proteins are crucial in growth, development, and responses to various abiotic stresses. Extensive research has demonstrated that bZIP transcription factors play a crucial role in mediating plant responses to drought stress. However, to systematically analyze the functions of its family genes, the specific functions of these factors in the drought response of poplar require further investigation. In this study a "Shanxin" poplar bZIP gene, PdabZIP69, was identified which is significantly upregulated under drought stress. Transgenic lines over-expressed PdabZIP69 (OE) were generated through Agrobacterium-mediated transformation. Drought stress assays revealed that PdabZIP69-OE plants exhibit enhanced drought tolerance and reduced leaf water loss compared to wild-type (WT). Physiological analyses revealed that the OE plants exhibited significantly reduced levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA), elevated proline content, as well as enhanced activities of superoxide dismutase (SOD) and peroxidase (POD) when compared to the WT. These results indicate that the augmented reactive oxygen species (ROS) scavenging capacity in PdabZIP69-OE plants confers greater drought tolerance. Y1H, ChIP-PCR and Dual-luciferase assay revealed that PdabZIP69 can bind to the promoter of the PdbbHLH1 gene, a positive regulator of drought tolerance in "Shanxin" poplar, and activate its expression. Collectively, PdabZIP69 enhances drought tolerance in poplar by regulating the antioxidant system and the expression of the PdbbHLH1 gene, providing genetic resources for the systematic study of the regulation of drought resistance of bZIP family members.