Overexpression of BpWOX4 Enhances Salt Stress Tolerance in Betula platyphylla

Salt stress represents one of the most prevalent and detrimental abiotic factors that induce oxidative damage, ionic toxicity, and osmotic imbalance, thereby impairing plant growth and development in natural environments. In this study, we investigated the functional role of the BpWOX4 gene in conferring salt stress tolerance in Betula platyphylla . Overexpression (OE) and suppression (SE) constructs of BpWOX4 were generated and introduced into birch via Agrobacterium -mediated zygotic embryo transformation. A total of 11 OE and 3 SE transgenic lines were obtained, and evaluated under salt stress conditions. Results demonstrated that OE lines exhibited significantly enhanced tolerance to salt stress. Under salt stress conditions, the physiological indices of fresh and dry weight and chlorophyll content in BpWOX4 OE transgenic lines were significantly higher than those in wild-type (WT) and SE lines. Antioxidant enzyme assays further showed elevated superoxide dismutase (SOD) and peroxidase (POD) activities in OE lines, ranging from 1.19- to 1.54-fold higher, accompanied by 39–44% reduction in malondialdehyde (MDA) levels relative to WT. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed that the expression level of the BpWOX4 gene in OE transgenic lines was significantly elevated compared with that in WT following salt stress treatment. These findings indicate that BpWOX4 positively regulates salt tolerance in Betula platyphylla , substantially enhancing its resistance to salt stress, thereby establishing a foundation for future comprehensive studies of stress resistance mechanisms in Betula platyphylla .