Elucidating the Role and Regulatory Mechanism of BpbZIP5 in the Saline-Alkaline Stress Response in Betula platyphylla.

Saline-alkali conditions are regarded as among the most serious abiotic stressors that impede plant growth and lead to substantial reductions in plant yields. The bZIP transcription factor (TF) exerts a crucial function in plant adaptation to various environmental stresses. However, its function and mechanisms in conferring tolerance to saline-alkali (NaHCO) stress remain insufficiently characterized. This study demonstrates that the BpbZIP5 TF from Betula platyphylla exhibits significant responsiveness to saline-alkali stress. Overexpression of BpbZIP5 correlates positively with saline-alkali stress tolerance by facilitating reactive oxygen species (ROS) elimination and maintaining ion homeostasis in B. platyphylla. Moreover, BpbZIP5 is vital in controlling stomatal aperture, thereby enhancing resistance to saline-alkali conditions. The qRT-PCR and RNA sequencing (RNA-seq) analyses reveal that BpbZIP5 regulates the expression of genes associated with stress tolerance. Through TF-centered yeast one-hybrid analysis, BpbZIP5 demonstrates interaction with four novel elements. Additional research confirms that BpbZIP5 modulates downstream gene expression through specific element interactions, as verified by chromatin immunoprecipitation (ChIP) and β-glucuronidase (GUS) activity. This investigation provides novel insights into the function and mechanism of BpbZIP5 in NaHCO stress response, indicating its potential as a candidate for improving stress tolerance in forest plants.