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

ABSTRACT 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 3 ) 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 3 stress response, indicating its potential as a candidate for improving stress tolerance in forest plants.