MdJUB1 positively regulates salt stress in apple by increasing GABA contents and stabilizing Na +/K+ homeostasis

Abstract Soil salinization represents a significant constraint on global agricultural development. Although several NAC gene families have been implicated in the response to salt stress, the mechanisms underlying salt stress tolerance remain unclear, particularly in perennial fruit trees. In this study, we identify MdJUB1, a NAC transcription factor, as a key regulator of salt stress response in apple. Under salt stress, MdJUB1 increases γ-aminobutyric acid (GABA) content, thereby positively regulating salt stress tolerance in apple. Further analysis using yeast one-hybrid, luciferase assays, and electrophoretic mobility shift assays demonstrated that MdJUB1 directly binds to the promoter of MdGAD1, promoting GABA synthesis. Additionally, under salt stress, overexpression of MdJUB1 increased the Na+/K+ ratio in apple. MdJUB1 also binds to the promoters of MdNHX1, MdHKT1, and MdSOS3, activating their expression. Using yeast two-hybrid screening, we identified MdDOF2.4 as an interactor of MdJUB1 and found that MdDOF2.4 positively regulates salt stress tolerance. Importantly, the interaction between MdDOF2.4 and MdJUB1 enhances the expression of downstream genes, including MdGAD1, MdNHX1, MdHKT1, and MdSOS3. Our results demonstrate that MdJUB1 is involved in the regulation of GABA levels and the maintenance of Na+/K+ homeostasis, which may contribute to enhanced salt tolerance in apple.