The V-Type H+-Transporting ATPase Gene PoVHA-a3 from Portulaca oleracea Confers Salt Tolerance in Arabidopsis thaliana Through the Modulation of BR-ABA Signaling Balance

Vacuolar H+-ATPases play crucial roles in plant ion homeostasis and stress adaptation, yet the functional characterization of their subunit genes in purslane remains limited. In this study, PoVHA-a3, encoding a tonoplast-localized V-ATPase a3 subunit, was identified as a key salt-responsive gene through transcriptomic analysis. Integrated bioinformatic analysis and molecular docking simulations predicted specific binding of NAC3, MYB1, and bHLH62 to the PoVHA-a3 promoter, suggesting their synergistic role in regulating PoVHA-a3 expression. Under salt stress, PoVHA-a3 transgenic Arabidopsis lines exhibited elevated endogenous abscisic acid levels and upregulation of signaling genes (AtNCED3, AtRD29A, AtCOR15A), while the brassinosteroid signaling pathway was suppressed, as indicated by the reduced expression of AtBZR1 and AtEXPA8. Meanwhile, the transgenic lines demonstrated enhanced ATP levels, respiratory rate, and V-ATPase activity. In addition, PoVHA-a3 expression led to greater accumulation of osmoprotectants (proline, soluble sugars and proteins), higher activities of antioxidant enzymes, and reduced levels of oxidative stress indices. Furthermore, a significantly lower shoot Na+/K+ ratio was observed in transgenic plants, indicating improved ion homeostasis. In conclusion, this study demonstrates that PoVHA-a3 acts as a pivotal positive regulator of salt tolerance in purslane, providing a valuable genetic resource for enhancing salt tolerance in crops through genetic engineering.