Halophyte Halogeton glomeratus HKT1;2 confers salt tolerance in transgenic Arabidopsis by modulating ion homeostasis

• HgHKT1;2 is an HKT gene family from Halogeton glomeratus and localizes to the endoplasmic reticulum (ER) in Arabidopsis protoplasts. • Heterologous expression of HgHKT1;2 enhances yeast salt tolerance by mediating Na⁺ efflux. • Overexpression of HgHKT1;2 in Arabidopsis improves salt tolerance, as evidenced by better germination, root growth, optimized K⁺/Na⁺ ratio, and improved ion flux dynamics under 150 mM NaCl stress (via NMT). • Transgenic Arabidopsis exhibits elevated antioxidant enzyme activities and osmolyte accumulation, synergistically alleviating oxidative and osmotic stress damage. • HgHKT1;2 confers salt tolerance by coordinating ion homeostasis and stress-responsive pathways, serving as a promising candidate for crop salt-tolerance engineering. The HKT (high-affinity potassium transporter) gene family plays a critical role in regulating ion homeostasis under salt stress, yet its functional mechanisms in the halophyte Halogeton glomeratus remain largely uncharacterized. Here, we combined bioinformatics and expression profiling to identify HgHKT1;2 as a key candidate gene significantly induced in roots under 150 mM NaCl stress. Subcellular localization in Arabidopsis protoplasts indicated that HgHKT1;2 is primarily localized to the endoplasmic reticulum (ER). Heterologous expression in Na⁺-sensitive (AXT3) and K⁺-uptake-deficient (CY162) yeast strains demonstrated that HgHKT1;2 enhances salt tolerance by mediating Na⁺ efflux to reduce cellular Na⁺ accumulation. Transgenic Arabidopsis overexpressing HgHKT1;2 exhibited improved germination, root growth, and elevated K⁺/Na⁺ ratios under salinity, which is attributed to enhanced Na⁺ exclusion and reduced K⁺ loss in both roots and leaves. Furthermore, under salt stress, transgenic Arabidopsis showed significantly enhanced activities of key antioxidant enzymes (superoxide dismutase, peroxidase, catalase) and increased accumulation of osmolytes (proline, soluble sugar) compared with the wild type, which synergistically alleviates oxidative damage and osmotic stress caused by ion imbalance. Our results indicate that HgHKT1;2 plays an essential role in conferring salt tolerance by coordinating ion homeostasis and stress-responsive physiological pathways, highlighting its potential as a candidate gene for improving salt tolerance in crops.