The HKT protein family plays a vital role in plant responses to salt stress by mediating sodium (Na+) and potassium (K+) transport and maintaining Na+-K+ balance. Ipomoea pes-caprae (IPC), a pantropical creeping plant distributed along coastal regions in tropical and subtropical zones, exhibits exceptional salt tolerance. Understanding its salt tolerance mechanisms provides valuable insights for developing salt-tolerant crops and identifying candidate genes for genetic engineering. In this study, we identified two HKT genes, IpcHKT1;1 and IpcHKT1;2, in IPC. Phylogenetic analysis with HKT genes from other Ipomoea species revealed that all analyzed species contain two HKT genes located adjacently on the same chromosome. Comparative analysis of conserved motifs and intron-exon structures indicated that, despite their close evolutionary relationship, the HKT genes in IPC may exhibit functional divergence. Promoter analysis showed that their regulatory regions are enriched with cis-elements associated with responses to biotic and abiotic stresses, hormonal signaling, and growth, highlighting functional diversity within the HKT family. Subcellular localization experiments demonstrated that IpcHKT1;1 and IpcHKT1;2 are ion transporters localized to the plasma membrane. Heterologous expression in yeast confirmed their role in Na+/K+ symporter. Furthermore, RT-qPCR analysis revealed distinct expression patterns under salt stress: IpcHKT1;2 was significantly upregulated in roots, while IpcHKT1;1 expression was transitionally downregulated at 400 mM NaCl treatment. Prolonged high expression of IpcHKT1;2 in roots suggests its critical role in sustained salt stress tolerance. These findings provide new insights into the molecular mechanisms of salt tolerance in IPC. The identification of IpcHKT1;1 and IpcHKT1;2 as key players in salt stress responses offers promising genetic resources for enhancing crop resilience to soil salinity, addressing challenges associated with global salinization.

Nitraria sibirica Pall is a halophytic shrub growing in desert steppe zones. It exhibits extraordinary adaptability to saline-alkali soil, drought, and sand burial. In this study, the high-affinity K+ transporter NsHKT1 was identified and found to play a key role in salt tolerance in N. sibirica. NsHKT1 was used to improve salt tolerance in a poplar hybrid. The expression characteristics of NsHKT1 were analyzed by transforming Arabidopsis and poplar with the beta-glucuronidase (GUS) gene driven by the NsHKT1 promoter. The results showed that NsHKT1 expression was induced by various abiotic stresses and phytohormones. GUS expression was also detected in the reproductive organs of transgenic Arabidopsis, indicating its function in regulating plant reproductive growth. Transgenic 84 K poplar plants overexpressing NsHKT1 exhibited less damage, higher antioxidant capacity, higher chlorophyll and proline levels, and lower malondialdehyde content compared with non-transgenic plants under salt stress. These results are consistent with the salt tolerance results for transgenic Arabidopsis overexpressing NsHKT1, indicating that NsHKT1 plays a key role in salt tolerance in herbaceous and ligneous plants. Inductively coupled plasma-optical emission spectrometry showed a significantly lower leaf Na+ content in transgenic poplar than in the non-transgenic line, revealing that NsHKT1, as a member of HKT family subclass 1, was highly selective to Na+ and prevented shoot Na+ accumulation. Transcriptome analysis indicated that differentially expressed genes in transgenic poplars under salt stress were associated mainly with the isoflavonoid, cutin, suberine, wax, anthocyanin, flavonoid, and cyanoamino biosynthesis pathways, as well as the MAPK signaling pathway, indicating that NsHKT1 not only regulates ion homeostasis but also influences secondary metabolism and signal transaction in transgenic plants.