Overexpression of high affinity K+ transporter from Nitraria sibirica enhanced salt tolerance of transgenic plants

Abstract

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 β-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.

Keywords: HKT1; Nitraria sibirica; Promoter; Salt tolerance; Transgenic poplar.