The Advantaged Salt Inducible Suaeda salsa SsNRT2.5 and Its Promoter Significantly Enhance Nitrate Transport Efficiency and Salt Tolerance in Transgenic Arabidopsis and Rice

Efficient nitrogen (N) uptake is critical for crop yield, but soil salinization inhibits plant nitrogen acquisition. In this study, the nitrate (NO₃ ⁻) transporter gene SsNRT2.5 and its promoter from the halophyte Suaeda salsa was investigated to elucidate the functional role in NO₃ ⁻ transport under salinity and low NO₃ ⁻-N conditions. SsNRT2.5 and its promoter were cloned and transformed into Arabidopsis thaliana and rice (Oryza sativa L.) for functional identification, which included analyses of expression patterns, promoter cis-element characterisation and phenotypic assessments under salt and low NO₃ ⁻-N conditions. SsNRT2.5 expression was significantly upregulated under salt stress and low NO₃ ⁻-N conditions in S. salsa, which improved NO₃ ⁻ transport in trangenic Arabidopsis thaliana and rice. Its promoter contained salt-responsive (e.g., GT-1, DRE) and N-related (e.g., GATABOX) elements, which drove stronger salt-induced NRT2.5 expression than AtNRT2.5 promoter. Transgenic Arabidopsis and rice with SsNRT2.5 and its promoter showed enhanced NO₃ ⁻ accumulation, reduced Na⁺ toxicity, and higher salt tolerance, as well as improved seed NO₃ ⁻ storage and viability compared to WT. SsNRT2.5 plays a key role in the adaptation of S. salsa to high saline and nitrogen-limited environments, offering valuable genetic resources and theoretical insights for breeding salt-tolerant crops and developing sustainable saline agriculture.