| Summary: | High salinity restricts plant growth and geographic distribution. Plant intracellular Na<sup>+</sup>/H<sup>+</sup> (NHX) antiporters have critical roles in plant development and stress response. However, the molecular functions of <i>RmNHXs</i> in <i>Rosa multiflora</i> remain unclear. In this study, we identified 11 putative <i>RmNHXs</i> in <i>R. multiflora</i> according to the genome-wide analysis. The <i>RmNHX</i>s were classified into three classes. Most of the <i>RmNHX</i>s were responsive to salt stress, with the greatest upregulation being observed in <i>RmNHX2</i>. <i>RmNHX2</i> was localized at the tonoplast. <i>RmNHX2</i> overexpression resulted in the enhanced salt tolerance in tobacco, whereas virus-induced gene silencing (VIGS) of <i>RmNHX2</i> in <i>R. multiflora</i> elevated salt susceptibility. Under salt treatment, the transgenic tobaccos achieved less reactive oxygen species (ROS) accumulation and higher activities of antioxidant enzymes, which complied with the upregulated expressions of antioxidant genes. Moreover, <i>RmNHX2-</i>overexpression lines had a lower level of Na<sup>+</sup>, a higher level of K<sup>+</sup>, and a lower Na/K ratio. In contrast to the mentioned, VIGS of <i>RmNHX2</i> in <i>R. multiflora</i> exhibited the opposite phenotype, accompanied by a compromised salt tolerance. Regarded together, these results demonstrate that <i>RmNHX2</i> enhances plant salt tolerance by maintaining proper ion homeostasis, as well as by accelerating ROS scavenging.
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