Genome-Wide Identification of The NHXs in Rosa Multiflora Reveals a Key Role of RmNHX2 in Salt Tolerance

Abstract High salinity restricts plant growth and geographic distribution. Plant intracellular Na+/H+ (NHX) antiporters have critical roles in plant development and stress response. However, the molecular functions of RmNHXs in Rosa multiflora remain obscure. In this study, we identified 11 putative RmNHXs in Rosa multiflora according to the genome-wide analysis. The RmNHX genes were classified into 3 classes. Most of the RmNHX genes were responsive to salt stress, with the greatest up-regulation being observed in RmNHX2. RmNHX2 was localized at the tonoplast. RmNHX2 overexpression resulted in the enhanced salt tolerance in tobacco, whereas virus-induced gene silencing (VIGS) of RmNHX2 in R.multiflora increasedsalt susceptibility. Under salt treatment, the transgenic tobacco plants achieved less reactive oxygen species (ROS) accumulation and higher activities of enzymes (e.g., superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT)), which complied with the up-regulated expressions of antioxidant genes. In addition, RmNHX2-overexpression lines had a lower level of Na+, a higher level of K+, as well as a lower Na/K ratio. In contrast to the mentioned, VIGS of RmNHX2 in R.multiflora exhibited the opposite phenotype, accompanied by compromised salt tolerance. RmNHX2 enhances plant salt tolerance by maintaining proper ion homeostasis, as well as by accelerating ROS scavenging. For this reason, RmNHX2 has great potential to be employed for the engineering of ornamental plants in terms of enhanced salt tolerance subsequently.