Functional characterization of a Na+/H+ antiporter salt overly sensitive 1 gene, LpSOS1, involved in positively regulating salt response from Lilium pumilum

Abstract Lilium pumilum has a strong salt tolerance. However, its molecular mechanisms underlying salt tolerance remain unexplored. In this study, a plasma membrane Na+/H+ antiporter gene, LpSOS1, was cloned from L. pumilum. The expression level of LpSOS1 in L. pumilum was significantly upregulated in the presence of high NaCl concentrations (100 mM). Localisation analysis in tobacco epidermal cells showed that the LpSOS1 protein was found in the plasma membrane. Overexpression of LpSOS1 in Arabidopsis enhanced tolerance to salt stress, as indicated by a lower malondialdehyde content; higher levels of the related antioxidant reductases superoxide dismutase, peroxidase, and catalase; and a decreased Na+/K+ ratio in transgenic plants. SOS1 mutant and wild-type (WT) Arabidopsis plants expressing LpSOS1 grew better, with higher biomass, root length, and lateral root quantity, when treated with NaCl, whereas WT and SOS1 mutant Arabidopsis plants were wilted, chlorotic, and even died under salt stress. Moreover, the transcript levels of stress-related genes were significantly higher in LpSOS1-overexpressing lines than in WT plants under salt stress. These results suggest that LpSOS1 improves plant salt tolerance by regulating ion homeostasis, reducing Na+/K+ in plants, protecting the plasma membrane from oxidative damage under salt stress, and enhancing antioxidant enzyme activity.