The Putative Plasma Membrane Na⁺/H⁺ Antiporter SOS1 Controls Long-Distance Na⁺ Transport in Plants

• Published in: The Plant cell 2002-02, Vol.14 (2), p.465-477
• Main Authors: Shi, Huazhong, Quintero, Francisco J., Pardo, Jose M., Zhu, Jian-Kang
• Format: Article
• Language: English
• Subjects: Antiporters; Arabidopsis - genetics; Arabidopsis - metabolism; Biological Transport - drug effects; Cell membranes; Cloning, Molecular; Epidermal cells; Gene Expression Regulation, Plant; Genetic Complementation Test; Membrane Proteins - genetics; Membrane Proteins - physiology; Mutation; Plant cells; Plant Leaves - genetics; Plant Leaves - metabolism; Plant roots; Plant Roots - genetics; Plant Roots - metabolism; Plant Stems - genetics; Plant Stems - metabolism; Plants; Plants, Genetically Modified; Root tips; Saccharomyces cerevisiae - genetics; Sodium - metabolism; Sodium Chloride - pharmacology; Sodium-Hydrogen Exchangers - genetics; Sodium-Hydrogen Exchangers - physiology; Transgenic plants; Xylem; Yeasts
• ISSN: 1040-4651; 1532-298X
• DOI: 10.1105/tpc.010371

The salt tolerance locus SOS1 from Arabidopsis has been shown to encode a putative plasma membrane Na+/ H+ antiporter. In this study, we examined the tissue-specific pattern of gene expression as well as the Na+ transport activity and subcellular localization of SOS1. When expressed in a yeast mutant deficient in endogenous Na+ transporters, SOS1 was able to reduce Na+ accumulation and improve salt tolerance of the mutant cells. Confocal imaging of a SOS1-green fluorescent protein fusion protein in transgenic Arabidopsis plants indicated that SOS1 is localized in the plasma membrane. Analysis of SOS1 promoter-β-glucuronidase transgenic Arabidopsis plants revealed preferential expression of SOS1 in epidermal cells at the root tip and in parenchyma cells at the xylem/symplast boundary of roots, stems, and leaves. Under mild salt stress (25 mM NaCl), sos1 mutant shoot accumulated less Na+ than did the wild-type shoot. However, under severe salt stress (100 mM NaCl), sos1 mutant plants accumulated more Na+ than did the wild type. There also was greater Na+ content in the xylem sap of sos1 mutant plants exposed to 100 mM NaCl. These results suggest that SOS1 is critical for controlling long-distance Na+ transport from root to shoot. We present a model in which SOS1 functions in retrieving Na+ from the xylem stream under severe salt stress, whereas under mild salt stress it may function in loading Na+ into the xylem.