The putative plasma membrane Na(+)/H(+) antiporter SOS1 controls long-distance Na(+) transport in plants.
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-beta-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.
Shi
Huazhong
H
Department of Plant Sciences, University of Arizona, Tucson, Arizona 85721, USA.
Quintero
Francisco J
FJ
Pardo
Jose M
JM
Zhu
Jian-Kang
JK
D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology; D009154:Mutation; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D018547:Plant Stems / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D012441:Saccharomyces cerevisiae / Q000235:genetics; D012964:Sodium / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000502:physiology*
D008565:Membrane Proteins; D017923:Sodium-Hydrogen Exchangers; D012965:Sodium Chloride; D012964:Sodium