SOS1, a Genetic Locus Essential for Salt Tolerance and Potassium Acquisition

To begin to determine which genes are essential for salt tolerance in higher plants, we identified four salt-hypersensitive mutants of Arabidopsis by using a root-bending assay on NaCl-containing agar plates. These mutants (sos1-1, sos1-2, sos1-3, and sos1-4) are allelic to each other and were caused by single recessive nuclear mutations. The SOS1 gene was mapped to chromosome 2 at 29.5 [plusmn] 6.1 centimorgans. The mutants showed no phenotypic changes except that their growth was >20 times more sensitive to inhibition by NaCl. Salt hypersensitivity is a basic cellular trait exhibited by the mutants at all developmental stages. The sos1 mutants are specifically hypersensitive to Na+ and Li+. The mutants were unable to grow on media containing low levels (below ~1 mM) of potassium. Uptake experiments using 86Rb showed that sos1 mutants are defective in high-affinity potassium uptake. sos1 plants became deficient in potassium when treated with NaCl. The results demonstrate that potassium acquisition is a critical process for salt tolerance in glycophytic plants.