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 NaCI-containing agar plates.These mutants (sosl-7, sosl-2, sosl-3, and sosl-4) are allelic to each other and were caused by single recessive nuclear mutations.The SOSl gene was mapped to chromosome 2 at 29.5 f 6.1 centimorgans.The mutants showed no phenotypic changes except that their growth was >20 times more sensitive to inhibition by NaCI.Salt hypersensitivity is a basic cellular trait exhibited by the mutants at all developmental stages.The sosl mutants are specifically hypersensitive to Na+ and Li+.The mutants were unable to grow on media containing low levels (below 4 mM) of potassium.Uptake experiments using B6Rb showed that sosl mutants are defective in high-affinity potassium uptake.sosl plants became deficient in potassium when treated with NaCI.The results demonstrate that potassium acquisition is a critical process for salt tolerance in glycophytic plants.