THE SAL1 GENE OF ARABIDOPSIS, ENCODING AN ENZYME WITH 3'(2'),5'-BISPHOSPHATE NUCLEOTIDASE AND INOSITOL POLYPHOSPHATE 1-PHOSPHATASE ACTIVITIES, INCREASES SALT TOLERANCE IN YEAST

A cDNA library in a yeast expression vector was prepared from roots of Arabidopsis exposed to salt and was used to select Li+-tolerant yeast transformants. The cDNA SAL1 isolated from one of these transformants encodes a polypeptide of 353 amino acid residues. This protein is hom ologous to the HAL2 and CysQ phosphatases of yeast and Escherichia col i, respectively. Partial cDNA sequences in the data bases indicate tha t rice produces a phosphatase highly homologous to SAL1 and that a sec ond gene homologous to SAL1 exists in Arabidopsis. The SAL1 protein ex pressed in E. coli showed 3'(2',5'-bisphosphate nucleotidase and inosi tol polyphosphate 1-phosphatase activities. In yeast, SAL1 restored th e ability of a hal2/met22 mutant to grow on sulfate as a sole sulfur s ource, increased the intracellular Li+ tolerance, and modified Na+ and Li+ effluxes. We propose that the product of SAL1 participates in the sulfur assimilation pathway as well as in the phosphoinositide signal ing pathway and that changes in the latter may affect Na+ and Li+ flux es.