Hst1At (accession number AB018695) was identified from the Arabidopsis thaliana sequencing project on BAC T3F12, and the corresponding cDNA was isolated by reverse transcription-PCR. Southern blot analysis reveals a single copy of this gene. The cDNA encodes a root specific sulfate transporter of 649 amino acids. Heterologous expression of hst1At in a sulfate transport deficient yeast mutant shows that this gene encodes a high-affinity transport system ( approximately 2 microM). The transcript relative abundance increases in roots in response to sulfate deprivation, which correlated with increased root SO(4)(2-) influx capacity. These patterns were reversed upon sulfate addition to the medium and were accompanied by an increased glutathione level in roots. Feeding plants with cysteine or glutathione led to similar responses. Using buthionine sulfoximine, an inhibitor of glutathione synthesis, we show that glutathione rather than cysteine controls hst1At expression.