Abstract
In higher plants, sulfate is converted to adenosine 5'-phosphosulfate (APS) by the action of ATP sulfurylase (ATPS). APS can be a substrate of sulfur reduction, or can be phosphorylated to yield 3'-phosphoadenosine 5'-phosphosulfate, the sulfate donor for sulfation of a range of metabolites. In the Arabidopsis genome, there are four similar genes encoding ATP sulfurylase, ATPS1, ATPS2, ATPS3 and ATPS4. Localization of ATPS was analyzed by expressing ATPS-GFP fusion protein in Arabidopsis plants. ATPS1-GFP, ATPS3-GFP and ATPS4-GFP localized exclusively in plastid, whereas ATPS2-GFP localized in both plastid and cytosol. To investigate the in vivo function of ATPS, knockout mutants were analyzed for ATP sulfurylase activity. The analysis revealed that ATPS1 has the most dominant contribution for total APS production both in leaves and roots. To investigate which isoform is responsible for the APS synthesis in cytosol, we performed subcellular fractionation of leaves of wild-type and mutant plants. Only atps2 mutant showed reduced activity of ATP sulfurylase in cytosol fraction, suggesting that dual-targeting ATPS2 contributes to supply the cytosol with APS.
