Abstract
Higher plants take up sulfate and convert it to adenosine 5'-phosphosulfate (APS). APS can be a substrate of sulfur reduction, or can be phosphorylated by APS kinase to yield 3'-phosphoadenosine 5'-phosphosulfate (PAPS), a donor for sulfation of a range of metabolites. There are four APS kinase genes, AKN1, AKN2, AKN3 and AKN4 in Arabidopsis genome. The isolated recombinant proteins of AKN1, AKN2, AKN3 and AKN4 independently catalyzed an APS kinase reaction. The mRNA levels of AKN2 significantly decreased under sulfur-deficient conditions. Transgenic Arabidopsis plants expressing fusion gene construct of AKN promoter-AKN coding sequence-GFP were generated to analyze organellar-specific and cell type-specific expression of APS kinases. Localization of AKN-GFP fusion proteins suggested that AKN1, AKN2 and AKN4 expressed in plastids whereas AKN3 localized in cytosol. In addition, cell type-specificities of AKN isozymes were different from each other, suggesting that each AKN isozyme plays a specific role in the PAPS synthesis.
