Molecular Genetics of Sulfate Assimilation in Plants

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9601146 Leustek The proposal focuses on the mechanisms of sulfate reduction in higher plants. Specifically in the focus are the two rate-limiting enzymes of this pathway, APS-kinase and PAPS-reductase. Data submitted with the proposal indicated a major breakthrough on the biochemical reactions that govern sulfate reduction - indicating a paradigmatic change in how we have to view this metabolic reaction in plants. The major goal of this proposal is to fortify the preliminary data by an in-depth biochemical study of the enzymatic reactions. Cloned genes are available, encoding the kinase (APK1) and reductase (APR1) enzymes. They will be used to synthesize proteins for biochemical investigations. A major part of the proposal is to over-express the enzymes and/ or to use antisense expression to reduce enzyme amounts in plants. One aspect which may be highly significant is that APR1 is different from its bacterial counterpart in that it has a thioredoxin domain attached - possibly indicating that this enzyme is controlled by the redox state of the cell. This significant new aspect of sulfate metabolism will be analyzed. Sulfate reduction is an important plant metabolism. The reactions provide reduced sulfur for a number of essential plant processes, best known may be sulfur-containing essential amino acids. Effectively reducing sulfate to a less toxic form is also crucial to, for example, trees because sulfate is the major damaging component of acid rain.