Enzymes of plant gallotannin metabolism

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The accumulation of gallotannins has been documented as a prevalent chemical trait in a range of dicotyledonous plants and simple green algae. Gallotannins, potent protein-complexing polyphenols, form part of the chemical defense against microbial pathogens and herbivores. The biosynthesis of gallotannins depends on the formation of gallic acid and a series of acyltransfer reactions to yield 1,2,3,4,6-penta-O-galloylglucose. In this project we will use homology-based cloning approaches to isolate cDNAs encoding the essential enzymes of this metabolic pathway - dehydroshikimate dehydrogenase, UDP glucose:gallic acid glucosyltransferase and a group of position-specific galloyl transferases, which employ the ß-acetal ester 1-O-galloylglucose as acyl donor. The galloyltransferases form a novel group of plant acyltransferases related to ß-glucosidase-like hydrolases. By site-directed mutagenesis and kinetic characterization of the reaction mechanism the molecular determinants of galloyltransferase activity will be elucidated. The identified sequences will be exploited to transfer the complex gallotannin metabolic pathway to model organisms with the longterm goals to increase plant pathogen resistance and to implement the production of tailored gallotannins for industrial application.