DISSECTING TERPENOPHENOLIC BIOSYNTHESIS IN HOP LUPULIN GLANDS USING EST GENOMICS

Abstract

The hop plant (Humulus lupulus) is rich in terpenophenolic natural products including the bitter acids that flavour beer and xanthohumol, a prenylated flavonoid with potent anticancer properties. Most terpenophenolics found in hop are synthesized and stored in glandular trichomes (lupulin glands) that develop on female cones. Our research applies trichome-focused genomics to elucidate the metabolic pathways leading to these metabolites and to identify the enzymes catalyzing key biosynthetic steps. We sequenced 10,581 expressed sequence tags (ESTs) derived from hop lupulin gland-specific cDNA libraries and analyzed them for the presence of biosynthetic enzymes. ESTs representing enzymes of terpenoid biosynthesis, including all of the steps of the methyl 4-erythritol phosphate (MEP) pathway, were abundant in the EST dataset, as were the known polyketide synthases of bitter acid and xanthohumol biosynthesis. We have used the EST dataset to uncover a novel enzyme, desmethylxanthohumol O-methyltransferase, which catalyzes the final step in xanthohumol formation. These studies both highlight the value of applying genomics to medicinal plants and provide further insight into the metabolic specialization of glandular trichomes.