Constitutive Expression of a Grapevine Stilbene Synthase Gene in Transgenic Hop (Humulus lupulusL.) Yields Resveratrol and Its Derivatives in Substantial Quantities

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Abstract
Resveratrol, a well-known phytoalexin and antioxidant, is produced by the action of stilbene synthase (STS) in some plant species. Hop (Humulus lupulus L.) plants of the Tettnang variety were transformed with a gene encoding for STS from grapevine. Under the control of the constitutive 35S cauliflower mosaic virus promoter, expression of the transgene resulted in accumulation of resveratrol and high levels of its glycosylated derivatives in leaves and inflorescences. Piceid, the predominant derivative, reached a concentration of up to 560 μg/g of fresh weight (f.w.) in hop cones, whereas no stilbenes were detected in nontransformed controls (wild-type). In transgenic plants the amounts of α- and β-acids, naringenin chalcone, and prenylated flavonoids did not change significantly when compared with nontransformed plants. Transgenic plants showed normal morphology and flower development as did the nontransformed controls. The results clearly show that in hop constitutive expression of sts interferes neither with plant development nor with the biosynthesis of secondary metabolites relevant for the brewing industry. Since resveratrol is a well-known phytoalexin and antioxidant, sts transgenic hop plants could display enhanced pathogen resistance against microbial pathogens, exhibit new beneficial properties for health, and open new venues for metabolic engineering. Keywords: Phytoalexin; antioxidant; prenylation; flavonoid; Agrobacterium tumefaciens; tissue culture