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BIOCHEMICAL PROCESSES AND MACROMOLECULAR STRUCTURES

Terpene Biosynthesis in Glandular Trichomes of Hop^1,2,[W],[OA]

Plant Biology Division, The Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73410 (G.W., L.T., X.D., J.H., P.X.Z., R.A.D.); and Center for Novel Agricultural Products, Department of Biology, University of York, York YO10 5YW, United Kingdom (N.A., P.B., A.K.)

Hop (Humulus lupulus L. Cannabaceae) is an economically important crop for the brewing industry, where it is used to impart flavor and aroma to beer, and has also drawn attention in recent years due to its potential pharmaceutical applications. Essential oils (mono- and sesquiterpenes), bitter acids (prenylated polyketides), and prenylflavonoids are the primary phytochemical components that account for these traits, and all accumulate at high concentrations in glandular trichomes of hop cones. To understand the molecular basis for terpene accumulation in hop trichomes, a trichome cDNA library was constructed and 9,816 cleansed expressed sequence tag (EST) sequences were obtained from random sequencing of 16,152 cDNA clones. The ESTs were assembled into 3,619 unigenes (1,101 contigs and 2,518 singletons). Putative functions were assigned to the unigenes based on their homology to annotated sequences in the GenBank database. Two mono- and two sesquiterpene synthases identified from the EST collection were expressed in Escherichia coli. Hop MONOTERPENE SYNTHASE2 formed the linear monterpene myrcene from geranyl pyrophosphate, whereas hop SESQUITERPENE SYNTHASE1 (HlSTS1) formed both caryophyllene and humulene from farnesyl pyrophosphate. Together, these enzymes account for the production of the major terpene constituents of the hop trichomes. HlSTS2 formed the minor sesquiterpene constituent germacrene A, which was converted to β-elemene on chromatography at elevated temperature. We discuss potential functions for other genes expressed at high levels in developing hop trichomes.

² Any opinions, findings, and conclusions or recommendations expressed in this article are those of the authors and do not necessarily reflect the views of the National Science Foundation.

³ These authors contributed equally to this article.

⁴ Present address: Department of Plant Sciences, Asmundson Hall, Room 221, University of California, 1 Shield Avenue, Davis, CA 95616.

⁵ Present address: Nestlé R & D Center Tours, Plant Science and Technology, 101 Avenue Gustave Eiffel, 7390 Notre-Dame D'Oé, France.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Richard A. Dixon (radixon{at}noble.org).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.125187

^* Corresponding author; e-mail radixon{at}noble.org.

Received June 23, 2008; accepted September 2, 2008; published September 5, 2008.

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