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Plant Cell Advance Online Publication
Published on January 25, 2008; 10.1105/tpc.107.055178

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Received August 17, 2007
Returned for revision December 5, 2007
Accepted January 9, 2008

EST Analysis of Hop Glandular Trichomes Identifies an O-Methyltransferase That Catalyzes the Biosynthesis of Xanthohumol

Jana Nagel 1, Lana K. Culley 2, Yuping Lu 2, Enwu Liu 2, Paul D. Matthews 3, Jan F. Stevens 4, and Jonathan E. Page 2*

1 National Research Council–Plant Biotechnology Institute, Saskatoon, Saskatchewan, Canada S7N 0W9; Leibniz Institute of Plant Biochemistry, 06120 Halle/Saale, Germany
2 National Research Council–Plant Biotechnology Institute, Saskatoon, Saskatchewan, Canada S7N 0W9
3 Hopsteiner, S.S. Steiner, New York, New York 10065
4 Department of Pharmaceutical Sciences, Oregon State University, Corvallis, Oregon 97331; Linus Pauling Institute, Oregon State University, Corvallis, Oregon 97331

* To whom correspondence should be addressed. E-mail: jon.page{at}nrc-cnrc.gc.ca.

The glandular trichomes (lupulin glands) of hop (Humulus lupulus) synthesize essential oils and terpenophenolic resins, including the bioactive prenylflavonoid xanthohumol. To dissect the biosynthetic processes occurring in lupulin glands, we sequenced 10,581 ESTs from four trichome-derived cDNA libraries. ESTs representing enzymes of terpenoid biosynthesis, including all of the steps of the methyl 4-erythritol phosphate pathway, were abundant in the EST data set, as were ESTs for the known type III polyketide synthases of bitter acid and xanthohumol biosynthesis. The xanthohumol biosynthetic pathway involves a key O-methylation step. Four S-adenosyl-L-methionine–dependent O-methyltransferases (OMTs) with similarity to known flavonoid-methylating enzymes were present in the EST data set. OMT1, which was the most highly expressed OMT based on EST abundance and RT-PCR analysis, performs the final reaction in xanthohumol biosynthesis by methylating desmethylxanthohumol to form xanthohumol. OMT2 accepted a broad range of substrates, including desmethylxanthohumol, but did not form xanthohumol. Mass spectrometry and proton nuclear magnetic resonance analysis showed it methylated xanthohumol to 4-O-methylxanthohumol, which is not known from hop. OMT3 was inactive with all substrates tested. The lupulin gland-specific EST data set expands the genomic resources for H. lupulus and provides further insight into the metabolic specialization of glandular trichomes.






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