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

Abstract

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.

Gene Expression and Metabolite Profiling of Developing Highbush Blueberry Fruit Indicates Transcriptional Regulation of Flavonoid Metabolism and Activation of Abscisic Acid Metabolism

“…EST sequences were cleaned, clustered, and annotated as described by Nagel et al (2008). Custom PERL scripts were written to assign GO annotation based on top hits to the TAIR database.…”

Terpenoid biomaterials

“…The high density of specialized anatomical structures for terpenoid accumulation is an important agronomic trait for essential oil production. These structures provide easy access to specialized biochemical cell factories for research into terpenoid metabolism and essential oil biosynthesis in general (Gang et al, 2001;Gershenzon et al, 1992;Nagel et al, 2008;Teoh et al, 2006). Typically, the cells adjacent to terpenoid storage sites are thought, or have been shown (e.g.…”

Functional genomics of family 1 glycosyltransferases in Arabidopsis

“…To eliminate problems derived from the transportation of compounds or biased distribution of target compounds between plant tissues, specific or single cell separation techniques may be helpful. In medicinal and aromatic plants, transcriptomics-based approaches with trichome- -(⌬specific transcripts have proved successful in the identification of novel gene functions as some flavonoids and terpenes predominantly accumulate in glandular trichomes (Nagel et al 2008;Rios-Estepa et al 2008;Wang et al 2008). …”