Terpene Biosynthesis in Glandular Trichomes of Hop    

Abstract

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 beta-elemene on chromatography at elevated temperature. We discuss potential functions for other genes expressed at high levels in developing hop trichomes.

Heterodimeric geranyl(geranyl)diphosphate synthase from hop ( Humulus lupulus ) and the evolution of monoterpene biosynthesis

“…GPP could be used for monoterpene biosynthesis, and GGPP could be used for biosynthesis of diterpenes, chlorophylls, plastoquinone, and phylloquinone (22), or be involved in protein prenylation. However, myrcene synthase is expressed at a significantly higher level than the heterodimeric GPPS subunits in hop lupulin glands (18), and it has a higher affinity for GPP than does the heterodimeric GPPS. Furthermore, there are no ESTs that hit other GPPS/GGPPS-like genes in a new database (http:// trichome.noble.org/trichomedb) comprising 22,959 sequences from hop trichomes.…”

“…Myrcene is synthesized and stored exclusively in lupulin glands (trichomes on the inner surface of the bracts of the female flowers). The tissue-specific and developmental expression profiles of a hop monoterpene synthase suggested a primary role in myrcene formation (18).…”

Morphogenesis, volume and number of hop (Humulus lupulus L.) glandular trichomes, and their influence on alpha-acid accumulation in fresh bracts of hop cones

“…5). The cause of such a phenomenon could be an increase of the partial pressure of liquids and gasses on the cell walls inside peltate glandular trichomes during the biosynthesis of terpene-derived natural products, particularly a-acids which are the final product in the carbon pathway of terpene-derived natural products (WANG et al 2008). This could be an 6 ACTA BOT.…”

“…Peltate glandular trichomes are micro bodies of spheroid and spherical shape on the epidermis of hop cone bracts in which the hop metabolites are accumulating PAIS 1988, 1990;^EH et al 2007;WANG et al 2008). Seven morphological development stages of peltate glandular trichomes are described and the relation between their morphogenesis and accumulation of secondary metabolites was clarified .…”

“…Activity of VPS gene (valerophenone synthase), which is involved in the first steps of bitter resin (a-acid) biosynthesis, was strong when the cuticle was slightly detached from the glandular head cells. WANG et al (2008) described three biosynthetic pathways for terpene-derived natural products found in hop trichomes and activity of VPS gene is obvious in C pathway of terpene-derived natural products. The final step of carbon pathway is the biosynthesis of humulone or a-acids.…”