De novo biosynthesis of the aggregation pheromone components ipsenol and ipsdienol by the pine bark beetles Ips paraconfusus Lanier and Ips pini (Say) (Coleoptera: Scolytidae).

Abstract

The California five-spined ips, Ips paraconfusus Lanier, produces the myrcene-derived acyclic monoterpene alcohols ipsenol (2-methyl-6-methylene-7-octen-4-ol) and ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol) as components of its aggregation pheromone. The pine engraver beetle, Ipspini (Say), produces only ipsdienol. Previous studies have shown that myrcene, a monoterpene in the pines colonized by these beetles, is a direct precursor to these pheromone components. In vivo radiolabeling studies reported hereshowed that male I. paraconjifsus incorporated [1_14C]acetate into ipsenol, ipsdienol, and amitinol (trans-2-methyl-6-methylene-3,7-octadien-2-ol), while male I. pini incorporated [1-_4C]acetate into ipsdienol and amitinol. Females of these species produced neither labeled nor unlabeled pheromone components. The purified radiolabeled monoterpene alcohols from males were identified by comparison of their HPLC and GC retention times with those of unlabeled standards. HPLCpurified fractions containing the individual radiolabeled components were analyzed by GC-MS and were shown to include only the pure alcohols. To further confirm that ipsdienol and ipsenol were radiolabeled, diastereomeric ester derivatives of the isolated alcohols were synthesized and analyzed by HPLC and GC-MS. After derivatization of the radiolabeled alcohols, the HPLC analysis demonstrated expected shifts in retention times with conservation of naturally occurring stereochemistry. The results provide direct evidence for de novo biosynthesis of ipsenol, ipsdienol, and amitinol by bark beetles. The aggregation pheromone components (4S)-(-)-ipsenol(2-methyl-6-methylene-7-octen-4-ol) (1) and (4S)-( + )-ipsdienol (2-methyl-6-methylene-2,7-octadien-4-ol) (2) were isolated and identified from males of the California five-spined ips, Ips paraconfusus Lanier. These components, together with (1S,2S)-(+)-cis-verbenol (cis-4,6,6-trimethyl bicyclo[3.1.1]-hept-3-en-2-ol), were identified as the first coleopteran pheromone (1). The structural similarity of the acyclic monoterpene alcohols ipsenol and ipsdienol to myrcene (2, 3), a monoterpene present in the oleoresin of the principal host, ponderosa pine, Pinus ponderosa Laws., led to a deuterium labeling study with I. paraconfusus that unequivocally showed the in vivo transformation of myrcene to ipsenol and ipsdienol (4). A more recent labeling study demonstrated the conversion of myrcene to ipsdienol in the male pine engraver beetle, Ips pini (Say) (5). Recent reviews (6-9) emphasize the central role of plant-derived myrcene in the production of ipsenol and ipsdienol, including the hypothesis that myrcene from the host may be sequestered and bioaccumulated by males during early developmental stages for later use as adults (9 consistent with the general concept that monoterpenes sensu stricto are plant products (7,10,11).However, it has been recognized that alternative routes for Ips spp. pheromone biosynthesis may exist, such as de novo biosynthesis or utilization of other terpene hydrocarbo...

Geraniol and Geranial Dehydrogenases Induced in Anaerobic Monoterpene Degradation by Castellaniella defragrans

“…Plants synthesize monoterpenes for thermotolerance or other plant-environment interactions in amounts of over 100 Tg C year Ϫ1 ; thus, they represent an important component in the carbon cycle on earth (33,51,54). In insects, monoterpenes are synthesized as pheromones (4,37,50). Furthermore, these substances are widely used in the food, flavor, and fragrance industries due to their odorous properties (8).…”

High substrate specificity of ipsdienol dehydrogenase (IDOLDH), a short-chain dehydrogenase fromIps pinibark beetles

“…Furthermore, while plants often produce a range of structurally diverse monoterpenes, insect monoterpenoid producers typically synthesize and further modify only myrcene or geraniol (26). For I. pini, pheromone-biosynthetic males produce ipsdienol at daily rates exceeding 1% of their body mass (27). This significant metabolic load is accompanied by strong coordinate up-regulation of the mevalonate pathway (28) as well genes encoding geranyl diphosphate synthase/myrcene synthase (2) and myrcene hydroxylase (6), two committed steps in ipsdienol production.…”

Isolation and functional expression of an animal geranyl diphosphate synthase and its role in bark beetle pheromone biosynthesis

“…Until the last decade, it was widely accepted that bark beetles, in contrast to most other insects (16), derived their monoterpene aggregation pheromones by simple modification of host tree dietary precursors (17,18). However, it is becoming increasingly clear that most pheromone components are synthesized de novo in the anterior midgut tissue (19)(20)(21) of pheromone-producing beetles through the mevalonate pathway (22,23). The allylic C 10 alcohol, ipsdienol, is the major monoterpene-derived aggregation pheromone of male Ips pini ( Fig.…”