Midgut tissue of male pine engraver, Ips pini, synthesizes monoterpenoid pheromone component ipsdienol de novo

Abstract

For over three decades the site and pathways of bark beetle aggregation pheromone production have remained elusive. Studies on pheromone production in Ips spp. bark beetles have recently shown de novo biosynthesis of pheromone components via the mevalonate pathway. The gene encoding a key regulated enzyme in this pathway, 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-R), showed high transcript levels in the anterior midgut of male pine engravers, Ips pini (Say) (Coleoptera:Scolytidae). HMG-R expression in the midgut was sex, juvenile hormone, and feeding dependent, providing strong evidence that this is the site of acyclic monoterpenoid (ipsdienol) pheromone production in male beetles. Additionally, isolated midgut tissue from fed or juvenile hormone III (JH III)-treated males converted radiolabeled acetate to ipsdienol, as assayed by radio-HPLC. These data support the de novo production of this frass-associated aggregation pheromone component by the mevalonate pathway. The induction of a metazoan HMG-R in this process does not support the postulated role of microorganisms in ipsdienol production.

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

“…Northern analysis showed that GPPS is up-regulated by JH III in a dose-and time-dependent manner in male thoraces, similar to the transcriptional pattern described for other mevalonate pathway genes involved in pheromone biosynthesis (data not shown) (19,36,37). Semiquantitative RT-PCR demonstrated that the expression of GPPS was predominately localized to the anterior midgut tissue of pheromone-producing male I. pini (Fig.…”

“…Template DNA from an I. pini cDNA library in ZAP II (19) was amplified by using degenerate primers (5Ј-GTNGA-RATGYTICAYACN-3Ј; 5Ј-RTCRTCYTGIACYTGRAA-3Ј) designed to recognize E-IPPS cDNAs (30). Preliminary amplified products included a fragment corresponding to FPPS.…”

“…2). Within the first 20 amino acids, residues from the start codon is a consensus N-terminal peroxisomal targeting sequence (S 11 -L 19 ).…”

“…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.…”

An epoxide hydrolase involved in the biosynthesis of an insect sex attractant and its use to localize the production site

“…The tremendous progress of molecular methods during the past years and the availability of genome sequences of various model organisms shifted the interests of researchers more and more toward the genes involved in pheromone biosynthesis (14)(15)(16)(17)(18)(19)(20). Particularly, the use of RNA interference (RNAi)-mediated gene silencing and in situ RT-PCR has demonstrated the usefulness of these cutting edge tools for insect pheromone research, because they allow both the unequivocal assignment of gene function in vivo and cell localization of biosynthetic pathways within the organism (21)(22)(23).…”