Isolation, endocrine regulation and mRNA distribution of the 3‐hydroxy‐3‐methylglutaryl coenzyme A synthase (HMG‐S) gene from the pine engraver, Ips pini (Coleoptera: Scolytidae)

Abstract

We isolated a full-length cDNA encoding 3-hydroxy-3-methylglutaryl coenzyme A synthase (HMG-S) from the pine engraver beetle, Ips pini (Say), and examined its genomic structure. The intron-less gene has a predicted 460 amino acid cytosolic protein product with 73% identity to HMG-S from Dendroctonus jeffreyi, and high identity (58-64%) with other insect HMG-Ss. Topically applied juvenile hormone (JH) III induced HMG-S mRNA levels up to 6.5-fold in both sexes, mostly in the anterior midgut, though there were differences between males and females in the timing, sensitivity to JH III dose and tissue distribution of HMG-S mRNA. These data further validate the coordinate regulation of mevalonate pathway genes for de novo isoprenoid pheromone production in bark beetles.

Two Regulatory Mechanisms of Monoterpenoid Pheromone Production in Ips spp. Of Bark Beetles

“…The induction of mevalonate pathway genes in male bark beetles often precedes an increase in protein production, enzyme activity, and pheromone production (Tillman et al 2004;Bearfield et al 2006). In male I. confusus, either JH III treatment or feeding is sufficient to increase HMGS, HMGR, and GPPS transcript levels in the anterior midgut (Fig.…”

“…From these studies, it appears that in I. pini feeding on host phloem stimulates JH III synthesis by the corpus allatum, which, in turn, increases the expression level and enzyme activity of HMGR in the mevalonate pathway resulting in high levels of pheromone production (Tillman et al 1998). In addition, JH III also upregulates transcription of other mevalonate pathway genes, including HMG-CoA synthase (HMGS) and geranyl diphosphate synthase (GPPS), in male I. pini (Gilg et al 2005;Bearfield et al 2006;Keeling et al 2006).…”

Functional expression of a bark beetle cytochrome P450 that hydroxylates myrcene to ipsdienol

“…Pheromone-biosynthetic genes have conserved transcription profiles: they are transcribed predominantly in midguts (Tillman et al, 2004;Gilg et al, 2005;Bearfield et al, 2006); basal expression levels are higher in males than in females; and their mRNA levels are coordinately induced by feeding (Keeling et al, 2004) and topical JH III treatment . The CYP9T2 EST (IPG002G06) clusters with the EST for GPPS in microarray analyses and has 4500-fold higher basal expression levels in male midguts relative to females .…”

Iridoid biosynthesis in Chrysomelina larvae: Fat body produces early terpenoid precursors

“…Analyses of HMGR expression have been used to locate the de novo biosynthesis of monoterpenoid aggregation pheromones in male bark beetles . Increased mRNA levels of HMGR in the anterior midgut corresponded to pheromone production in males of Ips pini (Hall et al, 2002a;Nardi et al, 2002;Keeling et al, 2004Keeling et al, , 2006Tillman et al, 2004;Bearfield et al, 2006), Dendroctonus jeffreyi (Hall et al, 2002b;Tittiger et al, 2003) and Ipis paraconfusus (Ivarsson et al, 1998;Tittiger et al, 1999). In fact, scolytids have been the most studied arthropods concerning the biosynthesis of these pheromones with special emphasis on enzymes of the mevalonate pathway.…”