Monoterpenoid Pheromone Production in Coleoptera: Characterization of Geranyl Diphosphate Synthase

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Insects in the order Coleoptera are among the most destructive pests in the United States. Bark beetles are responsible for losses of billions of cubic feet of coniferous standing timber each year in North America. The cotton boll weevil Anthonomas grandis accounts for over $300 million average annual yield loss and control costs. The bark beetles and the boll weevil are unique among animals in that both produce monoterpenes, C10 pheromone components that are required for mating and reproduction. The long term goal of this project is to develop new and effective pest management tactics based on insect pheromone systems. To fully exploit pheromone-mediated bark beetle and cotton boll weevil behavior from a management standpoint, a thorough understanding of the origin, expression and activity of these signals is important. Recent work in the Blomquist/Tittiger laboratory has demonstrated that the male pine engraver beetle, Ips pini, synthesizes ipsdienol de novo, and that production is controlled by juvenile hormone (JH) which induces 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-R) and HMG-CoA synthase (HMG-S) transcript levels. Another key enzyme in monoterpenoid pheromone production is geranyl diphosphate synthase (GPPS), which controls the chain length of the isoprenoid product. Work is proposed to gain an understanding of the regulation of the activity of this enzyme in relationship to pheromone production and to clone, sequence and model the enzyme. The studies outlined in this proposal are significant because of their impact on isoprenoid biochemistry and basic insect molecular biology. It is becoming clear that plant monoterpenes are synthesized entirely via the non-mevalonate pathway, making Ips spp. and A. grandis relatively novel systems for the study of the regulation of mevalonate-based monoterpenoid biosynthesis. Furthermore, there are few other insect models in which the molecular biology of isoprenyl diphosphate synthases have been studied, and none of these have involved GPPS or modeling studies. Also, none of these other models has a monoterpenoid end product that can be readily recovered in mg quantities as is the case with I. pini and A. grandis. Finally, Ips pini and A. grandis pheromone biosynthesis, and specifically the transcription of key isoprenoid enzymes, represents a non-developmental model system for the study of JH regulated gene expression. This work builds upon and expands the pioneering work on the molecular biological studies of insect pheromone regulation performed in the Blomquist/Tittiger laboratories.