De novo formation of an aggregation pheromone precursor by an isoprenyl diphosphate synthase-related terpene synthase in the harlequin bug.

Abstract

Insects use a diverse array of specialized terpene metabolites as pheromones in intraspecific interactions. In contrast to plants and microbes, which employ enzymes called terpene synthases (TPSs) to synthesize terpene metabolites, limited information from few species is available about the enzymatic mechanisms underlying terpene pheromone biosynthesis in insects. Several stink bugs (Hemiptera: Pentatomidae), among them severe agricultural pests, release 15-carbon sesquiterpenes with a bisabolene skeleton as sex or aggregation pheromones. The harlequin bug, <i>Murgantia histrionica</i>, a specialist pest of crucifers, uses two stereoisomers of 10,11-epoxy-1-bisabolen-3-ol as a male-released aggregation pheromone called murgantiol. We show that <i>Mh</i>TPS (<i>Mh</i>IDS-1), an enzyme unrelated to plant and microbial TPSs but with similarity to <i>trans</i>-isoprenyl diphosphate synthases (IDS) of the core terpene biosynthetic pathway, catalyzes the formation of (1<i>S</i>,6<i>S</i>,7<i>R</i>)-1,10-bisaboladien-1-ol (sesquipiperitol) as a terpene intermediate in murgantiol biosynthesis. Sesquipiperitol, a so-far-unknown compound in animals, also occurs in plants, indicating convergent evolution in the biosynthesis of this sesquiterpene. RNAi-mediated knockdown of <i>MhTPS</i> mRNA confirmed the role of <i>MhTPS</i> in murgantiol biosynthesis. <i>Mh</i>TPS expression is highly specific to tissues lining the cuticle of the abdominal sternites of mature males. Phylogenetic analysis suggests that <i>Mh</i>TPS is derived from a <i>trans</i>-IDS progenitor and diverged from bona fide <i>trans</i>-IDS proteins including <i>Mh</i>IDS-2, which functions as an (<i>E</i>,<i>E</i>)-farnesyl diphosphate (FPP) synthase. Structure-guided mutagenesis revealed several residues critical to <i>Mh</i>TPS and <i>Mh</i>FPPS activity. The emergence of an IDS-like protein with TPS activity in <i>M. histrionica</i> demonstrates that de novo terpene biosynthesis evolved in the Hemiptera in an adaptation for intraspecific communication.