Terpene synthases and pathways in animals: enzymology and structural evolution in the biosynthesis of volatile infochemicals

Covering: up to the beginning of 2023 Many animals release volatile or semi-volatile terpenes as semiochemicals in intra- and inter-specific interactions. Terpenes are important constituents of pheromones and serve as chemical defenses to ward off predators. Despite the occurrence of terpene specialized metabolites from soft corals to mammals, the biosynthetic origin of these compounds has largely remained obscure. An increasing number of animal genome and transcriptome resources is facilitating the identification of enzymes and pathways that allow animals to produce terpenes independent of their food sources or microbial endosymbionts. Substantial evidence has emerged for the presence of terpene biosynthetic pathways such as in the formation of the iridoid sex pheromone nepetalactone in aphids. In addition, terpene synthase (TPS) enzymes have been discovered that are evolutionary unrelated to canonical plant and microbial TPSs and instead resemble precursor enzymes called isoprenyl diphosphate synthases (IDSs) in central terpene metabolism. Structural modifications of substrate binding motifs in canonical IDS proteins presumably facilitated the transition to TPS function at an early state in insect evolution. Other arthropods such as mites appear to have adopted their TPS genes from microbial sources via horizontal gene transfer. A similar scenario likely occurred in soft corals, where TPS families with closer resemblance to microbial TPSs have been discovered recently. Together, these findings will spur the identification of similar or still unknown enzymes in terpene biosynthesis in other lineages of animals. They will also help develop biotechnological applications for animal derived terpenes of pharmaceutical value or advance sustainable agricultural practices in pest management.