Evolution and functional divergence of enzymes involved in sesquiterpenoid hormone biosynthesis in crustaceans and insects

Juvenile hormone (JH) and methyl farnesoate (MF) play well-known roles in the development and reproduction of insects and crustaceans. Juvenile hormone acid O-methyltransferase (JHAMT) and farnesoic acid O-methyltransferase (FAMeT) are the enzymes responsible for catalyzing the biosynthesis of JH and MF, respectively. It is not clear whether the genes that encode these enzymes are present in animal lineages outside of the arthropods. Based on DNA sequence similarity, the literature suggests that an FAMeT ortholog is present in humans. However, vertebrates do not appear to produce JH or MF. To help unravel the evolution of hormonal systems in animals we have carried out the first comparative genomic analysis of JHAMT and FAMeT. We identify the first JHAMT ortholog in a crustacean genome, and FAMeT orthologs in annelid and cephalochordate genomes. Moreover, phylogenetic analyses suggest that there is no true homolog of FAMeT in humans contrary to previous hypotheses. Our analyses suggest that the presence of multiple FAMeT isoforms in arthropods may be a consequence of different evolutionary mechanisms. The genes responsible for hormone biosynthesis in extant insects and crustaceans appear to have been present at least in the Pancrustacea. Different selective forces appear to have subsequently acted on the two lineages, leading to the present functional divergence. Our use of comparative genomics and phylogenetic analysis advance knowledge of the relationships of the hormonal enzyme genes in question, and provide new insights into the evolution of hormonal systems in the largest animal phylum, the Arthropoda.