Cytochrome P450 Genes Expressed in Phasmatodea Midguts

SIMPLE SUMMARY: Cytochrome P450s are a group of detoxification enzymes found in all animals. They are highly diverse, with multiple copies of different families of these genes in individual organisms, especially those that need to digest chemically-defended foods, such as toxic plants. The stick insects are a group of leaf-feeding herbivores whose diets can include toxic species, such as Eucalyptus, so this study sought to identify what groups of cytochrome P450s are expressed in the digestive tracts of six species of stick insects and how they evolved. The results show a complement of detoxification genes comparable to or slightly more limited than those of other insects, except for multiple enzymes per species in the subfamily CYP15A1, while most insects will only have one enzyme in this group. The functions of these expanded enzyme groups should be investigated further. ABSTRACT: Cytochrome P450s (CYPs) are xenobiotic detoxification genes found in most eukaryotes, and linked in insects to the tolerance of plant secondary chemicals and insecticide resistance. The number and diversity of CYP clans, families, and subfamilies that an organism produces could correlate with its dietary breadth or specialization. This study examined the CYP diversity expressed in the midguts of six species of folivorous stick insects (Phasmatodea), to identify their CYP complement and see if any CYPs correlate with diet toxicity or specialization, and see what factors influenced their evolution in this insect order. CYP genes were mined from six published Phasmatodea transcriptomes and analyzed phylogenetically. The Phasmatodea CYP complement resembles that of other insects, though with relatively low numbers, and with significant expansions in the CYP clades 6J1, 6A13/14, 4C1, and 15A1. The CYP6 group is known to be the dominant CYP family in insects, but most insects have no more than one CYP15 gene, so the function of the multiple CYP15A1 genes in Phasmatodea is unknown, with neofunctionalization following gene duplication hypothesized. No correlation was found between CYPs and diet specialization or toxicity, with some CYP clades expanding within the Phasmatodea and others likely inherited from a common ancestor.