# CYP6B Subtype Expression Fluctuates in the Great Mormon, Papilio memnon, with Changes in the Components of the Host Plants

## TL;DR

This study shows that the expression of CYP6B enzymes in Great Mormon butterfly larvae changes depending on the type of citrus host plant they feed on.

## Contribution

The study reveals a link between host plant phytochemicals and CYP6B subtype expression in swallowtail larvae.

## Key findings

- CYP6B2, CYP6B5, and CYP6B6 mRNA levels vary with the type of citrus plant fed to larvae.
- Phytochemicals in host plants influence CYP6B mRNA expression in larval fat body and midgut.
- Six CYP6B subtypes are expressed in the fat body and midgut of P. memnon larvae.

## Abstract

Papilionidae larvae metabolise host plant components using a metabolic enzyme, cytochrome P450 (CYP). However, the transcriptomic profile of the CYP6B subfamily was insufficiently studied in Rutaceae plant-fed swallowtails. In this study, CYP6B mRNA expression was investigated when feeding different kinds of Citrus plants to the Great Mormon (Papilio memnon) larvae which use a narrow range of host plants. Consequently, CYP6B2, CYP6B5, and CYP6B6 mRNA expressions were changed depending on the kind of Citrus plants provided to the larvae. Furthermore, the chemicals included in the Citrus plants fed to the larvae were different. Our study suggests that phytochemicals cause the alternation of CYP6B subtypes mRNA expression, and CYP6B contributes to metabolising phytochemicals in the host plant in P. memnon larvae. More studies about the relationship between phytochemicals and the metabolic function of CYP6B will reveal the mechanism of host plant selection in swallowtails.

Cytochrome P-450 (CYP) is one of the metabolic enzymes which is conserved among organisms to metabolise xenobiotics. The metabolic role and transcriptomic profiles of the CYP6B subfamily have been studied in some Papilionidae insects. However, the role of CYP6Bs expressed in Rutaceae plant-fed swallowtails has yet to be fully examined. Here, the expression profile of CYP6B in the Great Mormon (Papilio memnon) larvae, which prefer Citrus plants to the Rutaceae plant, was investigated by RNA sequencing analysis and real-time quantitative PCR when feeding different kinds of Citrus plants. We found that six kinds of CYP6B subtype transcripts were expressed in the larval fat body and midgut. Then, we focused on CYP6B2, CYP6B5, and CYP6B6 transcripts and examined their mRNA expression in the larvae fed on different plants. These CYP6B mRNA expressions were changed in the larval fat body and the midgut by changing the host plants. The presence of chemicals specific to each host plant was confirmed when the host plant components were examined by database, literature, and thin-layer chromatography. Our study suggests that phytochemicals in the host plant affect CYP6B subtypes mRNA expression in P. memnon larval fat body and midgut, and CYP6B subtypes may relate to metabolise the phytochemicals in the host plants.