PT  - JOURNAL ARTICLE
AU  - Xiao-Qing Hou
AU  - Dan-Dan Zhang
AU  - Daniel Powell
AU  - Hong-Lei Wang
AU  - Martin N. Andersson
AU  - Christer Löfstedt
TI  - Ionotropic receptors in the turnip moth <em>Agrotis segetum</em> respond to repellent medium-chain fatty acids
AID  - 10.1101/2021.02.25.432965
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.02.25.432965
4099  - http://biorxiv.org/content/early/2021/09/04/2021.02.25.432965.short
4100  - http://biorxiv.org/content/early/2021/09/04/2021.02.25.432965.full
AB  - Background In insects, airborne chemical signals are mainly detected by two receptor families, odorant receptors (ORs) and ionotropic receptors (IRs). Functions of ORs have been intensively investigated in Diptera and Lepidoptera, while the functions and evolution of the more ancient IR family remain largely unexplored beyond Diptera.Results Here, we identified a repertoire of 26 IRs from transcriptomes of female and male antennae, and ovipositors in the moth Agrotis segetum. We observed that a large clade formed by IR75p and IR75q expansions is closely related to the acid-sensing IRs identified in Diptera. We functionally assayed each of the five AsegIRs from this clade using Xenopus oocytes and found that two receptors responded to the tested ligands. AsegIR75p.1 responded to several compounds but hexanoic acid was revealed to be the primary ligand, and AsegIR75q.1 responded primarily to octanoic acid, and less so to nonanoic acid. It has been reported that the C6-C10 medium-chain fatty acids repel various insects including many drosophilids and mosquitos. Our GC-EAD recordings showed that C6-C10 medium-chain fatty acids elicited antennal responses of both sexes of A. segetum, while only octanoic acid had repellent effect to the moths in a behavioural assay. In addition, using fluorescence in situ hybridization, we demonstrated that the five IRs and their co-receptor AsegIR8a are not located in coeloconic sensilla as found in Drosophila, but in basiconic or trichoid sensilla.Conclusions Our results significantly expand the current knowledge of the insect IR family. Based on the functional data in combination with phylogenetic analysis, we propose that subfunctionalization after gene duplication plays an important role in the evolution of ligand specificities of the acid-sensing IRs in Lepidoptera.Competing Interest StatementThe authors have declared no competing interest.