Coexpression of Three Odorant-Binding Protein Genes in the Foreleg Gustatory Sensilla of Swallowtail Butterfly Visualized by Multicolor FISH Analysis

Abstract

Lepidopteran insects are mostly monophagous or oligophagous. Female butterflies distinguish their host plants by detecting a combination of specific phytochemicals through the gustatory sensilla densely distributed on their foreleg tarsi, thereby ensuring oviposition on appropriate host plants. In this study, to gain insight into the molecular mechanism underlying host plant recognition by the gustatory sensilla, using Asian swallowtail, Papilio xuthus, we focused on a family of small soluble ligand-binding molecules, odorant-binding proteins (OBPs), and found that three OBP genes showed enriched expression in the foreleg tarsus. Multicolor fluorescence in situ hybridization analyses demonstrated the coexpression of these three OBP genes at the bases of the foreleg gustatory sensilla. Further analyses on other appendages revealed that PxutOBP3 was exclusively expressed in the tissues which could have direct contact with the leaf surface, suggesting that this OBP gene specifically plays an important role in phytochemicals perception.

Genome-Wide Analysis of Odorant-Binding Proteins in Papilio xuthus with Focus on the Perception of Two PxutGOBPs to Host Odorants and Insecticides

“…In the annotation of OBPs, a novel OBP phylogenetically close to the PBP/GOBPs clade was identified as a partial gene PxutPBP5. In previous studies, 23,25 this gene was not found but presented in our current analyses. Unfortunately, this fragmented PxutPBP5 was unable to be extended to a fulllength sequence based on genomic and transcriptomic data.…”

“…26,28 In previous studies, the OBP gene family in P. xuthus was identified based on the genome and transcriptomes. 23,25 However, functional characterization of OBPs in this species is still unknown. Our current work comprehensively reannotated the OBP gene repertoire in P. xuthus, leading to the identification of four novel genes and the revision of seven original genes, in combination with two genome assemblies and extensive transcriptome data.…”

“…Gene Identification and Nomenclature. The protein sequences of 44 OBPs previously identified in P. xuthus, 23,25 together with OBPs of B. mori, 12 S. litura, 27 D. plexippus, 20 H. melpomene, 16,21 and V. cardui, 24 were pooled into a local sequence database as queries. To exhaustively identify the genes encoding OBPs in P. xuthus, several data resources were retrieved from the National Center for Biotechnology Information (NCBI) and DNA Data Bank of Japan (DDBJ) databases, including the corresponding genomes and transcriptomes.…”

“…In a previous study, the names of 44 OBPs in P. xuthus were determined mainly based on their expression levels in foreleg tarsi. 23 To reflect the relationships of the OBP subfamilies and their physical locations on chromosomes, here we applied a new nomenclature to revise the previously described 44 OBPs. First, a Lepidoptera-specific PBP/GOBPs subclass was designated as PxutPBP1−PBP5 and PxutGOBP1−GOBP2 according to the homology with those in other lepidopterans.…”

“…Concerning the identification and expression patterns of genes, there were two relatives orthologous to GOBP1 and GOBP2 in Danaus plexippus, 20 Heliconius melpomene, 21 Pieris rapae, 22 P. xuthus, 23 and Vanessa cardui, 24 respectively. Out of the identified genes, PxutGOBP2 (previously OBP10), 23 PrapGOBP1, and PrapGOBP2 (previously named as PrapOBP1 and PrapOBP2, respectively) 22 were significantly expressed in antennae, implying their conserved functions associated with olfaction, consistent with those in moths. 13,17,18 However, to date, the functions of butterfly GOBPs remain unknown, including P. xuthus.…”