Comparison and Functional Analysis of Chemosensory Protein Genes From Eucryptorrhynchus scrobiculatus Motschulsky and Eucryptorrhynchus brandti Harold

Abstract

The tree-of-heaven root weevil (Eucryptorrhynchus scrobiculatus) and the tree-of-heaven trunk weevil (Eucryptorrhynchus brandti) are closely related species that monophagously feed on the same host plant, the Ailanthus altissima (Mill) Swingle, at different locations. However, the mechanisms of how they select different parts of the host tree are unclear. As chemosensory systems play important roles in host location and oviposition, we screened candidate chemosensory protein genes from the transcriptomes of the two weevils at different developmental stages. In this study, we identified 12 candidate chemosensory proteins (CSPs) of E. scrobiculatus and E. brandti, three EscrCSPs, and one EbraCSPs, respectively, were newly identified. The qRT-PCR results showed that EscrCSP7/8a/9 and EbraCSP7/8/9 were significantly expressed in adult antennae, while EscrCSP8a and EbraCSP8 shared low sequence identity, suggesting that they may respond to different odorant molecule binding. Additionally, EbraCSP6 and EscrCSP6 were mainly expressed in antennae and proboscises and likely participate in the process of chemoreception. The binding simulation of nine volatile compounds of the host plant to EscrCSP8a and EbraCSP8 indicated that (1R)-(+)-alpha-pinene, (–)-beta-caryophyllene, and beta-elemen have higher binding affinities with EscrCSP8a and lower affinities with EbraCSP8. In addition, there were seven, two, and one EbraCSPs mainly expressed in pupae, larvae, and eggs, respectively, indicating possible developmental-related roles in E. brandti. We screened out several olfactory-related possible CSP genes in E. brandti and E. scrobiculatus and simulated the binding model of CSPs with different compounds, providing a basis for explaining the niche differentiation of the two weevils.

Comparison of Fine Structure of the Compound Eyes in Eucryptorrhynchus scrobiculatus and Eucryptorrhynchus brandti Adults

“…Previous studies showed that the direction of numerous microvilli on the rhabdom of dorsal rim omnidia is arranged in two orthogonal directions [ 39 ]. E. scrobiculatus and E. brandti prefer light sources, and only E. scrobiculatus can perceive polarized light [ 24 ]. However, our study found that the distorted orientation of the rhabdom of E. scrobiculatus and E. brandti was not aligned in two orthogonal directions.…”

“…The selection of different wavelengths of light differs between E. scrobiculatus and E. brandti , and the attraction index of different wavelengths of light to E. scrobiculatus and E. brandti changes after light and dark treatments [ 23 ]. Both related weevils can be attracted by light, but only E. scrobiculatus can perceive polarized light [ 24 ]. We hypothesize that the differentiation of ecological niches between E. scrobiculatus and E. brandti might be related to variation in the structure of the visual organ.…”

Comparison and Functional Analysis of Odorant-Binding Proteins and Chemosensory Proteins in Two Closely Related Thrips Species, Frankliniella occidentalis and Frankliniella intonsa (Thysanoptera: Thripidae) Based on Antennal Transcriptome Analysis

“…In two closely related Anastrepha fruit flies, A. fraterculus and A. obliqua, a comparison of OBP genes between the two species revealed four genes associated with positive selection which might precede the speciation of these two species; in addition, several amino acid changes between homologous genes might be related to different host preferences [8]. Comparison and functional analysis of CSP genes from two closely related weevils, Eucryptorrhynchus scrobiculatus and E. brandti, found candidate genes that might explain the niche differentiation of the two weevils [29]. Analysis of Drosophila suzukii chemoreceptors together with nine melanogaster group members, including two of its closely related species (D. biarmipes and D. takahashii), revealed several candidate receptors associated with the ecological niche adaptation of D. suzukii [32].…”

“…However, ligand binding by OBPs seems to vary among insect species, presenting specific features depending on the species studied [25]. Molecular docking is a widely used virtual method for the prediction of the best ligands for insect OBPs [28], which has been also used for ligand binding prediction in CSPs [29]. This computational method is becoming a very important tool in screening for potential semiochemicals of given soluble olfactory proteins, as well as potential target soluble olfactory proteins of given ligands [30,31].…”

“…It has been reported that comparative analysis of chemosensory genes (OBPs, CSPs, or ORs) among closely related species could help understand the adaptation of insects to different ecological niches and their evolutionary relationships [8,29,32,33]. In two closely related Anastrepha fruit flies, A. fraterculus and A. obliqua, a comparison of OBP genes between the two species revealed four genes associated with positive selection which might precede the speciation of these two species; in addition, several amino acid changes between homologous genes might be related to different host preferences [8].…”