Molecular characterization and functional analysis of pheromone binding proteins and general odorant binding proteins from Carposina sasakii Matsumura (Lepidoptera: Carposinidae)

Binding characteristics and structural dynamics of two general odorant-binding proteins with plant volatiles in the olfactory recognition of Glyphodes pyloalis

Glyphodes pyloalis Walker (Lepidoptera: Pyralidae) is the most destructive pest, causing severe damage to mulberry production in China's sericulture industry. The insecticide application in mulberry orchards poses a significant risk of poisoning to Bombyx mori. Shifting from insecticides to odor attractants is a beneficial alternative, but not much data is available on the olfactory system of G. pyloalis. We identified 114 chemosensory genes from the antennal transcriptome database of G. pyloalis, with 18 odorant-binding protein (OBP) and 17 chemosensory protein (CSP) genes significantly expressed in the antennae. Ligand-binding assays for two antennae-biased expressed general odorant-binding proteins (GOBPs) showed high binding affinities of GOBP1 to hexadecanal, β-ionone, and 2-ethylhexyl acrylate, while GOBP2 exhibited binding to 4-tert-octylphenol, benzyl benzoate, β-ionone, and farnesol. Computational simulations indicated that van der Waal forces predominantly contributed to the binding free energy in the binding processes of complexes. Among them, Phe12 of GOBP1 and Phe19 of GOBP2 were demonstrated to play crucial roles in their bindings to plant volatiles using site-directed mutagenesis experiments. Moreover, hexadecanal and β-ionone attracted G. pyloalis male moths in the behavioral assays, while none of the candidate plant volatiles significantly affected female moths. Our findings provide a comprehensive understanding of the molecular mechanisms underlying olfactory recognition in G. pyloalis, setting the groundwork for novel mulberry pests control strategies based on insect olfaction.

EsigPBP3 Was the Important Pheromone-Binding Protein to Recognize Male Pheromones and Key Eucalyptus Volatiles

Pheromone-binding proteins (PBPs) are specific odorant-binding proteins that can specifically recognize insect pheromones. Through transcriptional analysis of the antennae of adult Endoclita signifer, EsigPBP3 was discovered and identified, and EsigPBP3 was found to be highly expressed in the antennae of male moths. Based on the binding characteristics and ability of EsigPBP3, we can find the key ligands and binding site to consider as a target to control the key wood bore E. signifier. In this study, the fluorescence competitive binding assays (FCBA) showed that EsigPBP3 had a high binding affinity for seven key eucalyptus volatiles. Molecular docking analysis revealed that EsigPBP3 had the strongest binding affinity for the sexual pheromone component, (3E,7E)-4,7,11-trimethyl-1,3,7,10-dodecatetraene. Furthermore, same as the result of FCBA, the EsigPBP3 exhibited high binding affinities to key eucalyptus volatiles, eucalyptol, α-terpinene, (E)-beta-ocimene, (-)-β-pinene, and (-)-α-pinene, and PHE35, MET7, VAL10, PHE38, ILE52, and PHE118 are key sites. In summary, EsigPBP3 exhibits high binding affinity to male pheromones and key volatile compounds and the crucial binding sites PHE35, MET7, VAL10, PHE38, ILE52, and PHE118 can act as targets in the recognition of E. signifier pheromones.

Transcriptome analysis and expression profiles of odorant binding proteins and chemosensory proteins in Orius sauteri

The flower bug Orius sauteri (Heteroptera: Anthocoridae), is a polyphagous predator and a natural enemy widely used in biological pest control to micro-pests including aphids, spider mites, thrips and so on. In the present study, the transcriptome analysis of adult heads in O. sauteri were performed and identified a total of 38 chemosensory genes including 24 odorant binding proteins (OBPs) and 14 chemosensory proteins (CSPs). Subsequently, we conducted quantitative real-time PCR to detect the tissue expression level of 18 OBPs and 8 CSPs. The results showed that almost all OsauOBPs and OsauCSPs have a high expression level in the adult heads of both sexes. In addition, 5 OsauOBPs (OBP1, OBP2, OBP3, OBP4 and OBP14) have a significantly higher expressed in male heads than female, indicating that these chemosensory proteins might be involved in the male-specific behaviors such as pheromone reception and mate-seeking. This study will provide helpful reference for subsequent understanding of chemoreception mechanism in O. sauteri.

The binding affinity of two general odorant binding proteins in Spodoptera frugiperda to general volatiles and insecticides

Spodoptera frugiperda is a kind of polyphagous pest, and can damage a large number different host plants around the worldwide. The molecular mechanisms of two general odorant binding proteins (GOBPs) binding with general volatiles and insecticides are still blank. In this study, we investigated the function of two GOBPs in S. frugiperda, by expressing two SfruGOBPs and tested the binding affinities by the fluorescence competition binding assays. The results exhibited that SfruGOBP1 has binding affinities to 4 of 38 general volatiles and 3 of 7 insecticides. In contrast, SfruGOBP2 showed a broader ligand-binding spectrum to 21 volatiles and 4 insecticides, suggesting SfruGOBP2 may plays a more important role in perceiving host volatiles than SfruGOBP1. Furthermore, we used molecular docking and site-directed mutagenesis assay to explored the key amino acid residues of two SfruGOBP to insecticides ligand. This study provides some valuable information to exploring the olfactory mechanism of two GOBPs bound the host plant volatiles and insecticides in S. frugiperda.

Antennal transcriptome analysis of odorant-binding proteins and characterization of GOBP2 in the variegated cutworm Peridroma saucia

Odorant-binding proteins (OBPs) are expressed at extremely high concentrations in the chemo-sensilla lymph of insects and have long been thought to be crucial for delivering the semiochemicals to the odorant receptors. They are represented by multiple classes: general odorant-binding proteins (GOBP1 and GOBP2) and pheromone-binding proteins. In the current study, we identified a total of 35 OBPs in the antennal transcriptome of Peridroma saucia, a worldwide pest that causes serious damage to various crops. A gene expression value (TPM, transcripts per million) analysis revealed that seven OBPs (PsauPBP1/2/3, PsauGOBP1/2, PsauOBP6, and PsauOBP8) were highly abundant in the antennae. Next, we focused on the expression and functional characterization of PsauGOBP2. Real-time quantitative-PCR analysis demonstrated that PsauGOBP2 was predominantly expressed in the antennae of both sexes. Fluorescence binding assays showed that the recombinant PsauGOBP2 strongly binds to the female sex pheromone components Z11-16: Ac (Ki = 4.2 μM) and Z9-14: Ac (Ki = 4.9 μM) and binds moderately (6 µM ≤ Ki ≤ 13 µM) to the host plant volatiles phenylethyl acetate, β-myrcene, and dodecanol. Further 3D structural modeling and molecular docking revealed that several crucial amino acid residues are involved in ligand binding. The results not only increase our understanding of the olfactory system of P. saucia but also provide insights into the function of PsauGOBP2 that has implications for developing sustainable approaches for P. saucia management.

Functional differentiation of two general-odorant binding proteins in Hyphantria cunea (Drury) (Lepidoptera: Erebidae)

BACKGROUND

General odor-binding proteins (GOBPs) play critical roles in insect olfactory recognition of sex pheromones and plant volatiles. Therefore, the identification of GOBPs in Hyphantria cunea (Drury) based on their characterization to pheromone components and plant volatiles is remain unknown.

RESULTS

In this study, two H. cunea (HcunGOBPs) genes were cloned, and their expression profiles and odorant binding characteristics were systematically analyzed. Firstly, the tissue expression study showed that both HcunGOBP1 and HcunGOBP2 were highly expressed in the antennae of both sexes, indicating their potential involvement in the perception of sex pheromones. Secondly, these two HcunGOBPs genes were expressed in Escherichia coli and ligand binding assays were used to assess the binding affinities to its sex pheromone components including two aldehydes and two epoxides, and some plant volatiles. HcunGOBP2 showed high binding affinities to two aldehyde components (Z9, Z12, Z15-18Ald and Z9, Z12-18Ald), and showed low binding affinities to two epoxide components (1, Z3, Z6-9S, 10R-epoxy-21Hy and Z3, Z6-9S, 10R-epoxy-21Hy), whereas HcunGOBP1 showed weak but significant binding to all four sex pheromone components. Furthermore, both HcunGOBPs demonstrated variable binding affinities to the plant volatiles tested. Thirdly, in silico studies of HcunGOBPs utilized homology, structure modeling, and molecular docking revealed critical hydrophobic residues might be involved in the binding of HcunGOBPs to their sex pheromone components and plant volatiles.

CONCLUSION

Our study suggests that these two HcunGOBPs may serve as potential targets for future studies of HcunGOBPs ligand binding, providing insight in the mechanism of olfaction in H. cunea. © 2023 Society of Chemical Industry.

Identification and Functional Characterization of General Odorant Binding Proteins in Orthaga achatina

The olfactory system in insects are crucial for recognition of host plants and oviposition sites. General odorant binding proteins (GOBPs) are thought to be involved in detecting odorants released by host plants. Orthaga achatina (Lepidoptera: Pyralidae) is one of the most serious pests of camphor trees, Cinnamomum camphora (L.) Presl, an important urban tree species in southern China. In this study, we study the GOBPs of O. achatina. Firstly, two full-length GOBP genes (OachGOBP1 and OachGOBP2) were successfully cloned according to transcriptome sequencing results, and real-time quantitative PCR measurements showed that both GOBP genes were specifically expressed in the antennae of both sexes, proposing their important roles in olfaction. Then, both GOBP genes were heterologous expressed in Escherichia coli and fluorescence competitive binding assays were conducted. The results showed that OachGOBP1 could bind Farnesol (K_i = 9.49 μM) and Z11-16: OH (K_i = 1.57 μM). OachGOBP2 has a high binding affinity with two camphor plant volatiles (Farnesol, K_i = 7.33 μM; α-Phellandrene, K_i = 8.71 μM) and two sex pheromone components (Z11-16: OAc, K_i = 2.84 μM; Z11-16: OH, K_i = 3.30 μM). These results indicate that OachGOBP1 and OachGOBP2 differ in terms of odorants and other ligands. Furthermore, key amino acid residues that bind to plant volatiles were identified in GOBPs using 3-D structure modeling and ligand molecular docking, predicting the interactions between the GOBPs and the host plant volatiles.

Functional disparity of four pheromone-binding proteins from the plum fruit moth Grapholita funebrana Treitscheke in detection of sex pheromone components

Grapholita funebrana, also known as the plum fruit moth, is an oligophagous pest species that causes enormous economic losses of the fruits of Rosaceae. An eco-friendly method for the control of G. funebrana besides chemical control has not yet been developed. The sex pheromone communication system plays an important role in moth courtship and mating, in which pheromone-binding proteins (PBPs) are critical. In this research, we identified four PBPs, namely, GfunPBP1.1, GfunPBP1.2, GfunPBP2, and GfunPBP3, from the antennae of G. funebrana. The results of real-time quantitative PCR (RT-qPCR) showed that all four GfunPBPs were overwhelmingly expressed in the antennae and that GfunPBP1.2 and GfunPBP2 showed male-biased expression patterns, whereas GfunPBP1.1 and GfunPBP3 were equally expressed between sexes. The results of ligand-binding assays illustrated that although all four recombinant GfunPBPs (rGfunPBPs) had binding activity with the tested sex pheromone compounds, their preferred ligands were significantly different. rGfunPBP2 had the strongest binding affinity to Z8-12:Ac and Z8-12:OH; rGfunPBP1.1 preferred to bind Z8-14:Ac, Z10-14:Ac, and 12:OH more than to the other three GfunPBPs; and rGfunPBP1.2 exhibited stronger binding affinity to E8-12:Ac than to the other rGfunPBPs. Molecular docking results demonstrated that hydrophobic forces, especially van der Waals forces and hydrogen bonds, were the most important forces that maintained GfunPBP-pheromone ligand complexes. This study will improve our understanding of the sex pheromone recognition mechanisms of G. funebrana and promote the development of novel strategies for controlling G. funebrana.

Molecular Characterization and Expression Patterns of Two Pheromone-Binding Proteins from the Diurnal Moth Phauda flammans (Walker) (Lepidoptera: Zygaenoidea: Phaudidae)

Sex pheromone-binding proteins (PBPs) play an important role in sex pheromone recognition in Lepidoptera. However, the mechanisms of chemical communication mediating the response to sex pheromones remain unclear in the diurnal moths of the superfamily Zygaenoidea. In this study, Phauda flammans (Walker) (Lepidoptera: Zygaenoidea: Phaudidae) was used as a model insect to explore the molecular mechanism of sex pheromone perception in the superfamily Zygaenoidea. Two novel pheromone-binding proteins (PflaPBP1 and PflaPBP2) from P. flammans were identified. The two pheromone-binding proteins were predominantly expressed in the antennae of P. flammans male and female moths, in which PflaPBP1 had stronger binding affinity to the female sex pheromones Z-9-hexadecenal and (Z, Z, Z)-9, 12, 15-octadecatrienal, PflaPBP2 had stronger binding affinity only for (Z, Z, Z)-9, 12, 15-octadecatrienal, and no apparent binding affinity to Z-9-hexadecenal. The molecular docking results indicated that Ile 170 and Leu 169 are predicted to be important in the binding of the sex pheromone to PflaPBP1 and PflaPBP2. We concluded that PflaPBP1 and PflaPBP2 may be responsible for the recognition of two sex pheromone components and may function differently in female and male P. flammans. These results provide a foundation for the development of pest control by exploring sex pheromone blocking agents and the application of sex pheromones and their analogs for insect pests in the superfamily Zygaenoidea.

Gut bacteria induce oviposition preference through ovipositor recognition in fruit fly

Gut bacteria play important roles in insect life cycle, and various routes can be used by insects to effectively transmit their gut bacteria. However, it is unclear if the gut bacteria can spread by actively attracting their insect hosts, and the recognition mechanisms of host insects are poorly understood. Here, we explore chemical interactions between Bactrocera dorsalis and its gut bacterium Citrobacter sp. (CF-BD). We found that CF-BD could affect the development of host ovaries and could be vertically transmitted via host oviposition. CF-BD could attract B. dorsalis to lay eggs by producing 3-hexenyl acetate (3-HA) in fruits that were hosts of B. dorsalis. Furthermore, we found that B. dorsalis could directly recognize CF-BD in fruits with their ovipositors in which olfactory genes were expressed to bind 3-HA. This work reports an important mechanism concerning the active spread of gut bacteria in their host insects.

Ligand-binding specificities of four odorant-binding proteins in Conogethes punctiferalis

Odorant-binding proteins (OBPs) play essential roles in lepidopteran insects' perception of host volatiles by binding and transporting hydrophobic ligands. The yellow peach moth (YPM), Conogethes punctiferalis (Guenée), is a serious agricultural pest, with broad host range and cryptic feeding habits. However, few studies about YPM perceiving pheromones and host plant odorants have been reported. In this study, four OBP genes (CpunOBP8, CpunOBP9, CpunABP, and CpunGOBP2) were cloned from the antennae of YPM. The recombinant proteins were expressed and purified by prokaryotic expression system, with their binding affinities to 26 ligands being tested. Four CpunOBPs all had six conserved cysteine residues, which were typical structural characteristics of classical OBPs. The fluorescence competitive binding assay indicated that CpunOBP8 and CpunABP could not only exhibit high binding affinities to female sex pheromones, but also to host plant odorants. For example, CpunOBP8 bound strongly with cis-10-hexadecenal, hexadecanal, and so forth, whereas CpunABP bound with cis-10-hexadecenal, camphene, and 3-carene. Comparatively, CpunOBP9 and CpunGOBP2 could only bind with host plant odorants, with CpunOBP9 binding strongly to 3-methyl-1-butanol, hexyl acetate, and so forth, while CpunGOBP2 displaying the widest binding spectra and correlating with 3-carene, pentyl acetate, and so forth. The results indicated that on the one hand, each of the four CpunOBPs had its specific binding spectra when binding and transporting olfactory ligands; on the other hand, the same ligand might be bound to more than one CpunOBPs, which would provide information for the potential application of semiochemicals in controlling YPM.

EsigGOBP1: The Key Protein Binding Alpha-Phellandrene in Endoclita signifer Larvae

Endoclita signifer larvae show olfactory recognition towards volatiles of eucalyptus trunks and humus soils. Further, EsigGOBP1 was identified through larval head transcriptome and speculated as the main odorant-binding proteins in E. signifer larvae. In this study, the highest expression of EsigGOBP1 was only expressed in the heads of 3rd instar larvae of E. signifer, compared with the thorax and abdomen; this was consistent with the phenomenon of habitat transfer of 3rd instar larvae, indicating that EsigGOBP1 was a key OBP gene in E. signifer larvae. Results of fluorescence competition binding assays (FCBA) showed that EsigGOBP1 had high binding affinities to eight GC-EAD active ligands. Furthermore, screening of key active odorants for EsigGOBP1 and molecular docking analysis, indicated that EsigGOBP1 showed high binding activity to alpha-phellandrene in 3rd instar larvae of E. signifer. Conformational analysis of the EsigGOBP1-alpha-phellandrene complex, showed that MET49 and GLU38 were the key sites involved in binding. These results demonstrated that EsigGOBP1 is a key odorant-binding protein in E. signifer larvae, which recognizes and transports eight key volatiles from eucalyptus trunk, especially the main eucalyptus trunks volatile, alpha-phellandrene. Taken together, our results showed that EsigGOBP1 is involved in host selection of E. signifer larvae, which would aid in developing EsigGOBP1 as molecular targets for controlling pests at the larval stage.

Different Binding Affinities of Three General Odorant-Binding Proteins in Grapholita funebrana (Treitscheke) (Lepidoptera: Tortricidae) to Sex Pheromones, Host Plant Volatiles, and Insecticides

Insect general odorant-binding proteins (GOBPs) play irreplaceable roles in filtering, binding, and transporting host odorants to olfactory receptors. Grapholita funebrana (Treitscheke) (Lepidoptera: Tortricidae), an economically important pest of fruit crops, uses fruit volatiles as cues to locate host plants. However, the functions of GOBPs in G. funebrana are still unknown. Three GOBP genes, namely, GfunGOBP1, GfunGOBP2, and GfunGOBP3, were cloned, and their expression profiles in different tissues were detected by the method of real-time quantitative PCR (RT-qPCR). The binding properties of recombinant GfunGOBPs (rGfunGOBPs) to various ligands were investigated via fluorescence binding assays. The three GfunGOBPs were mainly expressed in the antennae of both male and female moths. All these three rGfunGOBPs could bind to sex pheromones, while having varying affinities toward these pheromones. The three rGfunGOBPs also displayed a wide range of ligand-binding spectrums with tested host odorants. The rGfunGOBP1, rGfunGOBP2, and rGfunGOBP3 bound to 34, 33, and 30 out of the 41 tested odorants, respectively. Three rGfunGOBPs had overlapping binding activities to β-myrcene, (-)-α-phellandrene, and ethyl isovalerate with the Ki less than 3.0 μM. The rGfunGOBP1 and rGfunGOBP3 could selectively bind to several insecticides, whereas rGfunGOBP2 could not. Three rGfunGOBPs had the dual functions of selectively binding to sex pheromones and host odorants. Moreover, the rGfunGOBP1 and rGfunGOBP3 can also serve as 'signal proteins' and bind to different insecticides. This study contributed to elucidating the potential molecular mechanism of the olfaction for G. funebrana, and thereby promotes the development of effective botanical attractants or pheromone synergists to control G. funebrana.

The Adelphocoris lineolatus OBP4: Support for evolutionary and functional divergence of a mirid pheromone-binding protein from that found in lepidopteran moths

Pheromone-binding proteins (PBPs) have been extensively investigated in lepidopteran moths, but their evolution and function in hemipteran species remain unclear. Our previous study demonstrated that an odorant-binding protein, OBP4, of the mirid bug Adelphocoris lineolatus functions as a candidate hemipteran PBP but clustered with lepidopteran antennae-binding proteins (ABPs) rather than in the PBP/general odorant-binding protein (GOBP) clade. In this study, we hypothesized that origin and function of PBPs in hemipteran bugs may differ from those of lepidopteran moths. To test this hypothesis, we first constructed a phylogenetic tree using insect OBPs from sister hemipteran and holometabolous lineages, and the results indicated that neither OBP4 nor other types of candidate PBPs of mirid bugs clustered with the lepidopteran PBP/GOBP clade. Then, a fluorescence competitive binding assay was employed to determine binding affinities of recombinant OBP4 protein to host plant volatiles, with functional groups different from A. lineolatus sex pheromone components. The results revealed that OBP4 highly bound the female adult attractant 3-hexanone and 15 other mirid bug biologically active plant volatiles. Finally, we examined cellular expression profiles of OBP4 in putative antennal sensilla that are related to female A. lineolatus host plant location. The fluorescence in situ hybridization and immunocytochemical labeling assay showed that the OBP4 gene was highly expressed in the multiporous olfactory sensilla medium-long sensilla basiconica rather than in the short sensilla basiconica or uniporous sensilla chaetica. These results, together with those of our previous studies, indicate that OBP4 not only functions in recognition of bug-produced sex pheromones in males, but is probably involved in detection of host plant volatiles in both A. lineolatus sexes. Our findings support the hypothesis that the origin and function of PBPs in hemipteran bugs differ from those of well-known PBPs in lepidopteran moths, which provides a novel perspective on evolutionary mechanisms of sex pheromone communication across insect orders.

GOBP1 from the Variegated Cutworm Peridroma saucia (Hübner) (Lepidoptera: Noctuidae) Displays High Binding Affinities to the Behavioral Attractant (Z)-3-Hexenyl acetate

The variegated cutworm Peridroma saucia (Hübner) is a worldwide pest that causes serious damage to many crops. To recognize sex pheromones and host plant volatiles, insects depend on olfactory chemoreception involving general odorant-binding proteins (GOBPs). In this study, PsauGOBP1 was cloned from the adult antennae of P. saucia. RT-qPCR and Western-blot analysis showed that PsauGOBP1 was specifically and equally expressed in the adult antennae of both females and males. Fluorescence competitive-binding assays with sex pheromones and host plant volatiles demonstrated that PsauGOBP1 bound to six host plant volatiles: (Z)-3-hexenyl acetate (K_D = 4.0 ± 0.1 μM), citral (K_D = 5.6 ± 0.4 μM), farnesol (K_D = 6.4 ± 0.6 μM), nonanal (K_D = 6.8 ± 0.3 μM), (Z)-3-hexen-1-ol (K_D = 8.5 ± 0.6 μM), and benzaldehyde (K_D = 9.4 ± 0.5 μM). Electroantennogram recordings with the six host plant volatiles indicated that (Z)-3-hexenyl acetate elicited the strongest responses from both male and female antennae. Further bioassays using Y-tube olfactometers showed that (Z)-3-hexenyl acetate was attractive to adult P. saucia of both sexes. These results suggest that PsauGOBP1 might be involved in detecting host plant volatiles and that (Z)-3-hexenyl acetate might serve as a potential attractant for the biological control of P. saucia.

Identification of the differences in olfactory system between male and female oriental tobacco budworm Helicoverpa assulta

The olfactory system of insects facilitates their search for host and mates, hence it plays an essential role for insect survival and reproduction. Insects recognize odor substances through olfactory neurons and olfactory genes. Previous studies showed that there are significant sex-specific differences in how insects identify odorant substances, especially sex pheromones. However, whether the sex-specific recognition of odorant substances is caused by differences in the expression of olfaction-related genes between males and females remains unclear. To clarify this problem, the whole transcriptome sequence of the adult Helicoverpa assulta, an important agricultural pest of tobacco and other Solanaceae plants, was obtained using Pacbio sequencing. RNA-seq analysis showed that there were 27 odorant binding proteins (OBPs), 24 chemosensory proteins, 4 pheromone-binding proteins (PBPs), 68 odorant receptors and 2 sensory neuron membrane proteins (SNMPs) genes, that were expressed in the antennae of male and female H. assulta. Females had significantly higher expression of General odorant-binding protein 1-like, OBP, OBP3, PBP3 and SNMP1 than males, while males had significantly higher expression of GOBP1, OBP7, OBP13, PBP2 and SNMP2. These results improve our understanding of mate search and host differentiation in H. assulta.

Discovery of behaviorally active semiochemicals in Aenasius bambawalei using a reverse chemical ecology approach

BACKGROUND

The invasive mealybug, Phenacoccus solenopsis, has caused serious damage to cotton crops throughout the world. Aenasius bambawalei is a dominant endoparasitoid of P. solenopsis. Exploration of behaviorally active semiochemicals may promote the efficacy of parasitoids used in biological control. Reverse chemical ecology, based on the physiological function of odorant-binding proteins (OBPs), provides an effective approach to screen behaviorally active compounds to target insect pests. Determination of the binding mechanisms and specificity towards different odorants in A. bambawalei may facilitate the development of more-efficient biological control strategies.

RESULTS

We characterized the expression profile and analyzed the binding affinity of OBP28 in A. bambawalei. AbamOBP28 showed high expression in the wings and antennae of both male and female A. bambawalei. A fluorescence competitive binding assay indicated that AbamOBP28 displayed strong binding affinity to most candidate ligands. Circular dichroism spectra demonstrated that 1-octen-3-one, myrcene, dodecane, 2,4,4-trimethyl-2-pentene, nonanal, and limonene elicited conformational changes in AbamOBP28. Electrophysiological and behavioral bioassays revealed that diethyl sebacate, 2,4,4-trimethyl-2-pentene, and 1-octen-3-one evoked significant electroantennography responses and functioned as attractants in A. bambawalei at specific concentrations. Furthermore, three-dimensional structure modeling and molecular docking showed that hydrogen bonds were formed by Glu1 and Ser75 of AbamOBP28 with diethyl sebacate, respectively.

CONCLUSION

These results demonstrate that AbamOBP28 is involved in the chemoreception of A. bambawalei. The identified protein provides a potential target for efficient enemy utilization and pest control, and the overall results may help develop protocols for more effective screening of behaviorally active semiochemicals. © 2021 Society of Chemical Industry.

Characterization of the binding ability of the odorant binding protein BminOBP9 of Bactrocera minax to citrus volatiles

BACKGROUND

Bactrocera minax, one of the most important citrus pests, oviposits exclusively on citrus fruit. In the insect olfactory system, odorant-binding proteins (OBPs) facilitate the initial recognition role of host odor molecules. The aim of this study was to characterize the functional OBPs of B. minax and identify specific volatile organic compounds in the Citrus genus as OBP targets.

RESULTS

BminOBP9 (BminGOBP99a), a closely related homolog of BdorGOBP99a, which reduces the egg-laying behavior of Bactrocera dorsalis through silencing technology, was cloned, expressed, and purified. The binding ability of BminOBP9 to 11 citrus volatiles was then examined using fluorescence competition binding assays (FCBA). The results demonstrated that BminOBP9 could bind to all tested citrus volatiles, as could BdorGOBP99a, ZcucGOBP99a, and ZtauGOBP99a. Interestingly, the binding ability of BminOBP9 was the strongest among the four, suggesting that BminOBP9 may have a function in the specific recognition of citrus volatiles. Furthermore, we aligned the above four proteins and found nine distinctive amino acid sites in BminOBP9. To identify the unique binding sites of BminOBP9, we produced the nine mutants using site-directed mutagenesis. Further FCBA showed that the binding ability of the nine mutants to citrus volatiles significantly reduced, and six of them (substitutes S24P, L36F, E53K, N68D, D112A, and S118R) had the weakest binding ability.

CONCLUSION

The results demonstrated that BminOBP9 was the specific protein involved in the perception of citrus host volatiles by B. minax. Moreover, BminOBP9 could prove efficient in screening the candidate odors for pest management. © 2020 Society of Chemical Industry.

Functional Characterization of Chemosensory Protein AmalCSP5 From Apple Buprestid Beetle, Agrilus mali (Coleoptera: Buprestidae)

In the sensitive and complex chemo-sensation system of insects, chemosensory proteins (CSPs) can facilitate the transfer of chemical information and play important roles for variable behaviors of insects. We cloned the chemosensory protein AmalCSP5 from antennae of the apple buprestid beetle (Agrilus mali Matsumura), a serious invasive pest of wild apple trees. Expression profiling showed that AmalCSP5 was expressed in various tissues, suggesting its significance in multiple physiological activities and behaviors of A. mali. AmalCSP5 was preferentially expressed in female antennae and male abdomens. AmalCSP5 was able to bind a variety of test volatiles, especially alcohols and esters. AmalCSP5 exhibited good binding affinity for all five test secondary compounds (i.e., procyanidin, phlorizin, kaemferol, chlorogenic acid, and rutin), suggesting its preferential binding abilities to nonvolatile host plant secondary metabolites and critical roles in gustatory perception of nonvolatiles. Tyr27 and Ser69 of AmalCSP5 could form hydrogen bonds with hexyl benzoate and hexyl hexanoate, respectively. Procyanidin, the best ligand among all test compounds, could form hydrogen bonds with three amino acid residues (i.e., Arg7, Leu8, and Lys41) of AmalCSP5. Thus, high ligand binding affinity for AmalCSP5 seemed to be dependent mainly on the formation of hydrogen bonds. The putative key amino acid residues of AmalCSP5 can be used as molecular targets for designing and screening new attractants and repellents for A. mali. Our results provide insights into binding interactions of AmalCSP5 with volatile and nonvolatile ligands, and a firm basis for developing eco-friendly management strategies of A. mali.

Functional Disparity of Three Pheromone-Binding Proteins to Different Sex Pheromone Components in Hyphantria cunea (Drury)

Hyphantria cunea (Drury) is a destructive invasive pest species in China that uses type II sex pheromone components. To date, however, the binding mechanisms of its sex pheromone components to their respective pheromone-binding proteins (HcunPBPs 1/2/3) have not been explored. In the current study, all three HcunPBPs were expressed in the antennae of both sexes. The prokaryotic expression and ligand binding assays were employed to study the binding of the moth's four sex pheromone components, including two aldehydes and two epoxides, and 24 plant volatiles to the HcunPBPs. Our results showed that the abilities of these HcunPBPs to bind to the aldehydes were significantly different from binding to the epoxides. These three HcunPBPs also selectively bind to some of the plant volatiles tested. Our molecular docking results indicated that some crucial hydrophobic residues might play a role in the binding of HcunPBPs to their sex pheromone components. Three HcunPBPs have different selectivities for pheromone components with both major and minor structural differences. Our study provides a fundamental insight into the olfactory mechanism of moths at the molecular level, especially for moth species that use various type II pheromone components.

Identification of cytochrome P450, odorant-binding protein, and chemosensory protein genes involved in Type II sex pheromone biosynthesis and transportation in the tea pest, Scopula subpunctaria

Sex pheromone-based pest management technology has been widely used to monitor and control insect pests in the agricultural, forestry, and public health sectors. Scopula subpunctaria is a widespread tea pest in China with Type II sex pheromone components. However, limited information is available on the biosynthesis and transportation of Type II sex pheromone components. In this study, we constructed an S. subpunctaria sex pheromone gland (PG) transcriptome and obtained 85,246 transcripts. Cytochrome P450 monooxygenases (CYPs) thought to epoxidize dienes and trienes to epoxides in the PG and odorant-binding proteins (OBPs) and chemosensory genes (CSPs) thought to be responsible for the binding and transportation of sex pheromone components. In present study, a total of 79 CYPs, 29 OBPs and 17 CSPs were identified. We found that SsubCYP341A and SsubCYP341B_ortholog1 belonged to the CYP341 family and were more highly expressed in the PG than in the female body. Of these, SsubCYP341A was the seventh-most PG-enriched CYP in the PG transcriptome. Two CYP4 members, CYP340BD_ortholog2 and CYP4G, were the top two most PG-enriched CYPs. Tissue expression and phylogenetic tree analysis showed that SsubOBP25, 27, and 28 belonged to the moth pheromone-binding protein family; they were distinctly expressed in the antennae and were more abundant in male antennae than in female antennae. SsubCSP16 was distributed into the same clade as CSPs from other moths that showed high binding affinities to sex pheromone components. It indicated that all the above-mentioned genes could be involved in sex pheromone biosynthesis or transportation. Our study provides large-scale PG sequence information that can be used to identify potential targets for the biological control of S. subpunctaria by disrupting its sex pheromone biosynthesis and transportation pathways.

CcOBP2 plays a crucial role in 3-carene olfactory response of the parasitoid wasp Chouioia cunea

Chouioia cunea (Yang) is a pupal parasitoid wasp and this species is able to seek host insects depending on its olfactory system. However, the molecular mechanism of the olfactory system in the C. cunea is still limited. To identify putative semiochemicals bound to CcOBP2, a protein specifically expressed in antennae, 14 compounds from the pupae of H. cunea and 11 common volatile compounds from plants were selected for competitive fluorescence binding assay. The result of the binding assay showed that five compounds were able to bind toCcOBP2. The electroantennogram (EAG) demonstrated that the antennae had a significant response to the 3-Carene, a bicyclic monoterpene, and C. cunea could be obviously attracted by this compound. The behavioral response to 3- carene was dramatically weakened when CcOBP2 was specifically knocked down. The molecular docking result indicated that several amino acids especially Ile-81, Val-122, Phe-123 of CcOBP2 were responsible for binding to 3-Carene. Furthermore, there was a repellent effect on the host H. cunea with the treatment of the 3-Carene. This study illustrated that CcOBP2 might be a crucial protein involved in the olfactory signaling pathway and the 3-Carene, secreted from plants, could probably have a potential role in repelling pests as well as attracting natural enemies.