Identification and expression profile analysis of putative odorant-binding proteins in Sitodiplosis mosellana (Gehin) (Diptera: Cecidomyiidae)

Identification and expression profile analysis of chemosensory genes in pine needle gall midge, Thecodiplosis japonensis (Diptera: Cecidomyiidae)

Insects have highly specialized and sensitive olfactory systems involving several chemosensory genes to locate their mates and hosts or escape from predators. Pine needle gall midge, Thecodiplosis japonensis (Diptera: Cecidomyiidae), has invaded China since 2016 and caused serious damage. Till now, there is no environmentally friendly measure to control this gall midge. Screening molecules with high affinity to target odorant-binding protein to develop highly efficient attractants is a potential pest management method. However, the chemosensory genes in T. japonensis are still unclear. We identified 67 chemosensory-related genes in the transcriptomes of antennae, including 26 OBPs, 2 CSPs, 17 ORs, 3 SNMPs, 6 GRs, and 13 IRs, using high throughput sequencing. Phylogenetic analysis of these six chemosensory gene families among Dipteran was performed to classify and predict the functions. The expression profiles of OBPs, CSPs and ORs were validated by quantitative real-time PCR. 16 of the 26 OBPs were biased expressed in antennae. TjapORco and TjapOR5 were highly expressed in the antenna of unmated male and female adults. The functions of related OBPs and ORs genes were also discussed. These results provide a basis for the functional research on chemosensory genes at the molecular level.

Modular synthesis of the pheromone (2S,7S)-2,7-nonanediyl dibutyrate and its racemate and their field efficacy to control orange wheat blossom midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae)

BACKGROUND

Sudden outbreaks of the orange wheat blossom midge, Sitodiplosis mosellana (Géhin) cause huge wheat yield losses. Use of sex pheromones is more efficient than laborious egg counting to monitor these hidden-concealed insects. Quick synthesis of the sex pheromones is therefore required to meet the sudden outbreak needs.

RESULTS

A synthetic approach of stereospecific and racemic S. mosellana pheromones was presented. This method afforded the stereospecific and racemic S. mosellana pheromones in three steps and high enantioselectivity (> 98% ee for (2S,7S)-2,7-nonanediyl dibutyrate) in less than 1 day with 74% and 73% overall yields, respectively, whereas most conventional methods require longer synthesis time with less than 40% yield. The synthesis routes could quickly and economically afford the pheromones, starting from synthon (S)-but-3-yn-2-ol (1a) or but-3-yn-2-ol (1b), through the same three-step processes of coupling, reduction, and esterification. The Y-tube olfactometer results showed significant attractiveness of the synthetic stereospecific and racemic sex pheromones to S. mosellana males relative to the blank control (P < 0.001). Field trials also demonstrated significant attractiveness of the synthetic stereospecific and racemic sex pheromones relative to the blank control (P < 0.001).

CONCLUSION

This modular approach is conducive to the deployment of field traps and timely responses to S. mosellana outbreaks and can be a time-saving and cost-effective tool to manage S. mosellana. © 2022 Society of Chemical Industry.

Functional Characterization of Odorant Binding Protein PyasOBP2 From the Jujube Bud Weevil, Pachyrhinus yasumatsui (Coleoptera: Curculionidae)

Odorant binding proteins (OBPs) play an important role in insect olfaction. The jujube bud weevil Pachyrhinus yasumatsui (Coleoptera: Curculionidae) is a major pest of Zizyphus jujuba in northern China. In the present study, based on the antennal transcriptome, an OBP gene of P. yasumatsui (PyasOBP2) was cloned by reverse transcription PCR (RT-PCR). Expression profile analyses by quantitative real-time PCR (qRT-PCR) revealed that PyasOBP2 was highly expressed in the antennae of both male and female P. yasumatsui adults, while its expression was negligible in other tissues. PyasOBP2 was prokaryotically expressed, and purified by Ni-NTA resin. The fluorescence competitive binding assays with 38 plant volatiles from Z. jujuba showed that PyasOBP2 could bind with a broad range of plant volatiles, and had strongest binding capacities to host-plant volatiles like ethyl butyrate (K_i = 3.02 μM), 2-methyl-1-phenylpropene (K_i = 4.61 μM) and dipentene (K_i = 5.99 μM). The three dimensional structure of PyasOBP2 was predicted by homology modeling, and the crystal structure of AgamOBP1 (PDB ID: 2erb) was used as a template. The molecular docking results indicated that the amino acid residue Phe114 of PyasOBP2 could form hydrogen bonds or hydrophobic interactions with some specific ligands, so this residue might play a key role in perception of host plant volatiles. Our results provide a basis for further investigation of potential functions of PyasOBP2, and development of efficient monitoring and integrated pest management strategies of P. yasumatsui.

Binding Affinity Characterization of Four Antennae-Enriched Odorant-Binding Proteins From Harmonia axyridis (Coleoptera: Coccinellidae)

Harmonia axyridis is an important natural enemy that consumes many agricultural and forestry pests. It relies on a sensitive olfactory system to find prey and mates. Odorant-binding proteins (OBPs) as the first-step of recognizing volatiles, transport odors through sensillum lymph to odorant receptors (ORs). However, little is known about the molecular mechanisms of H. axyridis olfaction. In this study, four H. axyridis antenna specific OBP genes, HaxyOBP3, 5, 12, and 15, were bacterially expressed and the binding features of the four recombinant proteins to 40 substances were investigated using fluorescence competitive binding assays. Three-dimensional structure modeling and molecular docking analysis predicted the binding sites between HaxyOBPs and candidate volatiles. Developmental expression analyses showed that the four HaxyOBP genes displayed a variety of expression patterns at different development stages. The expression levels of HaxyOBP3 and HaxyOBP15 were higher in the adult stage than in the other developmental stages, and HaxyOBP15 was significantly transcriptionally enriched in adult stage. Ligand-binding analysis demonstrated that HaxyOBP3 and HaxyOBP12 only combined with two compounds, β-ionone and p-anisaldehyde. HaxyOBP5 protein displayed binding affinities with methyl salicylate, β-ionone, and p-anisaldehyde (Ki = 18.15, 11.71, and 13.45 μM). HaxyOBP15 protein had a broad binding profile with (E)-β-farnesene, β-ionone, α-ionone, geranyl acetate, nonyl aldehyde, dihydro-β-ionone, and linalyl acetate (Ki = 4.33-31.01 μM), and hydrophobic interactions played a key role in the binding of HaxyOBP15 to these substances according to molecular docking. Taken together, HaxyOBP15 exhibited a broader ligand-binding spectrum and a higher expression in adult stage than HaxyOBP3, 5, and 12, indicating HaxyOBP15 may play a greater role in binding volatiles than other three HaxyOBPs. The results will increase our understanding of the molecular mechanism of H. axyridis olfaction and may also result in new management strategies (attractants/repellents) that increase the biological control efficacy of H. axyridis.

Genes involved in the Type I pheromone biosynthesis pathway and chemoreception from the sex pheromone gland transcriptome of Dioryctria abietella

Dioryctria abietella is a coniferous seed orchard pest that can damage a series of host plants and cause huge losses to the forest economy. Sex pheromones play an important role in lepidopteran sex communication for reproduction and can be used as biological control agents to monitor and trap pests. However, the genes involved in the biosynthesis, transportation, and degradation of D. abietella sex pheromones have not been studied extensively. Transcriptome analysis of female D. abietella sex pheromone glands (PGs) revealed that 210 candidate genes might be involved in sex pheromone biosynthesis (139 genes) and chemoreception systems (71 genes). The gene expression patterns exhibited four desaturase genes (DabiDES4-7) and one fatty acid reductase gene (DabiFAR6), which were more highly expressed in sex pheromone glands than in other tissues, suggesting that these enzymes play an important role in D. abietella sex pheromone synthesis. In addition, most DabiOBPs showed high expression in antennae, but only DabiOBP4 exhibited specific expression in sex pheromone glands, suggesting that they may play many physiological roles in D. abietella. We put forth a reasonable hypothesis about type I pheromone biosynthesis pathways based on these genes identified in the D. abietella sex pheromone gland transcriptome. Our findings lay a foundation for population monitoring, mating disruption, mass trapping, and the development of ecologically acceptable management strategies.

Identification and analysis of olfactory genes in Dioryctria abietella based on the antennal transcriptome

The coneworm Dioryctria abietella (Lepidoptera: Pyralidae) is an economy devastating pest that infests many valuable conifer species in the Holarctic regions, such as Pinus koraiensis Siebold and Zucc. The chemosensory system plays a crucial role in the mating, foraging, and ovipositing of this pest, and therefore it is desirable to identify chemosensory molecules for pest control. However, little is known at molecular level about the olfactory mechanisms in D. abietella. In the present study, we first established antennal transcriptomes of D. abietella and identified 132 putative chemosensory genes, including 15 odorant-binding proteins, 18 chemosensory proteins, 65 odorant receptors, 5 sensory neuron membrane proteins, 24 ionotropic receptors, and 5 gustatory receptors. In addition, phylogenetic trees were constructed for chemosensory genes to investigate the orthologs between D. abietella and other species of insects. Furthermore, we also compared the patterns of motifs between OBPs and CSPs using MEME. Additionally, we observed that most of DabiOBPs and DabiCSPs had the antenna-biased expression by quantitative real-time PCR (RT-qPCR), and there was a higher expression of DabiPBP1 and DabiPBP2 in male antennae than in female antennae. The binding sites of DabiPBPs (DabiPBP1, DabiPBP2) and DabiPRs (DabiOR19, DabiOR31) to the sex pheromone were predicted well by three-dimensional docking structure modelling and molecular docking. Our finding supplied a foundation for further research on the binding process of OBPs or CSPs and sensing process of ORs, SNMPs, IRs or GRs in D. abietella.

Functional Analysis of Odorant-Binding Proteins 12 and 17 from Wheat Blossom Midge Sitodiplosis mosellana Géhin (Diptera: Cecidomyiidae)

Simple Summary

Sitodiplosis mosellana is one of the most destructive pests of wheat. Adults rely highly on wheat spike volatiles to search and locate oviposition sites. Insect odorant-binding proteins (OBPs) are important in binding and transporting host plant volatiles to the olfactory receptors. Therefore, OBP-based behavioral interference is believed to be a novel and effective pest management strategy. The objectives of this study were to clone two S. mosellana female antenna-enriched OBP genes (SmosOBP12 and SmosOBP17), determine the functions of the encoded SmosOBP proteins in binding wheat volatiles, and investigate behavioral responses of female S. mosellana to odorant molecules. Results indicated that SmosOBP12 had a broader ligand-binding spectrum than SmosOBP17 to wheat volatiles. Female S. mosellana showed intensive response to 3-hexanol, 1-octen-3-ol, D-panthenol, 3-carene, (Z)-3-hexenylacetate, hexyl acetate, methyl salicylate, heptyl acetate, ethyl heptanoate, α-farnesene, and ocimene. Notably, all these compounds except α-farnesene exhibited strong affinity to SmosOBP12. In conclusion, SmosOBP12 may play more crucial roles than SmosOBP17 in perception and transportation of biologically active host volatiles. This information has enhanced our molecular understanding of the S. mosellana olfaction, which could also serve as an important reference for developing attractants or repellents to control this pest.

Abstract

The wheat blossom midge Sitodiplosis mosellana, one of the most disastrous wheat pests, depends highly on olfactory cues to track suitable plants. To better understand the olfactory recognition mechanisms involved in host selection, in the present study we cloned two S. mosellana adult antenna-specific odorant binding protein (OBP) genes, SmosOBP12 and SmosOBP17, and evaluated bacterially expressed recombinant proteins for their selectivity and sensitivity for host wheat volatiles using the fluorescence-based ligand binding assay. The results showed that both SmosOBPs effectively bound alcohol, ester, ketone, and terpenoid compounds. Particularly, SmosOBP12 had significantly higher affinities (K_i < 10.5 μM) than SmosOBP17 (K_i2 > 0.1 μM) to 3-hexanol, 1-octen-3-ol, D-panthenol, 3-carene, (Z)-3-hexenylacetate, hexyl acetate, methyl salicylate, heptyl acetate, and ethyl heptanoate. Consistently, S. mosellana females were attracted to all these chemicals in a behavioral assay using Y-tube olfactometer. SmosOBP12 also bound aldehyde, but neither bound alkanes. Notably, SmosOBP12 exhibited strong affinity to ocimene (K_i = 8.2 μM) that repelled S. mosellana. SmosOBP17, however, was insensitive to this compound. Taken together, our results indicate that SmosOBP12 may play a greater role than SmosOBP17 in perceiving these biologically active plant volatiles.

Identification and Expression Profile Analysis of Chemosensory Genes From the Antennal Transcriptome of Bamboo Locust (Ceracris kiangsu)

Studies of chemosensory genes are key to a better understanding of intra- and interspecific communications between insects and their environment and provide opportunities for developing environmentally friendly pesticides to target pest species. The bamboo locust Ceracris kiangsu Tsai (Orthoptera: Acrididae) is one of the most important bamboo leaf-eating insects in southern China. However, the genes underlying olfactory sensation are lacking in the bamboo locust. In this study, the transcriptomes of male and female C. kiangsu antennae were sequenced and analyzed. A total of 125 chemosensory genes, including 91 odorant receptors (ORs), 13 ionotropic receptors (IRs), 13 odorant-binding proteins (OBPs), six chemosensory proteins (CSPs), and two sensory neuron membrane proteins, were identified based on sequence alignment and phylogenetic analyses. The expression patterns of all candidate genes on the antennae of males and females, maxillary palps, tarsi, wings, and thoraxes-abdomens were confirmed by real-time quantitative PCR. The analyses demonstrated that most genes are highly expressed in the antennae, and 35 ORs, 7 IRs, 10 OBPs, and 1 CSP exhibit significantly male-biased expression patterns, indicating their potential functions in mating behavior and the recognition of female sex pheromones. In addition to the antennal-predominant genes, some were abundant in the maxillary palps and some in the non-olfactory tissues, suggesting their different functions in the olfactory system of C. kiangsu. Our research offers an extensive resource for investigating the chemoreception mechanism of C. kiangsu. Further studies of olfactory function will provide comprehensive methods and original strategies for integrated pest management.

Molecular and functional characterization of three odorant-binding proteins from the wheat blossom midge, Sitodiplosis mosellana

Sitodiplosis mosellana, a periodic but devastating wheat pest, relies on wheat spike volatiles as a cue in selecting hosts for oviposition. Insect odorant-binding proteins (OBPs) are thought to play essential roles in filtering, binding and transporting hydrophobic odorant molecules to specific receptors. To date, the molecular mechanisms underlying S. mosellana olfaction are poorly understood. Here, three S. mosellana antenna-specific OBP genes, SmosOBP11, 16 and 21, were cloned and bacterially expressed. Binding properties of the recombinant proteins to 28 volatiles emitted from wheat spikes were investigated using fluorescence competitive binding assays. Sequence analysis suggested that these SmosOBPs belong to the Classic OBP subfamily. Ligand-binding analysis showed that all three SmosOBPs preferentially bound alcohol, ester and ketone compounds, and SmosOBP11 and 16 also selectively bound terpenoid compounds. In particular, the three SmosOBPs had high binding affinities (K_i < 20 μmol/L) to 3-hexanol and cis-3-hexenylacetate that elicited strong electroantennogram (EAG) response from female antennae. In addition, SmosOBP11 displayed significantly higher binding (K_i < 8 μmol/L) than SmosOBP16 and 21 to 1-octen-3-ol, D-panthenol, α-pinene and heptyl acetate which elicited significant EAG response, suggesting that SmosOBP11 plays a major role in recognition and transportation of these volatiles. These findings have provided important insight into the molecular mechanism by which S. mosellana specifically recognizes plant volatiles for host selection, and have facilitated identification of effective volatile attractants that are potentially useful for pest monitoring and trapping.

Sex- and Tissue-Specific Expression Profiles of Odorant Binding Protein and Chemosensory Protein Genes in Bradysia odoriphaga (Diptera: Sciaridae)

Bradysia odoriphaga is an agricultural pest insect affecting the production of Chinese chive and other liliaceous vegetables in China, and it is significantly attracted by sex pheromones and the volatiles derived from host plants. Despite verification of this chemosensory behavior, however, it is still unknown how B. odoriphaga recognizes these volatile compounds on the molecular level. Many of odorant binding proteins (OBPs) and chemosensory proteins (CSPs) play crucial roles in olfactory perception. Here, we identified 49 OBP and 5 CSP genes from the antennae and body transcriptomes of female and male adults of B. odoriphaga, respectively. Sequence alignment and phylogenetic analysis among Dipteran OBPs and CSPs were analyzed. The sex- and tissue-specific expression profiles of 54 putative chemosensory genes among different tissues were investigated by quantitative real-time PCR (qRT-PCR). qRT-PCR analysis results suggested that 22 OBP and 3 CSP genes were enriched in the antennae, indicating they might be essential for detection of general odorants and pheromones. Among these antennae-enriched genes, nine OBPs (BodoOBP2/4/6/8/12/13/20/28/33) were enriched in the male antennae and may play crucial roles in the detection of sex pheromones. Moreover, some OBP and CSP genes were enriched in non-antennae tissues, such as in the legs (BodoOBP3/9/19/21/34/35/38/39/45 and BodoCSP1), wings (BodoOBP17/30/32/37/44), abdomens and thoraxes (BodoOBP29/36), and heads (BodoOBP14/23/31 and BodoCSP2), suggesting that these genes might be involved in olfactory, gustatory, or other physiological processes. Our findings provide a starting point to facilitate functional research of these chemosensory genes in B. odoriphaga at the molecular level.

Identification of odorant-binding protein genes in Galeruca daurica (Coleoptera: Chrysomelidae) and analysis of their expression profiles

Odorant-binding proteins (OBPs) play a fundamental role in insect olfaction. In recent years, Galeruca daurica (Joannis) (Coleoptera: Chrysomelidae) has become one of the most important insect pests in the Inner Mongolian grasslands of China. This pest only feeds on the species of Allium plants, implying the central role of olfaction in its search for specific host plants. However, the olfaction-related proteins have not been investigated in this beetle. In this study, we identified 29 putative OBP genes, namely GdauOBP1-29, from the transcriptome database of G. daurica assembled in our laboratory by using RNA-Seq. All 29 genes had the full-length open reading frames except GdauOBP29, encoding proteins in length from 119 to 202 amino acids with their predicted molecular weights from 12 to 22 kDa with isoelectric points from 3.88 to 8.84. Predicted signal peptides consisting of 15-22 amino acid residues were found in all except GdauOBP6, GdauOBP13 and GdauOBP29. The amino acid sequence identity between the 29 OBPs ranged 8.33-71.83%. GdauOBP1-12 belongs to the Classic OBPs, while the others belong with the Minus-C OBPs. Phylogenetic analysis indicated that GdauOBPs are the closest to CbowOBPs from Colaphellus bowringi. RT-PCR and qRT-PCR analyses showed that all GdauOBPs were expressed in adult antennae, 11 of which with significant differences in their expression levels between males and females. Most GdauOBPs were also expressed in adult heads (without antennae), thoraxes, abdomens, legs and wings. Moreover, the expression levels of the GdauOBPs varied during the different development stages of G. daurica with most GdauOBPs expressed highly in the adult antennae but scarcely in eggs and pupae. These results provide insights for further research on the molecular mechanisms of chemical communications in G. daurica.

Identification of putative odorant binding protein genes in Asecodes hispinarum, a parasitoid of coconut leaf beetle (Brontispa longissima) by antennal RNA-Seq analysis

Asecodes hispinarum (Hymenoptera: Eulophidae) is an endoparasitoid and an efficient biological control agent which attacks larvae of Brontispa longissima, a serious insect pest of Palmae plants in China. Odorant binding proteins (OBPs) are believed to be important for transporting semiochemicals through the aqueous sensillar lymph to the olfactory receptor cells within the insect antennal sensilla. No previous study has reported on OBPs in A. hispinarum. In this study, we conducted the large-scale identification of OBP genes from the antennae of A. hispinarum by using transcriptome sequencing. Approximately 28.4 million total raw reads and about 27.3 million total clean reads were obtained, and then 46,363 unigenes were assembled. Of these unigenes, a total of 21,263 can be annotated in the NCBI non-redundant database. Among the annotated unigenes, 16,623 of them can be assigned to GO (Gene Ontology). Furthermore, we identified 8 putative OBP genes, and a phylogenetic tree analysis was performed to characterize the 8 OBP genes. In addition, the expression of the 8 OBP genes in different A. hispinarum body tissues was analyzed by real-time quantitative polymerase chain reaction (qRT-PCR). The results indicated that the 8 OBP genes were expressed accordingly to sexes and tissues, but all highly expressed in antennae. The finding of this study will lay the foundation for unraveling molecular mechanisms of A. hispinarum chemoperception.