Evolution and functional analysis of odorant-binding proteins in three rice planthoppers: Nilaparvata lugens, Sogatella furcifera, and Laodelphax striatellus

Nanoparticle-delivered RNAi-based pesticide target screening for the rice pest white-backed planthopper and risk assessment for a natural predator

Vacuolar-type (H+)-ATPase (vATPase) is a conserved multi-subunit eukaryotic enzyme composed of 14 subunits that form a functional complex consisting of an ATP-hydrolytic domain (V1) and a proton-translocation domain (V0). ATP hydrolysis and subsequent H+ translocation rely heavily on a fully assembled V1/V0 complex. Since vATPase is crucial for insect survival, it is a viable molecular target for pest control. However, detailed functional analyses of the 14 subunits and their suitability for pest control have not been fully explored in a single insect species. In this study, we identified 22 vATPase subunit transcripts that correspond to 13 subunits (A1, A2, B, C, D, E, F, G, H, a1, a2, c and d) in the white-backed planthopper (WBPH), Sogatella furcifera, a major hemipteran pest of rice. RNAi screens using microinjection and spray-based methods revealed that the SfVHA-F, SfVHA-a2 and SfVHA-c2 subunits are critical. Furthermore, star polymer (SPc) nanoparticles were utilized to conduct spray-induced and nanoparticle-delivered gene silencing (SI-NDGS) to evaluate the pest control efficacy of RNAi targeting the SfVHA-F, SfVHA-a2 and SfVHA-c2 transcripts. Target mRNA levels and vATPase enzymatic activity were both reduced. Honeydew excreta was likewise reduced in WBPH treated with dsRNAs targeting SfVHA-F, SfVHA-a2 and SfVHA-c2. To assess the environmental safety of the nanoparticle-wrapped dsRNAs, Cyrtorhinus lividipennis Reuter, a major natural enemy of planthoppers, was also sprayed with dsRNAs targeting SfVHA-F, SfVHA-a2 and SfVHA-c2. Post-spray effects of dsSfVHA-a2 and dsSfVHA-c2 on C. lividipennis were innocuous. This study identifies SfVHA-a2 and SfVHA-c2 as promising targets for biorational control of WBPH and lays the foundation for developing environment-friendly RNAi biopesticides.

Binding properties of chemosensory protein 4 in Riptortus pedestris to aggregation pheromones

In insects, chemosensory proteins (CSPs) play an important role in the perception of the external environment and have been widely used for protein-binding characterization. Riptortus pedestris has received increased attention as a potential cause of soybean staygreen syndrome in recent years. In this study, we found that RpedCSP4 expression in the antennae of adult R. pedestris increased with age, with no significant difference in expression level observed between males and females, as determined through quantitative real-time polymerase chain reaction (qRT-PCR). Subsequently, we investigated the ability of RpedCSP4 to bind various ligands (five aggregated pheromone components and 13 soybean volatiles) using a prokaryotic expression system and fluorescence competitive binding assays. We found that RpedCSP4 binds to three aggregated pheromone components of R. pedestris, namely, ((E)-2-hexenyl (Z)-3-hexenoate (E2Z3), (E)-2-hexenyl (E)-2-hexenoate (E2E2), and (E)-2-hexenyl hexenoate (E2HH)), and that its binding capacities are most stable under acidic condition. Finally, the structure and protein-ligand interactions of RpedCSP4 were further analyzed via homology modeling, molecular docking, and targeted mutagenesis experiments. The L29A mutant exhibited a loss of binding ability to these three aggregated pheromone components. Our results show that the olfactory function of RpedCSP4 provides new insights into the binding mechanism of RpedCSPs to aggregation pheromones and contributes to discover new target candidates that will provide a theoretical basis for future population control of R. pedestris.

Identification of odorant-binding proteins and functional analysis of antenna-specific BhorOBP28 in Batocera horsfieldi (Hope)

BACKGROUND

The important wood-boring pest Batocera horsfieldi has evolved a sensitive olfactory system to locate host plants. Odorant-binding proteins (OBPs) are thought to play key roles in olfactory recognition. Therefore, exploring the physiological function of OBPs could facilitate a better understanding of insect chemical communications.

RESULTS

In this research, 36 BhorOBPs genes were identified via transcriptome sequencing of adults' antennae from B. horsfieldi, and most BhorOBPs were predominantly expressed in chemosensory body parts. Through fluorescence competitive binding and fluorescence quenching assays, the antenna-specific BhorOBP28 was investigated and displayed strong binding affinities forming stable complexes with five volatiles, including (+)-α-Pinene, (+)-Limonene, β-Pinene, (-)-Limonene, and (+)-Longifolene, which could also elicit conformation changes when they were interacting with BhorOBP28. Batocera horsfieldi females exhibited a preference for (-)-Limonene, and a repellent response to (+)-Longifolene. Feeding dsOBP19 produced by a bacteria-expressed system with a newly constructed vector could lead to the knockdown of BhorOBP28, and could further impair B. horsfieldi attraction to (-)-Limonene and repellent activity of (+)-Longifolene. The analysis of site-directed mutagenesis revealed that Leu7, Leu72, and Phe121 play a vital role in selectively binding properties of BhorOBP28.

CONCLUSION

By modeling the molecular mechanism of olfactory recognition, these results demonstrate that BhorOBP28 is involved in the chemoreception of B. horsfieldi. The bacterial-expressed dsRNA delivery system gains new insights into potential population management strategies. Through the olfactory process concluded that discovering novel behavioral regulation and environmentally friendly control options for B. horsfieldi in the future. © 2024 Society of Chemical Industry.

Binding Properties of Odorant Binding Protein 37 in Plagiodera versicolora to Host Volatile, o-Cymene

The chemosensory system plays an important role in the host plants location. Plagiodera versicolora (Coleoptera: Chrysomelidae) is a worldwide leaf-eating forest pest that feeds exclusively on salicaceous trees. There is no function study of odorant binding proteins (OBPs) in P. versicolora. In the current study, we found that PverOBP37 has a high expression in male and female antennae, heads, and legs by quantitative real-time PCR. The binding properties of PverOBP37 to 18 host plant volatiles were determined by fluorescence competition binding assays. The results showed that PverOBP37 could bind to the host plant volatile, o-cymene. Furthermore, four candidate key amino acid residues (F8, Y50, F103, and R107) of PverOBP37 to o-cymene were identified by molecular docking. The functional assay to confirm Y50, F103, and R107 mutations were key amino acid residues of PverOBP37 involved in the binding to o-cymene. Knockdown of PverOBP37 and Y-tube behavioral bioassays of mated females led to a significantly reduced attraction to o-cymene. This study not only revealed the molecular mechanism of PverOBP37 but also suggested that PverOBP37 is essential to detect host plant volatiles as cues to search for egg-laying sites in P. versicolora.

Different binding properties of odorant-binding protein 8 to insecticides in Orius sauteri

Chemical sensing systems are vital in the growth and development of insects. Orius sauteri (Poppius) (Hemiptera: Anthocoridae) is an important natural enemy of many pests. The molecular mechanism of odorant binding proteins (OBPs) binding with common insecticides is still unknow in O. sauteri. In this study, we expressed in vitro OsauOBP8 and conducted fluorescence competition binding assay to investigate the function of OsauOBP8 to insecticides. The results showed that OsauOBP8 could bind with four common insecticides (phoxim, fenitrothion, chlorpyrifos, deltamethrin). Subsequently, we used molecular docking to predict and obtained candidate six amino acid residues (K4, K6, K13, R31, K49, K55) and then mutated. The result showed that three key residues (K4, K6, R31) play important role in OsauOBP8 bound to insecticides. Our study identified the key binding sites of OsauOBP8 to insecticides and help to better understand the molecular mechanism of OBPs to insecticides in O. sauteri.

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.

Efficient nanoparticle-based CRISPR-Cas13d induced mRNA disruption of an eye pigmentation gene in the white-backed planthopper, Sogatella furcifera

The discovery of the clustered regularly interspaced short palindromic repeat (CRISPR) system has driven gene manipulation technology to a new era with applications reported in organisms that span the tree of life. The utility of CRISPR-mediated editing was further expanded to mRNA following identification of the RNA-targeting Cas13 family of smaller endonuclease proteins. Application of this family to insect research, however, has been more limited. In this study, the smallest Cas13 family member, Cas13d, and guide RNAs (gRNAs) were complexed with a versatile nanomaterial (star polycation, SPc) to generate a proof-of-concept RNA-editing platform capable of disrupting mRNA expression of the eye pigmentation gene tryptophan 2,3-dioxygenase (SfTO) in white-backed planthoppers (WBPHs). The resulting red-eye phenotype was present in 19.76% (with SPc) and 22.99% (without SPc) of the treatment groups and was comparable to the red-eye phenotype generated following conventional RNA interference knockdown (22.22%). Furthermore, the Cas13/gRNA phenotype manifested more quickly than RNA interference. Consistent with the expected Cas13d mechanism, SfTO transcript levels were significantly reduced. Taken together, the results indicate that the SPc-CRISPR-Cas13d/gRNA complex negatively impacted expression of the target gene. These findings confirm the utility of this novel mRNA disruption system in insects and lay the foundation for further development of these tools in the implementation of green agricultural pest management tactics.

A systematic review of southern rice black-streaked dwarf virus in the age of omics

Southern rice black-streaked dwarf virus (SRBSDV) is one of the most damaging rice viruses. The virus decreases rice quality and yield, and poses a serious threat to food security. From this perspective, this review performed a survey of published studies in recent years to understand the current status of SRBSDV and white-backed planthopper (WBPH, Sogatella furcifera) transmission processes in rice. Recent studies have shown that the interactions between viral virulence proteins and rice susceptibility factors shape the transmission of SRBSDV. Moreover, the transmission of SRBSDV is influenced by the interactions between viral virulence proteins and S. furcifera susceptibility factors. This review focused on the molecular mechanisms of key genes or proteins associated with SRBSDV infection in rice via the S. furcifera vector, and the host defense response mechanisms against viral infection. A sustainable control strategy using RNAi was summarized to address this pest. Finally, we also present a model for screening anti-SRBSDV inhibitors using viral proteins as targets. © 2023 Society of Chemical Industry.

Binding properties of chemosensory protein 12 in Riptortus pedestris to aggregation pheromone (E)-2-hexenyl (Z)-3-hexenoate

Riptortus pedestris (bean bug), a common soybean pest, has a highly developed olfactory system to find hosts for feeding and oviposition. Chemosensory proteins (CSPs) have been identified in many insect species; however, their functions in R. pedestris remain unknown. In this study, quantitative real time-polymerase chain reaction (qRT-PCR) revealed that the expression of RpedCSP12 in the adult antennae of R. pedestris increased with age. Moreover, a significant difference in the expression levels of RpedCSP12 was observed between male and female antennae at one and three days of age. We also investigated the binding ability of RpedCSP12 to different ligands using a prokaryotic expression system and fluorescence competitive binding assays. We found that RpedCSP12 only bound to one aggregation pheromone, (E)-2-hexenyl (Z)-3-hexenoate, and its binding decreased with increasing pH. Furthermore, homology modelling, molecular docking, and site-directed mutagenesis revealed that the Y27A, L74A, and L85A mutants lost their binding ability to (E)-2-hexenyl (Z)-3-hexenoate. Our findings highlight the olfactory roles of RpedCSP12, providing insights into the mechanism by which RpedCSPs bind to aggregation pheromones. Therefore, our study can be used as a theoretical basis for the population control of R. pedestris in the future.

Behavioral, Electrophysiological, and Toxicological Responses of Plutella xylostella to Extracts from Angelica pubescens

Plutella xylostella L. is a destructive pest affecting cruciferous vegetables, causing massive economic losses worldwide. Plant-based insecticides are considered promising insect control agents. The Angelica pubescens extract inhibited female oviposition, with an oviposition deterrence index (ODI) of 61.65% at 12.5 mg/mL. We aimed to identify the bioactive compounds in A. pubescens extract. The compounds from A. pubescens extract were analyzed using LC-MS techniques. The toxicity and behavioral responses of larvae and adults of P. xylostella to ten compounds were investigated. We found that the caryophyllene oxide and 3,4-dimethoxycinnamic acid inhibited female oviposition; the ODIs were 98.31% and 97.59% at 1.25 mg/mL, respectively. The A. pubescens extract, caryophyllene oxide, and 3,4-dimethoxycinnamic acid caused larval mortality, with LC₅₀ values of 21.31, 4.56, and 5.52 mg/mL, respectively. The EAG response of females was higher than that of males under A. pubescens extract conditions, while the EAG response of males was higher than that of females in caryophyllene oxide and 3,4-dimethoxycinnamic acid conditions. The A. pubescens extract and caryophyllene oxide showed repellent activity against both female and male adults, while the 3,4-dimethoxycinnamic acid did not elicit any notable behavioral responses from P. xylostella adults. A. pubescens extract and caryophyllene oxide are potential insecticides, oviposition deterrents, and behavioral regulators against P. xylostella, and they could be potential candidates for the development of biological insecticides to control P. xylostella.

Ligand-binding properties of chemosensory protein 1 in Callosobruchus chinensis to mung bean volatiles

Callosobruchus chinensis (Coleoptera: Fabaceae) is a worldwide pest that feeds exclusively on legumes, and is the most serious pest affecting mung beans. Usually, the insect olfactory system plays a predominant role in searching for host plants and egg-laying locations. Chemosensory proteins (CSPs), are mainly responsible for transporting specific odour molecules from the environment. In this study, we found that the CSP1 gene of adult C. chinensis displayed antennae-biased expression using quantitative real-time PCR (qRT-PCR) analysis. The binding properties of 23 mung bean volatiles were then determined through several analyses of in vitro recombinant CSP1 protein, including fluorescence competitive binding assay, homology modelling, molecular docking, and site-directed mutagenesis. Fluorescence competitive binding assays showed that CchiCSP1 protein could bind to four mung bean volatiles and was most stable at pH 7.4. After site-directed mutation of three key amino acid bases (L39, V25, and Y35), their binding affinities to each ligand were significantly decreased or lost. This indicated that these three amino acid residues may be involved in the binding of CchiCSP1 to different ligands. We further used Y-tube behavioural bioassays to find that the four mung bean volatiles had a significant attraction or repulsion response in adult C. chinensis. The above findings confirm that the CchiCSP1 protein may be involved in the response of C. chinensis to mung bean volatiles and plays an important role in olfactory-related behaviours. The four active volatiles are expected to develop into new behavioural attractants or repellents in the future.

A plant virus enhances odorant-binding protein 5 (OBP5) in the vector whitefly for more actively olfactory orientation to the host plant

BACKGROUND

The whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is a notorious agricultural pest and the effective vector of many plant viruses worldwide. Cucurbit chlorotic yellows virus (CCYV), exclusively transmitted by B. tabaci in a semipersistent manner, is a serious causal agent in cucurbit crops in many countries. Plant viruses can manipulate the behaviors of insect vectors to promote the spread of themselves, but underlying mechanisms are remaining unclear.

RESULTS

In this study, our observations indicated that B. tabaci, when carrying CCYV, oriented more actively to the host plant cucumber. Transcriptome analysis and quantitative polymerase chain reaction with reverse transcription analysis showed that the odorant-binding protein 5 (OBP5) was upregulated with viral acquisition. Sequence and phylogenetic analysis showed that BtabOBP5 was highly homologous with nine OBPs from other hemipteran insects. In addition, OBP5-silenced whiteflies significantly altered their orientation behavior towards cucumber plants and towards some typical volatile organic compounds released from cucumbers.

CONCLUSION

This study described a novel mechanism by which the olfactory system of vector insects could be regulated by a semipersistent plant virus, thereby affecting insect olfactory behavior and relationship with host plants. These results provided a basis for developing potential olfaction-based pest management strategies in the future. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Odorant-Binding Protein 6 Contributes High Binding Affinity to Insecticides in a Parasitic Wasp Meteorus pulchricornis (Hymenoptera: Braconidae)

Meteorus pulchricornis is a preponderant parasitic wasp of various lepidopteran pests. The extensive application of broad-spectrum insecticides usually causes serious threats to the olfactory recognition of nontarget insects such as parasitoid wasps. However, the binding mechanism of odorant-binding proteins (OBPs) to insecticides in parasitoid wasps remains unknown. Herein, we find that the MpulOBP6 protein had a strong binding affinity to three insecticides (phoxim, chlorpyrifos, and chlorfenapyr). Results of computational simulations revealed that the hydrophobic interaction contributed by a mass of nonpolar amino acid residues was the primary driving force in the formation and stabilization of MpulOBP6-insecticide complexes. Among them, four residues (Met75, Val84, Phe121, and Pro122) and two residues (Val84 and Phe111) play an essential role in the binding of MpulOBP6 to phoxim and chlorfenapyr, respectively. Our findings could be instrumental to elucidate the effects of insecticide application toward the olfactory recognition of nontarget insects in the processes of agricultural production.

Functional characterization of five developmental signaling network genes in the white-backed planthopper: Potential application for pest management

BACKGROUND

The white-backed planthopper (WBPH, Sogatella furcifera) is a major rice pest that exhibits condition dependent wing dimorphisms - a macropterous (long wing) form and a brachypterous (short wing) form. Although, the gene cascade that regulates wing development and dimorphic differentiation has been largely defined, the utility of these genes as targets for pest control has yet to be fully explored.

RESULTS

Five genes typically associated with the developmental signaling network, armadillo (arm), apterous A (apA), scalloped (sd), dachs (d), and yorkie (yki) were identified from the WBPH genome and their roles in wing development assessed following RNA interference (RNAi)-mediated knockdown. At 5 days-post injection, transcript levels for all five targets were substantially decreased compared with the dsGFP control group. Among the treatment groups, those injected with dsSfarm had the most pronounced effects on transcript reduction, mortality (95 ± 3%), and incidence (45 ± 3%) of wing deformities, whereas those injected with dsSfyki had the lowest incidence (6.7 ± 4%). To assess the utility of topical RNAi for Sfarm, we used a spray-based approach that complexed a large-scale, bacteria-based double-stranded RNA (dsRNA) expression pipeline with star polycation (SPc) nanoparticles. Rice seedlings infested with third and fourth instar nymphs were sprayed with SPc-dsRNA formulations and RNAi phenotypic effects were assessed over time. At 2 days post-spray, Sfarm transcript levels decreased by 86 ± 9.5% compared with dsGFP groups, and the subsequent incidences of mortality and wing defects were elevated in the treatment group.

CONCLUSIONS

This study characterized five genes in the WBPH developmental signaling cascade, assessed their impact on survival and wing development via RNAi, and developed a nanoparticle-dsRNA spray approach for potential field control of WBPH. © 2023 Society of Chemical Industry.

Functional characterization of tyrosine melanin genes in the white-backed planthopper and utilization of a spray-based nanoparticle-wrapped dsRNA technique for pest control

As a significant pest of rice the white-backed planthopper (WBPH) Sogatella furcifera is a focus of pest management. However, traditional chemical-based control methods risk the development of pesticide resistance as well as severe ecological repercussions. Although nanoparticle-encapsulated dsRNAs provide a promising alternative method for sustainable pest management, gene targets specific to WBPH have yet to be optimized. Genes in the tyrosine-melanin pathway impact epidermal melanization and sclerotization, two processes essential for insect development and metabolism, have been proposed as good candidate targets for pest management. Seven genes (aaNAT, black, DDC, ebony, tan, TH, and yellow-y) in this group were identified from WBPH genome and functionally characterized by using RNAi for their impact on WBPH body color, development, and mortality. Knockdown of SfDDC, Sfblack, SfaaNAT, and Sftan caused cuticles to turn black, whereas Sfyellow-y and Sfebony knockdown resulted in yellow coloration. SfTH knockdown resulted in pale-colored bodies and high mortality. Additionally, an Escherichia coli expression system for large-scale dsRNA production was coupled with star polycation nanoparticles to develop a sprayable RNAi method targeting SfTH that induced high WBPH mortality rates on rice seedlings. These findings lay the groundwork for the development of large-scale dsRNA nanoparticle sprays as a WBPH control method.

Functional characterization of developmentally critical genes in the white-backed planthopper: Efficacy of nanoparticle-based dsRNA sprays for pest control

BACKGROUND

Epidermal growth factor receptor (EGFR), zinc finger homeodomain-2 (zfh-2), Abdominal-A (Abd-A), and Abdominal-B (Abd-B) regulate the growth and development of the insect abdomen. However, their potential roles in pest control have not been fully assessed. The development of insecticide resistance to multiple chemistries in the white-backed planthopper (WBPH), a major pest of rice, has prompted interest in novel pest control approaches that are ecologically friendly. Although pest management approaches based on double-stranded RNA (dsRNA)-mediated RNA interference (RNAi) have potential, their susceptibility to degradation limits large-scale field applications. These limitations, however, can be overcome with nanoparticle-dsRNA complexes that have greater environmental stability and improved cellular uptake.

RESULTS

In this study, at 5 days post-injection, transcripts for the four gene targets were reduced relative to controls and all of the experimental groups exhibited significant phenotypic defects and increased mortality. To evaluate the potential of these gene targets for field applications, a nanocarrier-dsRNA spray delivery system was assessed for RNAi efficacy. At 11 days post-spray, significant phenotypic defects and increased mortality were observed in all experimental groups.

CONCLUSION

Taken together, the results confirm the suitability of the target genes (SfEGFR, Sfzfh-2, SfAbd-A, and SfAbd-B) for pest management and demonstrate the efficacy of the nanocarrier spray system for inducing RNAi-mediated knockdown. As such, the study lays the foundation for the further development and optimization of this technology for large-scale field applications. © 2022 Society of Chemical Industry.

A Highly Expressed Antennae Odorant-Binding Protein Involved in Recognition of Herbivore-Induced Plant Volatiles in Dastarcus helophoroides

Natural enemies such as parasitoids and parasites depend on sensitive olfactory to search for their specific hosts. Herbivore-induced plant volatiles (HIPVs) are vital components in providing host information for many natural enemies of herbivores. However, the olfactory-related proteins involved in the recognition of HIPVs are rarely reported. In this study, we established an exhaustive tissue and developmental expression profile of odorant-binding proteins (OBPs) from Dastarcus helophoroides, an essential natural enemy in the forestry ecosystem. Twenty DhelOBPs displayed various expression patterns in different organs and adult physiological states, suggesting a potential involvement in olfactory perception. In silico AlphaFold2-based modeling and molecular docking showed similar binding energies between six DhelOBPs (DhelOBP4, 5, 6, 14, 18, and 20) and HIPVs from Pinus massoniana. While in vitro fluorescence competitive binding assays showed only recombinant DhelOBP4, the most highly expressed in the antennae of emerging adults could bind to HIPVs with high binding affinities. RNAi-mediated behavioral assays indicated that DhelOBP4 was an essential functional protein for D. helophoroides adults recognizing two behaviorally attractive substances: p-cymene and γ-terpinene. Further binding conformation analyses revealed that Phe 54, Val 56, and Phe 71 might be the key binding sites for DhelOBP4 interacting with HIPVs. In conclusion, our results provide an essential molecular basis for the olfactory perception of D. helophoroides and reliable evidence for recognizing the HIPVs of natural enemies from insect OBPs' perspective.

Plant volatile ligands for male-biased MmedOBP14 stimulate orientation behavior of the parasitoid wasp Microplitis mediator

As an important class of chemosensory-associated proteins, odorant binding proteins (OBPs) play a key role in the perception of olfactory signals for insects. Parasitoid wasp Microplitis mediator relies on its sensitive olfactory system to locate host larvae of Noctuidae and Geometridae. In the present study, MmedOBP14, a male-biased OBP in M. mediator, was functionally investigated. In fluorescence competitive binding assays, the recombinant MmedOBP14 showed strong binding abilities to five plant volatiles: β-ionone, 3,4-dimethylacetophenone, 4-ethylacetophenone, acetophenone and ocimene. Homology modeling and molecular docking results indicated that the binding sites of all five ligands were similar and concentrated in the binding pocket of MmedOBP14. Except acetophenone, the remaining four ligands at 1, 10 and 100 μg/μL caused strong antennal electrophysiological responses in adults M. mediator, and males showed more obvious EAG responses to most ligands than females. In behavioral trials, males were attracted by low concentrations of MmedOBP14 ligands, whereas high doses of β-ionone and acetophenone had a repellent effect on males. Moreover, 1 μg/μL of 3,4-dimethylacetophenone showed the strongest attractiveness to female wasps. These findings suggest that MmedOBP14 may play a more important role in the perception of plant volatiles for male wasps to locate habitat, supplement nutrition and search partners.

NlugOBP8 in Nilaparvata lugens Involved in the Perception of Two Terpenoid Compounds from Rice Plant

Odorant binding proteins (OBPs) play an important role in insect peripheral olfactory systems and exploring the physiological function of OBPs could facilitate the understanding of insects' chemical communication. Here, the functional analysis of an antenna-based NlugOBP8 from brown planthopper (BPH) Nilaparvata lugens (Stål) was performed both in vitro and in vivo. Recombinant NlugOBP8 exhibited strong binding affinity to 13 out of 26 rice plant volatiles and could form a stable complex with 9 of them according to the fluorescence binding and fluorescence quenching experiments. Circular dichroism spectra demonstrated that six volatiles could give rise to significant conformational change of recombinant NlugOBP8. H-tube olfactometer bioassay confirmed that BPHs were significantly attracted by nerolidol and significantly repelled by linalool, caryophyllene oxide, and terpinolene, respectively. Antennae of dsNlugOBP8-injected BPHs exhibited significantly lower electrophysiological response to linalool and caryophyllene oxide. Moreover, the repellent responses of BPHs to these two volatiles were also impaired upon silencing NlugOBP8. These data suggest that NlugOBP8 is involved in recognizing linalool and caryophyllene oxide and provide additional target for the sustainable control of BPHs.

Binding properties of odorant-binding protein 4 from bean bug Riptortus pedestris to soybean volatiles

The bean bug Riptortus pedestris is a notorious insect pest that can damage various crops, especially soybean, in East Asia. In insects, the olfactory system plays a crucial role in host finding and feeding behaviour in which the odorant-binding proteins (OBPs) are believed to be involved in initial step in this system. In this study, we produced the R. pedestris adult antennae-expressed RpedOBP4 protein using a recombinant expression system in E. coli. Fluorescence competitive binding confirmed that RpedOBP4 has binding affinities to 7 of 20 soybean volatiles (ligands), and that a neutral condition is the best environment for it. The binding property of RpedOBP4 to these ligands was further revealed by integrating data from molecular docking, site-directed mutagenesis and ligand binding assays. This demonstrated that five amino acid residues (I30, L33, Y47, I57 and Y121) are involved in the binding process of RpedOBP4 to corresponding ligands. These findings will not only help us to more thoroughly explore the olfactory mechanism of R. pedestris during feeding on soybean, but also lead to the identification of key candidate targets for developing environmental and efficient behaviour inhibitors to prevent population expansion of R. pedestris in the future.

Two Odorant-Binding Proteins Involved in the Recognition of Sex Pheromones in Spodoptera litura Larvae

Usually, the recognition of sex pheromone signals is restricted to adult moths. Here, our behavioral assay showed that fourth-instar Spodoptera litura larvae are attracted to cabbage laced with minor sex pheromones Z9,E12-tetradecadienyl acetate (Z9,E12-14:Ac) or Z9-tetradecenyl acetate (Z9-14:Ac). Seven odorant-binding proteins (OBPs) were upregulated after exposure to Z9,E12-14:Ac, and one OBP was upregulated after exposure to Z9-14:Ac. Fluorescence competitive binding assays showed that GOBP2 and OBP7 bound to sex pheromones. RNAi treatment significantly downregulated GOBP2 and OBP7 mRNA expression by 70.37 and 63.27%, respectively. The siOBP-treated larvae were not attracted to Z9,E12-14:Ac or Z9-14:Ac, and the corresponding preference indices were significantly lower than those in siGFP-treated larvae. Therefore, we concluded that GOBP2 and OBP7 are involved in the attraction of S. litura larvae to food containing Z9,E12-14:Ac and Z9-14:Ac. These results provide an important basis for exploring the olfactory mechanisms underlying sex pheromone attraction in moth larvae.

Genome-Wide Analysis of Odorant-Binding Proteins and Chemosensory Proteins in the Bean bug Riptortus pedestris

Insects have sensitive olfactory systems to interact with environment and respond to the change in host plant conditions. Key genes in the system can be potential targets for developing new and efficient pest behaviour control methods. Riptortus pedestris is an important soybean pest in East Asia and has caused serious damage to the soybean plants in Huang-Huai-Hai region of China. However, the current treatment of pests is dominated by chemical insecticides and lacks efficient sustainable prevention and control technologies. In this study, we identified 49 putative odorant-binding proteins (OBPs) (43 were new genes) and 25 chemosensory proteins (CSPs) (17 were new genes) in R. pedestris genome. These OBP and CSP genes are clustered in highly conserved groups from other hemipteran species in phylogenetic trees. Most RpedOBPs displayed antennal-biased expression. Among the 49 RpedOBPs, 33 were significantly highly expressed in the antennae, including three male-biased and nine female-biased. While many RpedCSPs were detected both in the antennae and in non-antennal tissues, only 11 RpedCSPs displayed antennal-biased expression, in which four RpedCSPs were male-biased and five RpedCSPs were female-biased. Some OBP and CSP genes showed sex-biased expression profiles. Our results not only provide a foundation for future exploration of the functions of RpedOBPs and RpedCSPs but also aid in developing environmentally friendly insecticides in the future.

Evolutionarily conserved odorant-binding proteins participate in establishing tritrophic interactions

Attracting herbivores and their natural enemies is a standard method where plant volatiles mediate tritrophic interactions. However, it remains unknown whether the shared attraction has a shared chemosensory basis. Here we focus on the odorant-binding proteins (OBPs), a gene family integral to peripheral detection of odoriferous chemicals. Previous evidence suggests that the herbivorous beetle Monochamus alternatus and its parasitoid beetle Dastarcus helophoroides are attracted to stressed pines. In this study, (+)-fenchone, emitted by stressed pines, is found to be attracted to M. alternatus and D. helophoroides in behavioral assays. Meanwhile, two orthologous OBPs with a slower evolutionary rate, respectively, from the two insects are shown to bind with (+)-fenchone, and the attraction is abolished after RNAi. These results show the ability of evolutionarily conserved OBPs from herbivores and their enemies to detect the same plant volatiles, providing an olfactory mechanism of chemical signals–mediated tritrophic relationships.

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Monochamus alternatus and Dastarcus helophoroides are attracted to (+)-fenchone from host pines

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They harbor evolutionarily conserved odorant-binding proteins (OBPs)

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One pair of the conserved OBPs can bind with (+)-fenchone

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The behavioral preference is lost upon RNAi knockdown of the OBPs

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.

The Entomopathogenic Fungus Metarhizium anisopliae Affects Feeding Preference of Sogatella furcifera and Its Potential Targets’ Identification

The rice planthopper Sogatella furcifera is a unique vector of the southern rice black-streaked dwarf virus (SRBSDV). The feeding behavior of S. furcifera should directly affect the diffusion of this virus. In this study, we noted that the infection of Metarhizium anisopliae CQMa421 on S. furcifera disturbed the feeding behavior of this pest to SRBSDV-infected rice, from preference to non-preference. Then, we further investigated the potential targets of M. anisopliae CQMa421 on the feeding behavior of S. furcifera after 0 h, 24 h and 48 h of infection by transcriptomic analysis via Illumina deep sequencing. A total of 93.27 GB of data was collected after sequencing, from which 91,125 unigenes were annotated, including 75 newly annotated genes. There were 1380 vs. 2187 and 137 vs. 106 upregulated and downregulated differentially expressed genes (DEGs) detected at 24 h and 48 h, respectively. The biological functions and associated metabolic processes of these genes were determined with the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The results suggested that major of DEGs are involved in energy metabolism, biosynthesis, immune response, the FoxO signaling pathway, the MAPK signaling pathway and apoptosis in response to the fungal infection. Noteworthily, several olfactory-related genes, including odorant receptors and odorant binding proteins, were screened from these differentially expressed genes, which played critical roles in regulating the olfactory behavior of insects. Taken together, these results provide new insights for understanding the molecular mechanisms underlying fungus and host insect interaction, especially for olfactory behavior regulated by fungus.

Odorant binding protein 3 is associated with nitenpyram and sulfoxaflor resistance in Nilaparvata lugens

Odorant binding protein (OBP) can interact with small-molecule compounds insecticides and thereby modulate variation in insecticide susceptibility in insects. However, the regulatory mechanism of OBP-mediated insecticide resistance in Nilaparvata lugens, a destructive rice pest in Asia, remains unclear. Here, we explored the role of NlOBP3 in the resistance of N. lugens to nitenpyram and sulfoxaflor. The results showed that NlOBP3 was overexpressed in association with nitenpyram and sulfoxaflor resistance, and NlOBP3 silencing significantly increased the mortality of N. lugens to nitenpyram and sulfoxaflor, suggesting that NlOBP3 may be associated with nitenpyram and sulfoxaflor resistance in N. lugens. OBP localization revealed that NlOBP3 was highly expressed in all nymph stages and was enriched in the antennae, legs, body wall, and fat body. RT-qPCR analyses showed that the mRNA levels of NlOBP3 were significantly affected by nitenpyram and sulfoxaflor. Additionally, molecular docking predicted that there were multiple binding sites that may played key roles in the binding of NlOBP3 with nitenpyram and sulfoxaflor. The current study identifies a previously undescribed mechanism of insecticide resistance in N. lugens, showing that NlOBP3 is likely to be involved in the evolution of nitenpyram and sulfoxaflor resistance in N. lugens.

The molecular identification, odor binding characterization, and immunolocalization of odorant-binding proteins in Liriomyza trifolii

The Liriomyza trifolii is a highly invasive polyphagia pest. Understanding the physiological functions of odorant binding proteins (OBPs) in the chemical communication of L. trifolii can lead to effective pest management strategies. Seven full-length OBPs were identified by transcriptome screening of L. trifolii adults. Bioinformatics analyses classified the seven OBPs into two subfamilies (six classic OBPs, one minus-C OBP). The analysis of their expression in different development stages revealed that LtriOBP5 was highly expressed in the larval stage, LtriOBP4 in the pupa stage, and LtriOBP1, 2, 3, 6, 7 in the adult stage; the expression levels were higher in male adults than in females. The analysis of different tissues showed high expression of LtriOBP1, 3, 6, 7 in the antennae, which were selected for in vitro purification. To explore the ligand compounds of OBPs, fluorescence competitive binding experiments were performed. Immunofluorescence localization revealed that LtriOBP1, 3, 6, 7 showed strong binding abilities to plant volatiles and were located in the antennae, implying that LtriOBP1, 3, 6, 7 may play key roles in olfaction, such as host location. LtriOBP6 and LtriOBP7 had strong binding abilities to specific herbivore-induced plant volatiles, suggesting LtriOBP6 and LtriOBP7 may also play critical roles in chemoreception. This study provides preliminary exploration of the olfactory perception mechanism of L. trifolii, which can be used as a basis to design insect behavior regulators and develop highly effective insecticides using mixture of ligands and known pesticides.

Ligand-binding properties of odorant-binding protein 6 in Athetis lepigone to sex pheromones and maize volatiles

BACKGROUND

Athetis lepigone, a noctuid moth feeding on more than 30 different crops worldwide, has evolved a sophisticated, sensitive, and specific chemosensory system to detect and discriminate exogenous chemicals. Odorant-binding proteins (OBPs) are the most important agent in insect chemosensory systems to be explored as an alternative target for environmentally friendly approaches to pest management.

RESULTS

To investigate the olfactory function of A. lepigone OBPs (AlepOBPs), AlepOBP6 was identified and expressed in Escherichia coli. The binding affinity of the recombinant OBP to 20 different ligands was then examined using a competitive binding approach. The results revealed that AlepOBP6 can bind to two sex pheromones and ten maize volatiles, and its conformation stability is pH dependent. We also carried out a structure-function study using different molecular approaches, including structure modeling, molecular docking, and a mutation functional assay to identify amino acid residues (M39, V68, W106, Q107, and Y114) involved in the binding of AlepOBP6 to both sex pheromones and maize volatiles in A. lepigone.

CONCLUSION

These results suggest that AlepOBP6 is likely involved in mediating the responses of A. lepigone to sex pheromones and maize volatiles, which may play a pivotal function in mating, feeding, and oviposition behaviors. This study not only provides new insight into the binding mechanism of OBPs to sex pheromones and host volatiles in moths, but also contributes to the discovery of novel target candidates for developing efficient behavior disruptors to control A. lepigone in the future. © 2021 Society of Chemical Industry.

A cytorhabdovirus-based expression vector in Nilaparvata lugens, Laodelphax striatellus, and Sogatella furcifera

The brown planthopper (BPH, Nilaparvata lugens), the small brown planthopper (SBPH, Laodelphax striatellus), and the white-backed planthopper (WBPH, Sogatella furcifera) are problematic insect pests and cause severe yield losses through phloem sap-sucking and virus transmission. Barley yellow striate mosaic virus (BYSMV), a plant cytorhabdovirus, has been developed as versatile expression platforms in SBPHs and cereal plants. However, bio-safe overexpression vectors based on recombinant BYSMV (rBYSMV) remain to be developed and applied to the three kinds of planthoppers. Here, we found that rBYSMV was able to infect SBPHs, BPHs and WBPHs through microinjection with crude extracts from rBYSMV-infected barley leaves. To ensure bio-safety of the rBYSMV vectors, we generated an rBYSMV mutant by deleting the accessory protein P3, a putative viral movement protein. As expected, the resulting mutant abolished viral systemic infection in barley plants but had no effects on BYSMV infectivity in insect vectors. Subsequently, we used the modified rBYSMV vector to overexpress iron transport peptide (ITP) in the three kinds of planthoppers and revealed the potential functions of ITP. Overall, our results provide bio-safe overexpression platforms to facilitate functional genomics studies of planthoppers.

Expression and functional characterization of odorant-binding protein genes in the endoparasitic wasp Cotesia vestalis

Odorant-binding proteins (OBPs) are crucial in insect's olfactory perception, which participate in the initial step of odorant molecules transporting from the external environment to olfactory receptor neurons. To better understand the roles for OBPs in olfactory perception in Cotesia vestalis, a solitary larval endoparasitoid of diamondback moth, Plutella xylostella, we have comprehensively screened the genome of C. vestalis, and obtained 20 CvesOBPs, including 18 classic OBPs and two minus-C OBPs. Motif-pattern analysis indicates that the motifs of C. vestalis OBPs are highly conserved in Hymenoptera. The results of tissue expression analysis show that five OBPs (CvesOBP1/11/12/14/16) are highly expressed in male antennae, whereas six other OBP genes (CvesOBP7/8/13/17/18/19) are significantly transcriptionally enriched in female antennae. The results of RNA interference experiments for three most highly expressed OBP genes (CvesOBP17/18/19) in female antennae demonstrate that they are likely involved in parasitic processes of female wasps, as the wasps take a longer time to target the hosts when they are knocked down.

Chemosensory genes in the head of Spodoptera litura larvae

The tobacco cutworm Spodoptera litura (Lepidoptera: Noctuidae) is a polyphagous pest with a highly selective and sensitive chemosensory system involved in complex physiological behaviors such as searching for food sources, feeding, courtship, and oviposition. However, effective management strategies for controlling the insect pest populations under threshold levels are lacking. Therefore, there is an urgent need to formulate eco-friendly pest control strategies based on the disruption of the insect chemosensory system. In this study, we identified 158 putative chemosensory genes based on transcriptomic and genomic data for S. litura, including 45 odorant-binding proteins (OBPs, nine were new), 23 chemosensory proteins (CSPs), 60 odorant receptors (ORs, three were new), and 30 gustatory receptors (GRs, three were new), a number higher than those reported by previous transcriptome studies. Subsequently, we constructed phylogenetic trees based on these genes in moths and analyzed the dynamic expression of various genes in head capsules across larval instars using quantitative real-time polymerase chain reaction. Nine genes-SlitOBP8, SlitOBP9, SlitOBP25, SlitCSP1, SlitCSP7, SlitCSP18, SlitOR34, SlitGR240, and SlitGR242-were highly expressed in the heads of 3- to 5-day-old S. litura larvae. The genes differentially expressed in olfactory organs during larval development might play crucial roles in the chemosensory system of S. litura larvae. Our findings substantially expand the gene inventory for S. litura and present potential target genes for further studies on larval feeding in S. litura.

An odorant-binding protein of Asian citrus psyllid, Diaphorina citri, participates in the response of host plant volatiles

BACKGROUND

Odorant-binding proteins (OBPs) in insects contribute to the sensitivity of the olfactory system and connect external odorants to olfactory receptor neurons. Determination of the chemosensory functions in Diaphorina citri, a vector of the citrus Huanglongbing pathogen, may help in developing a potential target for pest management.

RESULTS

Diaphorina citri showed dose-dependent electroantennogram recording (EAG) responses to 12 host plant volatiles. A two-choice behavioral trap experiment showed that four compounds (methyl salicylate, linalool, citral and R-(+)-limonene) that elicited high EAG responses also had significant attraction to adults. The expression profiles induced by these compounds were detected in nine OBP genes, DcitOBP1-9. DcitOBP3, DcitOBP6 and DcitOBP7 commonly showed significant upregulation or downregulation compared with the control. Microscale thermophoresis (MST) showed that the recombinant protein DcitOBP7 had high in vitro binding affinities (K_d  < 10 μm) to methyl salicylate, linalool and R-(+)-limonene, and moderate binding affinity to citral with a K_d value of 15.95 μm. Furthermore, RNA interference (RNAi)-suppressed messenger RNA (mRNA) expression of DcitOBP7 resulted in a significant reduction in EAG activity and in adult D. citri behavioral responses to tested volatiles and the preferred host, Murraya paniculata. The hydrophilic residue Arg107 of DcitOBP7 may have a key role in binding odorants via formation of hydrogen bonds.

CONCLUSION

These results show that DcitOBP7 plays an important role in the olfactory response. This finding may provide new insight into the functions of OBP families in D. citri and aid in the development of safe strategies for managing D. citri populations. © 2021 Society of Chemical Industry.

Identification and characterization of soluble binding proteins associated with host foraging in the parasitoid wasp Diachasmimorpha longicaudata

The communication and reproduction of insects are driven by chemical sensing. During this process, chemical compounds are transported across the sensillum lymph to the sensory neurons assisted by different types of soluble binding proteins: odorant-binding proteins (OBPs); chemosensory proteins (CSPs); some members of ML-family proteins (MD-2 (myeloid differentiation factor-2)-related Lipid-recognition), also known as NPC2-like proteins. Potential transcripts involved in chemosensing were identified by an in silico analysis of whole-body female and male transcriptomes of the parasitic wasp Diachasmimorpha longicaudata. This analysis facilitated the characterization of fourteen OBPs (all belonging to the Classic type), seven CSPs (and two possible isoforms), and four NPC2-like proteins. A differential expression analysis by qPCR showed that eleven of these proteins (CSPs 2 and 8, OBPs 2, 3, 4, 5, 6, 9, 10, and 11, and NPC2b) were over-expressed in female antenna and two (CSP 1 and OBP 12) in the body without antennae. Foraging behavior trials (linked to RNA interference) suggest that OBPs 9, 10, and 11 are potentially involved in the female orientation to chemical cues associated with the host. OBP 12 seems to be related to physiological processes of female longevity regulation. In addition, transcriptional silencing of CSP 3 showed that this protein is potentially associated with the regulation of foraging behavior. This study supports the hypothesis that soluble binding proteins are potentially linked to fundamental physiological processes and behaviors in D. longicaudata. The results obtained here contribute useful information to increase the parasitoid performance as a biological control agent of fruit fly pest species.

Two carboxylesterase genes in Plutella xylostella associated with sex pheromones and plant volatiles degradation

BACKGROUND

Carboxyl/cholinesterases (CCEs) are thought to play a pivotal role in the degradation of sex pheromones and plant-derived odorants in insects, but their exact biochemistry and physiological functions remain unclear.

RESULTS

In this study, two paralogous antennae-enriched CCEs from Plutella xylostella (PxylCCE16a and 16c) were identified and functionally characterized. High-purity protein preparations of active recombinant PxylCCE16a and 16c have been obtained from Sf9 insect cells by Ni²⁺ affinity purification. Our results revealed that the purified recombinant PxylCCE016c is able to degrade two sex pheromone components Z9-14:Ac and Z11-16:Ac at 27.64 ± 0.79% and 24.40 ± 3.07%, respectively, while PxylCCE016a presented relatively lower activity. Additionally, a similar difference in activity was measured in plant-derived odorants. Furthermore, both CCEs displayed obvious preferences for the two sex pheromone components, especially on Z11-16:Ac (K_m values are in the range 7.82-45.06 μmol L^-1 ) which much lower than plant odorants (K_m values are in the range 1290-4030 μmol L^-1 ). Furthermore, the activity of the two newly identified CCEs is pH-dependent. The activity at pH 6.5 is obviously higher than that at pH 5.0. Interestingly, only PxylCCE016c can be inhibited by a common esterase inhibitor triphenyl phosphate (TPP) with LC₅₀ of 1570 ± 520 μmol L^-1 .

CONCLUSION

PxylCCE16c plays a more essential role in odorant degradation than PxylCCE16a. Moreover, the current study provides novel potential pesticide targets for the notorious moth Plutella xylostella. © 2021 Society of Chemical Industry.

Silencing the odorant coreceptor (Orco) disrupts sex pheromonal communication and feeding responses in Blattella germanica: toward an alternative target for controlling insect-transmitted human diseases

BACKGROUND

The German cockroach, Blattella germanica, is one of the most severe pests of urban and rural areas. High-throughput genetic screening approaches indicate that the olfactory system of this pest is extremely powerful because it has an extensive array of olfactory receptor genes compared with many other insect species. Several of these genes have been identified previously, but their functions have not yet been characterized.

RESULTS

This study describes the sequence of five transcriptomes of B. germanica adult male antennae, female antennae, maxillary palps, legs, and fifth-instar nymph antennae to investigate expression patterns of odorant receptors (ORs). Approximately 90% of ORs were found to be the most highly expressed genes in adult or nymph antennae. Additionally, every OR requires an odorant co-receptor (Orco) to become fully functional, and this was selected and successfully inhibited by injection of the corresponding double-stranded (ds)RNA targeting the Orco. A strong RNA interference (RNAi) effect was observed in which > 75% of Orco messenger RNA (mRNA) was clearly suppressed after 72 h of treatment. Olfactory behavioral assays showed that Orco-impaired B. germanica respond more slowly and show less attraction to one volatile sex pheromone and food resources compared with a control group.

CONCLUSION

The results show that Orco plays a pivotal role in both sex pheromone and food-seeking olfactory processes, and provide an alternative genetic technique for controlling this urban pest species by olfactory disruption. © 2020 Society of Chemical Industry.

Transcriptome Characterization and Expression Analysis of Chemosensory Genes in Chilo sacchariphagus (Lepidoptera Crambidae), a Key Pest of Sugarcane

Insect chemoreception involves many families of genes, including odourant/pheromone binding proteins (OBP/PBPs), chemosensory proteins (CSPs), odourant receptors (ORs), ionotropic receptors (IRs), and sensory neuron membrane proteins (SNMPs), which play irreplaceable roles in mediating insect behaviors such as host location, foraging, mating, oviposition, and avoidance of danger. However, little is known about the molecular mechanism of olfactory reception in Chilo sacchariphagus, which is a major pest of sugarcane. A set of 72 candidate chemosensory genes, including 31 OBPs/PBPs, 15 CSPs, 11 ORs, 13 IRs, and two SNMPs, were identified in four transcriptomes from different tissues and genders of C. sacchariphagus. Phylogenetic analysis was conducted on gene families and paralogs from other model insect species. Quantitative real-time PCR (qRT-PCR) showed that most of these chemosensory genes exhibited antennae-biased expression, but some had high expression in bodies. Most of the identified chemosensory genes were likely involved in chemoreception. This study provides a molecular foundation for the function of chemosensory proteins, and an opportunity for understanding how C. sacchariphagus behaviors are mediated via chemical cues. This research might facilitate the discovery of novel strategies for pest management in agricultural ecosystems.

Functional characteristic analysis of three odorant-binding proteins from the sweet potato weevil (Cylas formicarius) in the perception of sex pheromones and host plant volatiles

BACKGROUND

The sweet potato weevil, Cylas formicarius, is the most serious pest of sweet potato worldwide. The molecular mechanism of sex pheromone recognition in C. formicarius has not been reported. Odorant-binding proteins (OBPs) play a critical role in selectively binding and transporting pheromones or other odors to the surface of olfactory receptor neurons through the aqueous sensillar lymph, therefore the function of sweet potato OBPs is worth studying.

RESULTS

Herein, the CforOBP1-3 genes encoding three classical OBPs were cloned in C. formicarius by reverse transcription-polymerase chain reaction. Phylogenetic analysis showed that CforOBP1-3 were homologous genes, but the relationship between CforOBP2 and CforOBP3 was closest among the three genes. In addition, real-time quantitative reverse transcription-polymerase chain reaction (qRT-PCR) assays demonstrated that the expression of CforOBP1 was higher in the antennae and legs of female and male insects, while CforOBP2 and CforOBP3 were mainly expressed in the antennae of male insects. The fluorescent competitive binding assay results indicated that CforOBP1-3 had strong binding affinities to sex pheromones and other tested ligands. Finally, the mRNA expression of CforOBP1-3 was successfully inhibited by RNA interference, and in vivo behavioral experiments showed that CforOBP1-3-deficient C. formicarius was partly anosmic and lost some of its ability to locate sex pheromones and host plant volatiles.

CONCLUSION

These results suggested that CforOBP1 was shown to be involved in the process of weevils feeding and finding sweet potato, and CforOBP2-3 were mainly involved in the mating behavior of adult male weevils.

Expression, Affinity, and Functional Characterization of the Specific Binding of Two Putative Pheromone-Binding Proteins in the Omnivorous German Cockroach Blattella germanica

The German cockroach Blattella germanica (L.) is an important pest in medical, veterinary, and public health. Studies on the olfaction mechanism of hemimetabolous insects have rarely been reported, especially in cockroaches. Pheromone-binding proteins (PBPs) play a vital role in insect sex pheromone recognition, which solubilize and carry the hydrophobic pheromonal compounds through the antennal lymph to receptors. In this study, two potential PBPs (BgerOBP26 and BgerOBP40) were identified on the basis of their biased expression in male antennae using tissue transcriptome data and verified by the quantitative real-time polymerase chain reaction approach. We then expressed and purified the two identified odorant-binding proteins (OBPs) using the Escherichia coli expression system and affinity purification. In vitro binding studies showed that the two OBPs display stronger binding affinities to the female volatile sex pheromone blattellaquinone than to its analogues and contact sex pheromone components. Finally, three-dimensional modeling of the two OBPs and dock conformation with sex pheromone molecules showed BgerOBP26 has a larger odorant cavity and more conservative active amino acid residues than BgerOBP40. These results illuminated the binding characteristics of potential PBPs of B. germanica, which could lay the groundwork for improved understanding of many aspects of the chemical ecology of B. germanica. Moreover, this information complements the understanding of the olfactory molecular mechanism in cockroaches and provides potential gene targets for B. germanica control.

Organophosphorus insecticide interacts with the pheromone-binding proteins of Athetis lepigone: Implication for olfactory dysfunction

Athetis lepigone is one of the most severe polyphagous pests, and it has developed resistance to different chemical insecticides. Insects primarily rely on the olfactory system to recognize various environmental chemicals, including xenobiotics such as insecticides. Here, we expressed two A. lepigone pheromone-binding proteins (AlepPBP2 and AlepPBP3), and observed they had higher binding affinities to phoxim than other insecticides, with Ki was 3.30 ± 0.38 μM and 3.27 ± 0.10 μM, respectively. Molecular dynamics simulation, binding mode analysis, and computational alanine scanning showed that six residues (Phe15, Phe39, Ile55, Leu65, Ile97, and Phe122) of AlepPBP2 and three residues (Phe12, Ile52, and Ile134) of AlepPBP3 maybe as potential residues that can change protein ability to bind an organophosphorus insecticide phoxim. Then, we used site-directed mutagenesis assay to mutate these residues into alanine, respectively. Subsequently, the binding assays displayed that Phe15, Phe39, and Ile97 of AlepPBP2, Phe12 and Ile134 of AlepPBP3 caused a significant decrease of AlepPBPs binding ability to phoxim, suggesting they should play crucial roles in the AlepPBPs/phoxim interactions. Our findings could further advance in using PBPs as unique targets to design and develop precise and environmentally-friendly pest control agents with high insecticidal potential using a computer-aided drug design (CADD) approach.

Odorant-binding proteins and chemosensory proteins potentially involved in host plant recognition in the Asian citrus psyllid, Diaphorina citri

BACKGROUND

Odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) are two families of small water-soluble proteins involved in odor detection and subsequent signal transmission. Determination of their binding mechanisms and specificity towards different odorants is important for developing OBPs/CSPs as targets in pest control management.

RESULTS

We re-annotated genes encoding putative OBPs and CSPs in the Asian citrus psyllid (Diaphorina citri) draft genome using various bioinformatic tools. Genes encoding nine OBPs (seven Classic and two Plus-C) and 12 CSPs were identified, consistent with our previous transcriptomic results. Tissue-specific and developmental expression analyses suggested that genes encoding six OBPs and four CSPs were predominantly expressed in antennae, and displayed various expression patterns in different development stages, suggesting potential involvement in olfactory perception. Competitive fluorescence binding assays with 13 candidate ligands, including known host plant volatiles, sex pheromone components and repellents, showed that DcitOBP3 could bind to various odorants, whereas DcitOBP6, 8 and 9 bound specifically to host plant terpenoids. DcitCSP1 and 12 could also bind to certain terpenoids with high binding specificity.

CONCLUSION

OBP- and CSP-encoding genes were systematically identified by annotating the draft D. citri genome and those potentially involved in odorant detection and signal transmission were identified by analyzing their tissue-expression profiles and odorant-binding affinities, particularly to the peripheral molecular perception of host plant terpenoids. The identified genes may provide potential targets for efficient pest control. © 2020 Society of Chemical Industry.

Structural basis of quinolone derivatives, inhibition of type I and II topoisomerases and inquiry into the relevance of bioactivity in odd or even branches with molecular docking study

The structural modification of quinolone derivatives has been a hot spot in recent years, especially the modification of the N-1 position, which is the part that this article focuses on. In this paper, series of synthesized quinoline quaternary ammonium salts with odd and even carbon number alkyl groups in N-1 position were used to explain the influence of the alkyl side chain on activity. With respect to all the recently synthesized twenty products, the biological activity results exhibited significant antitumor and antibacterial activity with obvious differences in the target alkyliodine substituted compounds and the antibacterial activities apparently had the prominent odd-carbon number predominance. Compound 8-((4-(benzyloxy)phenyl)amino)-7-(ethoxycarbonyl)-5-propyl-[1,3]dioxolo[4,5-g]quinolin-5-ium (4d) was found to be the most potent derivative with IC₅₀ values of 4 ± 0.88, 4 ± 0.42, 14±1.96, and 32±3.66 against A-549, Hela, SGC-7901, and L-02 cells, respectively, stronger than the positive control 5-FU and MTX. Furthermore, it had the most potent bacterial inhibitory activity of MIC value against E. coli (ATCC 29213) and Staphylococcus aureus (ATCC 8739) at 3.125 nmol mL⁻¹. With respect to molecular simulations, in order to illustrate the possible mechanism of the difference between the series of compounds in the even or odd carbon chain alkyliodine substitution, this paper simulated the conceivable mode and explained the main interactions. Finally, we could find that the position and proportion of hydrogen bonds and other interactions in each series were regarded as the main reasons for this difference in activity.

Odorant Binding Proteins and Chemosensory Proteins in Episyrphus balteatus (Diptera: Syrphidae): Molecular Cloning, Expression Profiling, and Gene Evolution

Aphidophagous syrphids (Diptera: Syrphidae) are important insects in agroecosystems for pollination and biological control. Insect chemoreception is essential for these processes and for insect survival and reproduction; however, molecular determinants is not well understood for these beneficial insects. Here, we used recent transcriptome data for the common hoverfly, Episyrphus balteatus, to characterize key molecular components of chemoreception: odorant-binding proteins (OBPs) and chemosensory proteins (CSPs). Six EbalCSPs and 44 EbalOBPs were cloned from this species, and sequence analysis showed that most share the characteristic hallmarks of their protein family, including a signal peptide and conserved cysteine signature. Some regular patterns and key conserved motifs of OBPs and CSPs in Diptera were identified using the online tool MEME. Motifs were also compared among the three OBP subgroups. Quantitative real-time PCR (qRT-PCR) showed that most of these chemosensory genes were expressed in chemosensory organs, suggesting these genes have chemoreceptive functions. An overall comparison of the Ka/Ks values of orthologous genes in E. balteatus and another predatory hoverfly species to analyze the evolution of these olfactory genes showed that OBPs and CSPs are under strong purifying selection. Overall, our results provide a molecular basis for further exploring the chemosensory mechanisms of E. balteatus, and consequently, may help us to understand the tritrophic interactions among plants, herbivorous insects, and natural enemies.

Characterization of MaltOBP1, a Minus-C Odorant-Binding Protein, From the Japanese Pine Sawyer Beetle, Monochamus alternatus Hope (Coleoptera: Cerambycidae)

Insect Odorant-Binding Proteins (OBPs) play crucial roles in the discrimination, binding and transportation of odorants. Herein, the full-length cDNA sequence of Minus-C OBP1 (MaltOBP1) from the Japanese pine sawyer beetle, Monochamus alternatus, was cloned by 3′ and 5′ RACE-PCR and analyzed. The results showed that MaltOBP1 contains a 435 bp open reading frame (ORF) that encodes 144 amino acids, including a 21-amino acid signal peptide at the N-terminus. The matured MaltOBP1 protein possesses a predicted molecular weight of about 14 kDa and consists of six α-helices, creating an open binding pocket, and two disulfide bridges. Immunoblotting results showed that MaltOBP1 was most highly expressed in antennae in both sexes, followed by wings and legs. Fluorescence assays demonstrated that MaltOBP1 protein exhibited high binding affinity with (R)-(+)-α-pinene, (−)-β-pinene, trans-caryophyllene, (R)-(+)-limonene and (–)-verbenone, which are the main volatile compounds of the pine tree. Our combined results suggest that MaltOBP1 plays a role in host seeking behavior in M. alternatus.

Molecular and Functional Characterization of One Odorant-Binding Protein Gene OBP3 in Bemisia tabaci (Hemiptera: Aleyrodidae)

Odorant binding proteins (OBPs) of insects play a critical role in chemical perceptions and choice of insect host plant. Bemisia tabaci is a notorious insect pest which can damage more than 600 plant species. In order to explore functions of OBPs in B. tabaci, here we investigated binding characteristics and function of odorant-binding protein 3 in B. tabaci (BtabOBP3). The results indicated that BtabOBP3 shows highly similar sequence with OBPs of other insects, including the typical signature motif of six cysteines. The recombinant BtabOBP3 protein was obtained, and the evaluation of binding affinities to tested volatiles of host plant was conducted, then the results indicated that β-ionone had significantly higher binding to BtabOBP3 among other tested plant volatiles. Furthermore, silencing of BtabOBP3 significantly altered choice behavior of B. tabaci to β-ionone. In conclusion, it has been demonstrated that BtabOBP3 exerts function as one carrier of β-ionone and the results could be contributed to reveal the mechanisms of choosing host plant in B. tabaci.

Identification and comparative expression profiles of chemosensory genes in major chemoreception organs of a notorious pests, Laodelphax striatellus

The small brown planthopper, Laodelphax striatellus (Stål) (SBPH), is a notorious rice pest in East Asia and damages the host by feeding on the phloem and transmitting virus particles. Although SBPH relies on chemosensory perception for seeking the host, courtship, selecting oviposition sites and spreading virus particles, a systematic study of chemosensory genes in SBPH is lacking. In this study, we identified multi-gene chemosensory families from the transcriptome of SBPH olfactory organs and analyzed their expression patterns in male and female tissues. Among the chemosensory genes, 14 odorant-binding proteins (OBPs), 12 chemosensory proteins (CSPs), 7 sensory neuron membrane proteins (SNMPs) and 95 odorant receptors (ORs) were identified and annotated in SBPH olfactory organs. Based on expression profile and phylogenetic analysis, LstrOBP1, 2, 5, 6, 7, 10, LstrSNMP1, and most LstrORs showed an antennae-enriched expression pattern, which suggests an olfactory role for these genes. Relative expression of LstrOBPs was validated by quantitative real-time PCR. Our findings provide the genetic information for disrupting the feeding behavior of SBPH, which is essential for developing eco-friendly pest management technologies.

Identification and expression analysis of odorant binding proteins and chemosensory proteins from dissected antennae and mouthparts of the rice bug Leptocorisa acuta

The rice bug, Leptocorisa acuta (Tunberg) (Hemiptera: Alydidae), is a notorious pest in Asia, and it is significantly attracted by the volatiles derived from host plants. However, it remains unknown how L. acuta recognizes host volatile compounds at the molecular level. Odorant-binding proteins (OBPs) and chemosensory proteins (CSPs) are thought to be responsible for the initial biochemical recognition during olfactory perception. Here, we followed the RNA Sequencing (RNA-Seq) approach to identify candidate genes encoding OBPs and CSPs from dissected antennae and mouthparts of L. acuta. In total, 26 unigenes were identified coding for OBPs (22 Classic OBPs and four Plus-C OBPs), and 17 unigenes coding for CSPs. Real-time quantitative PCR (RT-qPCR) revealed that 11 OBPs (LacuOBP1, 5, 6, 7, 9, 11, 13, 14, 17, 20 and 23) and nine CSPs (LacuCSP2, 3, 4, 5, 6, 8, 9, 10 and 12) were predominantly expressed in antennae, indicating that they might be essential for detection of general odorants and pheromones. Among these antennae-predominantly expressed genes, LacuOBP11 and LacuOBP13 showed male-biased expression and therefore may play crucial roles in the detection of sex pheromones. Seven LacuOBPs (LacuOBP4, 8, 10, 12, 21, 25 and 26) and two CSPs (LacuCSP7 and LacuOBP11) were predominantly expressed in mouthparts, suggesting that these genes might be involved in taste perception. Our work provides a starting point to facilitate functional study of these OBPs and CSPs in L. acuta at the molecular level in the future.