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

Molecular Characterization and Functional Analysis of Odorant-Binding Proteins in Ectropis grisescens

Insect odorant-binding proteins (OBPs) are promising molecular targets for developing novel pest management strategies by modulating chemoreception-driven behaviors. The tea gray geometrid Ectropis grisescens (Lepidoptera, Geometridae) is a major pest in tea plantations, causing substantial economic losses in China. In this study, we identified 18 OBPs from E. grisescens antennal transcriptome. All of the encoded proteins possessed N-terminal signal peptides and conserved cysteine residues, behaviors which are characteristic of insect OBPs. Phylogenetic analysis categorized these proteins into plus-C, minus-C, and classic OBP subfamilies. MEME motif analysis identified conserved sequence features potentially involved in odor detection. Tissue- and sex-specific expression profiling showed that EgriGOBP1-2, OBP3, OBP8, and OBP13 were highly expressed in the antennae of both sexes, suggesting roles in olfactory communication. Among them, EgriGOBP1-2, OBP3, and OBP13 exhibited similar expression levels between males and females, while other EgriOBPs were predominantly expressed in the legs, wings, or other tissues, indicating additional physiological functions beyond chemoreception. To investigate functional specificity, we selected antenna-enriched EgriGOBP2 for ligand-binding analysis. Fluorescence binding assays demonstrated that EgriGOBP2 exhibited broad binding affinity toward 8 of 12 host volatiles and 11 of 12 plant essential oil-derived volatiles. These combined findings lay the foundation for mechanistic studies of chemical recognition in E. grisescens and provide insights into the development of ecologically friendly pest control alternatives.

Binding Properties of the General Odorant-Binding Protein GOBP2 to Herbicides and Insecticides in Spodoptera litura

We previously reported that the general odorant-binding protein GOBP2 enhances chlorpyrifos tolerance in Spodoptera litura by perceiving the herbicides. However, the direct interaction between GOBP2 and pesticides remains unknown. Herein, we verified the effect of the direct binding of GOBP2 to pesticides on the herbicide-induced insecticide tolerance in S. litura. Fluorescence competitive binding assays indicated that GOBP2 exhibits high binding affinities to the herbicide trifluralin and the insecticides indoxacarb, chlorpyrifos, and fipronil, with Ki values ranging from 1.95 to 13.01 μM. Moreover, Ala136 and Thr30 were determined as the key binding sites of GOBP2 to the pesticides through molecular docking and site-directed mutagenesis. Finally, the knockdown of GOBP2 significantly increased the larval susceptibility to trifluralin and three types of insecticides. Our findings provide a valuable reference for the further exploration of the molecular mechanisms underlying herbicide-induced insecticide tolerance in S. litura, laying the foundation for innovative pest management strategies.

Comparative analyses of odorant binding protein orthologues in three sympatric Tomicus bark beetles provide insights into functional differentiation of OBPs to ecologically relevant odorants and insecticides

Three Tomicus bark beetles (T. yunnanensis, T. brevipilosus and T. minor) coexist in the trunks of Pinus yunnanensis but possess relatively independent spatio-temporal ecological niches. This makes them become a good case for addressing functional differentiation of chemosensory-related proteins among closely related species in odorant recognition and insecticide sequestering. In this study, we used odorant binding protein (OBP) orthologues highly expressed in antennae to illustrate this question. We first identified 33, 35 and 34 OBPs from T. yunnanensis, T. brevipilosus and T. minor, respectively, with 33 groups of OBP orthologues. Sequence and phylogenetic analyses revealed the conservation and differences of OBP orthologues across three Tomicus beetles. Expression profiles revealed that the majority of Tomicus OBPs were abundantly expressed in antennae where 11 groups of OBP orthologues shared a significantly antenna-enriched distribution. Four groups of antennal OBP orthologues (OBP2, OBP9, OBP10 and OBP16 totaling 12 genes) presented diverse ligand-binding properties, responding differently to five classes of ecologically relevant odorants as well as various insecticides. In particular, OBP orthologues were tuned differentially to host and non-host odorants, and chlorpyrifos was identified as the best ligand for 12 Tomicus OBPs. Our study thus sheds light on functional conservation and divergence of OBP orthologues among three sympatric Tomicus bark beetles, possibly as an implication for the early or late of host colonization, ecological niche differences and the strong habitat adaptation.

Mechanistic exploration of odorant binding protein-mediated chlorpyrifos resistance in Nilaparvata lugens: Insights from insecticide sequestration and transcriptional regulation

The effectiveness and sustainable application of insecticides are severely threatened by the rapid evolution of resistance in agricultural pests. Recent research indicates that odorant binding proteins (OBPs) may be involved in facilitating insecticide resistance, while the specific mechanisms remain poorly understood. Herein, 11 OBPs were identified from Nilaparvata lugens. Among them, OBP5 exhibited high and specific expression in the head, and showed constitutive overexpression in the chlorpyrifos-resistant strain. Knockdown of OBP5 notably restored susceptibility to chlorpyrifos in N. lugens, while overexpression of OBP5 in Escherichia coli significantly enhanced bacterial tolerance to chlorpyrifos. Fluorescence competitive binding assay confirmed the strong binding affinities of OBP5 to chlorpyrifos and its active metabolite chlorpyrifos-oxon. Molecular docking studies proposed a critical interacting amino acid (Lys147) in the binding site, which was further validated by comparative binding studies between wildtype OBP5 and the mutated protein OBP5K147A. Furthermore, Lim1β that also presented overexpression pattern in the resistant strain, was found to regulate expression of OBP5 through a dual-luciferase reporter assay. Our findings demonstrate that the overexpression of OBP5 contributes to chlorpyrifos resistance by binding and sequestering the insecticides, shedding light on the sequestration resistance mechanism conferred by OBPs and offering potential targets for resistance management.

Three odorant-binding proteins of small hive beetles, Aethina tumida, participate in the response of bee colony volatiles

Aethina tumida (small hive beetle, SHB) is a rapidly spreading invasive parasite of bee colonies. The olfactory system plays a key role in insect behavior, and odorant-binding proteins (OBPs) are involved in the first step of the olfactory signal transduction pathway and the detection of host volatiles. However, the olfactory mechanism of OBPs in SHB-localized bee colonies is unclear. In this study, electroantennogram (EAG) and behavioral bioassay showed that only three compounds (2-heptanone, ocimene, and ethyl palmitate) from bee colonies triggered high electrophysiological and behavioral responses. Three antenna-specific OBP genes (OBP6, OBP11, and OBP19) were identified, and they were significantly expressed on adult days 6-7. Furthermore, by combining RNA interference (RNAi) with EAG, olfactometer bioassay, competitive fluorescence binding assays, and molecular docking, we found that these three OBP genes were involved in the recognition of 2-heptanone and ethyl palmitate, and AtumOBP6 is also involved in the recognition of ocimene. These data indicate that AtumOBP6, AtumOBP11, and AtumOBP19 play an important role in the olfactory response to bee colony volatiles. Our results provide new insights into the functions of the OBP families in A. tumida and help to explore more potential target genes for environmentally friendly pest control strategies.

The Female-Biased General Odorant Binding Protein 2 of Semiothisa cinerearia Displays Binding Affinity for Biologically Active Host Plant Volatiles

Herbivorous insects rely on volatile chemical cues from host plants to locate food sources and oviposition sites. General odorant binding proteins (GOBPs) are believed to be involved in the detection of host plant volatiles. In the present study, one GOBP gene, ScinGOBP2, was cloned from the antennae of adult Semiothisa cinerearia. Reverse-transcription PCR and real-time quantitative PCR analysis revealed that the expression of ScinGOBP2 was strongly biased towards the female antennae. Fluorescence-based competitive binding assays revealed that 8 of the 27 host plant volatiles, including geranyl acetone, decanal, cis-3-hexenyl n-valerate, cis-3-hexenyl butyrate, 1-nonene, dipentene, α-pinene and β-pinene, bound to ScinGOBP2 (KD = 2.21-14.94 μM). The electrical activities of all eight ScinGOBP2 ligands were confirmed using electroantennography. Furthermore, oviposition preference experiments showed that eight host volatiles, such as decanal, cis-3-hexenyl n-valerate, cis-3-hexenyl butyrate, and α-pinene, had an attractive effect on female S. cinerearia, whereas geranyl acetone, 1-nonene, β-pinene, and dipentene inhibited oviposition in females. Consequently, it can be postulated that ScinGOBP2 may be implicated in the perception of host plant volatiles and that ScinGOBP2 ligands represent significant semiochemicals mediating the interactions between plants and S. cinerearia. This insight could facilitate the development of a chemical ecology-based approach for the management of S. cinerearia.

Identifying the Key Role of Plutella xylostella General Odorant Binding Protein 2 in Perceiving a Larval Attractant, (E,E)-2,6-Farnesol

There is currently a lack of effective olfaction-based techniques to control diamondback moth (DBM) larvae. Identifying behaviorally active odorants for DBM larvae and exploring their recognition mechanisms can provide insights into olfaction-based larval control strategies. Through the two-choice assay, (E,E)-2,6-farnesol (farnesol) was identified as a compound exhibiting significant attractant activity toward DBM larvae, achieving an attraction index of 0.48 ± 0.13. PxylGOBP1 and PxylGOBP2, highly expressed in the antennae of DBM larvae, both showed high affinity toward farnesol. RNAi technology was used to knock down PxylGOBP1 and PxylGOBP2, revealing that the attraction of DBM larvae to farnesol nearly vanished following the knockdown of PxylGOBP2, indicating its critical role in recognizing farnesol. Further investigation into the PxylGOBP2-farnesol interaction revealed the importance of residues like Thr9, Trp37, and Phe118 in PxylGOBP2's binding to farnesol. This research is significant for unveiling the olfactory mechanisms of DBM larvae and developing larval behavior regulation techniques.

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.

Antennal transcriptome analysis of Psyttalia incisi (silvestri) (Hymenoptera: Braconidae): identification and tissue expression profiling of candidate odorant-binding protein genes

BACKGROUND

Olfaction plays an important role in host-seeking by parasitoids, as they can sense chemical signals using sensitive chemosensory systems. Psyttalia incisi (Silvestri) (Hymenoptera: Braconidae) is the dominant parasitoid of Bactrocera dorsalis (Hendel) in fruit-producing regions of southern China. The olfactory behavior of P. incisi has been extensively studied; however, the chemosensory mechanisms of this species are not fully understood.

RESULTS

Bioinformatics analysis of 64,515 unigenes from the antennal transcriptome of both male and female adults P. incisi identified 87 candidate chemosensory genes. These included 13 odorant-binding proteins (OBPs), seven gustatory receptors (GRs), 55 odorant receptors (ORs), 10 ionotropic receptors (IRs), and two sensory neuron membrane proteins (SNMPs). Phylogenetic trees were constructed to predict evolutionary relationships between these chemosensory genes in hymenopterans. Moreover, the tissue expression profiles of 13 OBPs were analyzed by quantitative real-time PCR, revealing high expression of seven OBPs (1, 3, 6, 7, 8, 12, and 13) in the antennae.

CONCLUSION

This study represents the first identification of chemosensory genes and the determination of their expression patterns in different tissues of P. incisi. These results contribute to a better understanding of the function of the chemosensory system of this parasitoid species.

Molecular and Functional Characterization of Three General Odorant-Binding Protein 2 Genes in Cydia pomonella (Lepidoptera: Tortricidae)

General odorant-binding proteins (GOBPs) play a crucial role in the detection of host plant volatiles and pheromones by lepidopterans. Previous studies identified two duplications in the GOBP2 gene in Cydia pomonella. In this study, we employed qRT-PCR, protein purification, and fluorescence competitive binding assays to investigate the functions of three GOBP2 genes in C. pomonella. Our findings reveal that CpomGOBP2a and CpomGOBP2b are specifically highly expressed in antennae, while CpomGOBP2c exhibits high specific expression in wings, suggesting a potential divergence in their functions. Recombinant proteins of CpomGOBP2a, CpomGOBP2b, and CpomGOBP2c were successfully expressed and purified, enabling an in-depth exploration of their functions. Competitive binding assays with 20 host plant volatiles and the sex pheromone (codlemone) demonstrated that CpomGOBP2a exhibits strong binding to four compounds, namely butyl octanoate, ethyl (2E,4Z)-deca-2,4-dienoate (pear ester), codlemone, and geranylacetone, with corresponding dissolution constants (Ki) of 8.59993 μM, 9.14704 μM, 22.66298 μM, and 22.86923 μM, respectively. CpomGOBP2b showed specific binding to pear ester (Ki = 17.37481 μM), while CpomGOBP2c did not exhibit binding to any tested compounds. In conclusion, our results indicate a functional divergence among CpomGOBP2a, CpomGOBP2b, and CpomGOBP2c. These findings contribute valuable insights for the development of novel prevention and control technologies and enhance our understanding of the evolutionary mechanisms of olfactory genes in C. pomonella.

Binding Properties of Odorant-Binding Protein 7 to Host Volatiles in Larvae of Spodoptera frugiperda

The chemosensory system is crucial during the growth and development of the moths. Spodoptera frugiperda (Lepidoptera: Noctuidae) is one of the most destructive insect pests. However, there is little functional research on odorant-binding proteins (OBPs) in the larval stage of S. frugiperda. Here, we obtained SfruOBP7 from transcriptomics and conducted the sequence analysis. We used quantitative real-time PCR to explore the expression profiles of SfruOBP7. The function identification showed that SfruOBP7 has a binding ability to 18 plant volatiles. Further molecular docking and site-directed mutant assay revealed that Lys45 and Phe110 were the key binding sites for SfruOBP7 interacting with linalool. In the behavior assays, linalool could attract the larvae, and dsOBP7-treated larvae lost their attraction to linalool. Our results help to reveal the essential molecular mechanism of the olfactory perception in the larvae and design an attractant based on the host volatiles.