Cloning, expression and immunocytochemical localization of a general odorant-binding protein gene from Helicoverpa armigera (Hübner)

Expression, affinity, and binding mode analysis of antennal-binding protein X in the variegated cutworm Peridroma saucia (Hübner)

The variegated cutworm Peridroma saucia (Hübner) is a worldwide pest that causes serious damage to many crops. Odorant-binding proteins (OBPs) are small soluble proteins involved in the first step of odorant reception. In moths, antennal-binding protein Xs (ABPXs) represent a main subfamily of classic OBPs. However, their functions remain unclear. Here, we cloned the ABPX gene from the antennae of P. saucia. RT-qPCR and western-blot analyses showed that PsauABPX is antenna-predominant and male-biased. Further temporal expression investigation indicated that the expression of PsauABPX started 1 day before eclosion and reached the highest 3 days after eclosion. Next, fluorescence binding assays revealed that recombinant PsauABPX had high binding affinities with P. saucia female sex pheromone components Z11-16: Ac and Z9-14: Ac. Then, molecular docking, molecular dynamics simulation, and site-directed mutagenesis were employed to identify key amino acid residues involved in the binding of PsauABPX to Z11-16: Ac and Z9-14: Ac. The results demonstrated that Val-32, Gln-107 and Tyr-114 are essential for the binding to both sex pheromones. This study not only give us insight into the function and binding mechanism of ABPXs in moths, but could also be used to explore novel strategies to control P. saucia.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Involvement of GOBP2 in the perception of a sex pheromone component in both larval and adult Spodoptera litura revealed using CRISPR/Cas9 mutagenesis

General odorant-binding proteins (GOBPs) are long considered responsible for the perception of plant odorants. In this study with the important noctuid pest Spodoptera litura, we functionally characterized that GOBP2 is also involved in the perception of sex pheromone components using in vivo CRISPR/Cas9 technique. First, the GOBP2 sgRNA and Cas9 protein were injected into the newly laid insect eggs, resulting in a 35.6% target mutagenesis in G0 moths. Then, the homozygous GOBP2 knockout strain (GOBP2^-/-) was obtained after the screening of three generations. The knockout male and female moths displayed a significant reduction in EAG responses to the sex pheromone components, and the knockout females also displayed a significant reduction to plant odorants. In the behavioral assay of food choice, GOBP2^-/- larvae lost the preference to artificial diet added with the major sex pheromone component Z9, E11-tetradecadienyl acetate (Z9, E11-14:Ac), whereas the WT larvae highly preferred the pheromone diet. Y-tube olfactometer assay and direct pheromone stimulation assay showed that GOBP2^-/- male adults reduced significantly than WT males in percentages of choice, hair pencil displaying and mating attempt to Z9, E11-14:Ac. In the oviposition test, GOBP2^-/- females showed significantly reduced preference for the soybean plants compared to the WT females. Our study demonstrated that GOBP2 plays an important role in perceiving sex pheromones in adult and larval stages, providing new insight into sex pheromone perception and a potential target for sex pheromone-based behavioral regulation in the pest.

An Expanded Survey of the Moth PBP/GOBP Clade in Bombyx mori: New Insight into Expression and Functional Roles

We studied the expression profile and ontogeny (from the egg stage through the larval stages and pupal stages, to the elderly adult age) of four OBPs from the silkworm moth Bombyx mori. We first showed that male responsiveness to female sex pheromone in the silkworm moth B. mori does not depend on age variation; whereas the expression of BmorPBP1, BmorPBP2, BmorGOBP1, and BmorGOBP2 varies with age. The expression profile analysis revealed that the studied OBPs are expressed in non-olfactory tissues at different developmental stages. In addition, we tested the effect of insecticide exposure on the expression of the four OBPs studied. Exposure to a toxic macrolide insecticide endectocide molecule (abamectin) led to the modulated expression of all four genes in different tissues. The higher expression of OBPs was detected in metabolic tissues, such as the thorax, gut, and fat body. All these data strongly suggest some alternative functions for these proteins other than olfaction. Finally, we carried out ligand docking studies and reported that PBP1 and GOBP2 have the capacity of binding vitamin K1 and multiple different vitamins.

Genetic knockout and general odorant-binding/chemosensory protein interactions: Revealing the function and importance of GOBP2 in the yellow peach moth's olfactory system

The GOBP2 protein has a unique function in the yellow peach moth (Conogethes punctiferalis (Guenée)). Several general odorant-binding proteins (GOBPs) have been identified in various lepidopteran species, but the functional difference between GOBP1 and GOBP2 in recognition of host plant odorants is still unknown. The functions of GOBP1 and GOBP2 in the yellow peach moth were evaluated in this study by using the CRISPR-Cas9 system. The results revealed the importance of GOBP2 in the olfaction mechanism in the yellow peach moth. The perception of the GOBP1-knockout larvae toward feeding decreased but did not reach a significant level while knocking out the GOBP2 and GOBP1/2 genes resulted in huge differences. On the other hand, electroantennograms (EAGs) and wind tunnel tests showed that the sensitivity of GOBP2 knockout adults to odorants decreased more than that of GOBP1 knockout individuals. The results of STRING database text mining grabbed our attention in protein-protein interaction studies. In this research, we first proved the existence of physical interactions between GOBPs and chemosensory proteins (CSPs) through the surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC) methods. Interestingly, GOBP1 and GOBP2 could not interact with each other, but they could interact with CSPs. The interaction results indicated that GOBP2 could physically interact with CSP15, CSP5, and OBP17, whereas GOBP1 could bind only with CSP5 and CSP10, and its association constant (k_a) was also more substantial than that of GOBP1. These results strongly suggest the importance of the function of GOBP2 in the perception of host plant odorants by the yellow peach moth.

Contribution of odorant binding proteins to olfactory detection of (Z)-11-hexadecenal in Helicoverpa armigera

Helicoverpa armigera utilizes (Z)-11-hexadecenal (Z11-16:Ald) as its major sex pheromone component. Three pheromone binding proteins (PBPs) and two general odorant binding proteins (GOBPs) are abundantly expressed in the male antennae of H. armigera. However, their precise roles in the olfactory detection of Z11-16:Ald remain enigmatic. To answer this question, we first synthesized the antibody against HarmOR13, an olfactory receptor (OR) primarily responding to Z11-16:Ald and mapped the local associations between PBPs/GOBPs and HarmOR13. Immunostaining showed that HarmPBPs and HarmGOBPs were localized in the supporting cells of trichoid sensilla and basiconic sensilla respectively. In particular, HarmPBP1 and HarmPBP2 were colocalized in the cells surrounding the olfactory receptor neurons (ORNs) expressing HarmOR13. Next, using two noninterfering binary expression tools, we heterologously expressed HarmPBP1, HarmPBP2 and HarmOR13 in Drosophila T1 sensilla to validate the functional interplay between PBPs and HarmOR13. We found that the addition of HarmPBP1 or HarmPBP2, not HarmPBP3, significantly increased HarmOR13's response to Z11-16:Ald. However, the presence of either HarmPBP1 or HarmPBP2 was ineffective to change the tuning breadth of HarmOR13 and modulate the response kinetics of this receptor. Taken together, this work demonstrates both HarmPBP1 and HarmPBP2 are involved in Z11-16:Ald detection. Our results support the idea that PBPs can contribute to the peripheral olfactory sensitivity but do little in modulating the selectivity and the response kinetics of corresponding ORs.

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.

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

BACKGROUND

The peach fruit moth, Carposina sasakii Matsumura (Lepidoptera: Carposinidae), is one of the most destructive pests of pome and stone fruits, while few studies of their molecular biology and physiology have been conducted. Research into CsasPBPs (Carposina sasakii pheromone binding proteins) and CsasGOBPs (Carposina sasakii general odorant binding proteins) may provide insights in to the mechanisms of olfaction in Carposina sasakii.

RESULTS

In our study, results of real time quantitative polymerase chain reaction (qPCR) assays demonstrated that CsasPBP1-3 and CsasGOBP1-2 transcripts were abundantly expressed in the antennae of both sexes, suggesting they play a vital role in olfaction. In addition, to examine specific functional differences between pheromone binding proteins (PBPs) and general odorant binding proteins (GOBPs), fluorescence competitive binding assays were used to measured the binding affinities for the two sex pheromones and 18 apple plant volatiles. As a result, both PBPs and GOBPs showed stronger binding affinities to Z-7-eicosene-11-one than Z-7-nonadecene-11-one in two sex pheromones, whereas only PBP3 exhibited specific affinity towards both these two sex pheromone components, and PBP1 showed a high binding affinity to the sex pheromone components, and to other plant volatiles. In addition, GOBP1-2 displayed high binding affinity to general components of plant volatiles.

CONCLUSION

Our study suggested CsasPBPs and CsasGOBPs play distinct physiological roles in the perception of sex pheromones and host plant volatiles. © 2018 Society of Chemical Industry.

Sensilla on six olfactory organs of male Eogystia hippophaecolus (Lepidoptera: Cossidae)

Eogystia hippophaecolus (Hua et al.) is an important boring pest that primarily damages sea buckthorn, causing large ecological and economic damages in China. In this study, we used scanning electron microscopy to investigate the sensilla on six olfactory tissues of male E. hippophaecolus: antennae, labial palps, external genitals, propodeum, mesopodium, and metapedes. On the antennae, two types of sensillum trichodea, two types of sensillum basiconica, a type of sensillum coeloconica, and Böhm's bristles were found. The labial palps had sensilla trichodea and chaetica. On the external genitals, three types of sensilla trichodea were the only sensilla. Böhm bristles were found on the base of the tibia and at the terminus of the tarsus. Most sensilla were distributed on the tarsus of the three pairs of legs, and notably, a majority of which were sensilla trichodea and sensilla chaetica, were on the pretarsus and telotarsus of the three pairs of legs. In this study, the distribution, number, type, and morphology of the sensilla on six olfactory organs of E. hippophaecolus were determined, which established the foundation for a future immunohistochemical search of olfactory proteins. RESEARCH HIGHLIGHTS: Eogystia hippophaecolus is a serious pest of seabuckthorn. The distribution, number, type, and morphology of olfactory sensilla of E. hippophaecolus are determined. The function and distribution of sensilla are compared with those of other insects.

The Odorant Binding Protein 6 Expressed in Sensilla Chaetica Displays Preferential Binding Affinity to Host Plants Volatiles in Ectropis obliqua

The monophagous tea geometrid Ectropis obliqua selectively feed on tea plants, requiring the specialized chemosensory system to forage for certain host. A deep insight into the molecular basis would accelerate the design of insect-behavior-modifying stimuli. In the present study, we focused on the odorant-binding protein 6 (EoblOBP6) with the high abundance in legs transcriptome of E. obliqua moths. qRT-PCR coupled with western blot analyses revealed the dual expression pattern of EoblOBP6 in antennae and legs. Cellular immunolocalization indicated that EoblOBP6 was predominantly labeled in the outer sensillum lymph of uniporous sensilla chaetica, which is not innervated by sensory neurons. No specific staining was observed in other sensillum types. The fluorescence competition assay showed a relatively narrow binding spectrum of recombinant EoblOBP6. EoblOBP6 could not only bind with intact tea plant volatiles benzaldehyde but also display high binding ability to nerolidol and α-farnesene which are tea plant volatiles dramatically induced by herbivore infestation. Besides, EoblOBP6 tightly bound to the aversive bitter alkaloid berberine. Taken together, EoblOBP6 displayed an unusual expression in sensilla chaetica, exhibited the potential involvement in olfaction and gustation, and may play a functional role in host location of female E. obliqua moths.

Functional Characteristics, Electrophysiological and Antennal Immunolocalization of General Odorant-Binding Protein 2 in Tea Geometrid, Ectropis obliqua

As one of the main lepidopteran pests in Chinese tea plantations, Ectropisobliqua Warren (tea geometrids) can severely decrease yields of tea products. The olfactory system of the adult tea geometrid plays a significant role in seeking behaviors, influencing their search for food, mating partners, and even spawning grounds. In this study, a general odorant-binding protein (OBP) gene, EoblGOBP2, was identified in the antennae of E. obliqua using reverse transcription quantification PCR (RT-qPCR). Results showed that EoblGOBP2 was more highly expressed in the antennae of males than in females relative to other tissues. The recombinant EoblGOBP2 protein was prepared in Escherichia coli and then purified through affinity chromatography. Ligand-binding assays showed that EoblGOBP2 had a strong binding affinity for some carbonyl-containing tea leaf volatiles (e.g., (E)-2-hexenal, methyl salicylate, and acetophenone). Electrophysiological tests confirmed that the male moths were more sensitive to these candidate tea plant volatiles than the female moths. Immunolocalization results indicated that EoblGOBP2 was regionally confined to the sensilla trichoid type-II in the male antennae. These results indicate that EoblGOBP2 may be primarily involved in the olfactory activity of male E. obliqua moths, influencing their ability to sense tea leaf volatiles. This study provides a new perspective of insect GOBPs and implies that olfactory function can be used to prevent and control the tea geometrid.

Transcriptome analysis in different developmental stages of Batocera horsfieldi (Coleoptera: Cerambycidae) and comparison of candidate olfactory genes

The white-striped longhorn beetle Batocera horsfieldi (Coleoptera: Cerambycidae) is a polyphagous wood-boring pest that causes substantial damage to the lumber industry. Moreover olfactory proteins are crucial components to function in related processes, but the B. horsfieldi genome is not readily available for olfactory proteins analysis. In the present study, developmental transcriptomes of larvae from the first instar to the prepupal stage, pupae, and adults (females and males) from emergence to mating were built by RNA sequencing to establish a genetic background that may help understand olfactory genes. Approximately 199 million clean reads were obtained and assembled into 171,664 transcripts, which were classified into 23,380, 26,511, 22,393, 30,270, and 87, 732 unigenes for larvae, pupae, females, males, and combined datasets, respectively. The unigenes were annotated against NCBI’s non-redundant nucleotide and protein sequences, Swiss-Prot, Gene Ontology (GO), Pfam, Clusters of Eukaryotic Orthologous Groups (KOG), and KEGG Orthology (KO) databases. A total of 43,197 unigenes were annotated into 55 sub-categories under the three main GO categories; 25,237 unigenes were classified into 26 functional KOG categories, and 25,814 unigenes were classified into five functional KEGG Pathway categories. RSEM software identified 2,983, 3,097, 870, 2,437, 5,161, and 2,882 genes that were differentially expressed between larvae and males, larvae and pupae, larvae and females, males and females, males and pupae, and females and pupae, respectively. Among them, genes encoding seven candidate odorant binding proteins (OBPs) and three chemosensory proteins (CSPs) were identified. RT-PCR and RT-qPCR analyses showed that BhorOBP3, BhorCSP2, and BhorOBPC1/C3/C4 were highly expressed in the antenna of males, indicating these genes may may play key roles in foraging and host-orientation in B. horsfieldi. Our results provide valuable molecular information about the olfactory system in B. horsfieldi and will help guide future functional studies on olfactory genes.

Sex pheromone recognition and characterization of three pheromone-binding proteins in the legume pod borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae)

Pheromone-binding proteins (PBPs) are essential for the filtering, binding and transporting of sex pheromones across sensillum lymph to membrane-associated pheromone receptors of moths. In this study, three novel PBP genes were expressed in Escherichia coli to examine their involvement in the sex pheromone perception of Maruca vitrata. Fluorescence binding experiments indicated that MvitPBP1-3 had strong binding affinities with four sex pheromones. Moreover, molecular docking results demonstrated that six amino acid residues of three MvitPBPs were involved in the binding of the sex pheromones. These results suggested that MvitPBP1-3 might play critical roles in the perception of female sex pheromones. Additionally, the binding capacity of MvitPBP3 with the host-plant floral volatiles was high and was similar to that of MvitGOBP2. Furthermore, sequence alignment and docking analysis showed that both MvitGOBP2 and MvitPBP3 possessed an identical key binding site (arginine, R130/R140) and a similar protein pocket structure around the binding cavity. Therefore, we hypothesized that MvitPBP3 and MvitGOBP2 might have synergistic roles in binding different volatile ligands. In combination, the use of synthetic sex pheromones and floral volatiles from host-plant may be used in the exploration for more efficient monitoring and integrated management strategies for the legume pod borer in the field.

Identification and characterisation of two general odourant-binding proteins from the litchi fruit borer, Conopomorpha sinensis Bradley

BACKGROUND

The litchi fruit borer, Conopomorpha sinensis Bradley, is one of the most destructive pests of litchi and longan fruits in south-east Asia and southern China, yet the molecular biology and physiology of this pest remain poorly understood. Control of this insect pest may be achieved by interfering with its recognition of host plants.

RESULTS

In this study, two cDNAs encoding CsGOBP1 and CsGOBP2 were identified from the antennae of C. sinensis, and a comparative study on these two C. sinensis GOBPs (CsGOBPs) was conducted. The secondary structure of these two CsGOBPs mainly consists of six α-helices, but three-dimensional structural predictions of CsGOBP1 and CsGOBP2 indicated significant difference in the final 3D models. Results in real-time PCR assays indicated that the two CsGOBPs had different tissue- and sex-dependent expression patterns. A competitive binding assay revealed that CsGOBP1 considerably prefer the component exhibited in Guiwei or Feizixiao litchi cultivar, while CsGOBP2 bind to general volatile components from nine litchi cultivars. Additionally, ethyl acetate has higher binding affinities to CsGOBP2 protein than to CsGOBP1, and has remarkable attraction to female C. sinensis moths in Y-tube olfactometer assays.

CONCLUSION

These results strongly suggest functional difference between these two CsGOBPs in perception of host plant odourants.

Venom of the parasitoid wasp Pteromalus puparum contains an odorant binding protein

Odorant binding proteins (OBPs) are crucial for insects to detect food, mates, predators, or other purposes. They are mostly located on antennae and other olfactory sensilla. In this study, we identified an OBP from the venom of Pteromalus puparum, designated as PpOBP. The cDNA of PpOBP is 517 bp in length, encoding 132 amino acids. Phylogenetic analysis revealed that PpOBP was clustered with OBP68 and OBP67 of Nasonia vitripennis. PpOBP was highly expressed in the venom apparatus at the transcriptional and translational levels. PpOBP was located in all parts of venom apparatus including venom gland, venom reservoir, and Dufour's gland. During 0-6 days post adult eclosion, the PpOBP mRNA level peaked at 2 days in the venom apparatus, whereas the protein remained at a high level. In the venom apparatus, the PpOBP mRNA was significantly upregulated following feeding with honey and parasitization. We propose that PpOBP is involved in parasitoid-host interactions.

Pheromone reception in moths: from molecules to behaviors

Male moths detect and find their mates using species-specific sex pheromones emitted by conspecific females. Olfaction plays a vital role in this behavior. Since the first discovery of an insect sex pheromone from the silkmoth Bombyx mori, great efforts have been spent on understanding the sensing of the pheromones in vivo. Much progress has been made in elucidating the molecular mechanisms that mediate chemoreception in insects in the past few decades. In this review, we focus on pheromone reception and detection in moths, from the molecular to the behavioral level. We trace the information pathway from the capture of pheromone by male antennae, binding and transportation to olfactory receptor neurons, receptor activation, signal transduction, molecule inactivation, through brain processing and behavioral response. We highlight the impact of recent studies and also provide our insights into pheromone processing.

Processing of Pheromone Information in Related Species of Heliothine Moths

In heliothine moths, the male-specific olfactory system is activated by a few odor molecules, each of which is associated with an easily identifiable glomerulus in the primary olfactory center of the brain. This arrangement is linked to two well-defined behavioral responses, one ensuring attraction and mating behavior by carrying information about pheromones released by conspecific females and the other inhibition of attraction via signal information emitted from heterospecifics. The chance of comparing the characteristic properties of pheromone receptor proteins, male-specific sensory neurons and macroglomerular complex (MGC)-units in closely-related species is especially intriguing. Here, we review studies on the male-specific olfactory system of heliothine moths with particular emphasis on five closely related species, i.e., Heliothis virescens, Heliothis subflexa, Helicoverpa zea, Helicoverpa assulta and Helicoverpa armigera.

Expression patterns and binding properties of three pheromone binding proteins in the diamondback moth, Plutella xyllotella

Pheromone binding proteins (PBPs) play a key role in transporting hydrophobic sex pheromone components emitted by con-specific female across aqueous sensillar lymph to the surface of olfactory receptor neurons. A number of PBPs have been cloned, however, details of their function are still largely unknown. Here three pheromone binding protein genes in the diamondback moth, Plutella xyllotella were cloned. The three PxylPBP genes are not only expressed in chemosensory tissues but also expressed in female reproductive organs and male legs. To better understand the functions of PxylPBPs in the initial steps of pheromone recognition, three PxylPBPs were expressed in Escherichia coli and the ligand-binding specificities of purified recombinant PBPs were investigated. Fluorescence binding assays indicate that three PxylPBPs not only robustly bound all four sex pheromone components but also significantly bound pheromone analogs with at least one double bond, while weakly bound tested plant volatiles. Although pheromone analogs bound PBPs, they could not elicit the moth's electrophysiological response. These experiments provide evidence that PxylPBPs have limited selectivity of pheromone components and analogs and some downstream components such as odor receptors might be involved in selectivity and specificity of pheromone perception in P. xyllotella.

Characterization of three pheromone-binding proteins (PBPs) of Helicoverpa armigera (Hübner) and their binding properties

Three pheromone-binding proteins of Helicoverpa armigera were cloned and expressed in Escherichia coli. In order to characterize their physiological properties, ligand-binding experiments were performed using five biologically relevant substances including sex pheromones and interspecific signals. The results showed that one of the pheromone-binding proteins, HarmPBP1, binds strongly to each of the two principal pheromone components of H. armigera, (Z)-11-tetradecenal and (Z)-9-hexadecenal, but not to the interspecific signal (Z)-9-tetracecenal. The two remaining pheromone-binding proteins, HarmPBP2 and HarmPBP3, showed only weak affinities with the ligands tested. The 3-D structure of HarmPBP1 was predicted and the docking experiments indicate that the key binding site of (Z)-9-hexadecenal to HarmPBP1 includes Thr112, Lys111, and Phe119 whereas that of (Z)-11-tetradecenal includes Ser9, Trp37, Phe36, and Phe119.

Identification and characterization of two general odorant binding protein genes from the oriental fruit moth, Grapholita molesta (busck)

Two novel general odorant-binding protein (GOBP) cDNAs (GmolGOBP1 and GmolGOBP2) were cloned and characterized from female antennal tissue of the oriental fruit moth, Grapholita molesta. We focused our investigation on this olfactory protein family by using reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends-PCR (RACE-PCR). The full-length open reading frames of GmolGOBP1 and GmolGOBP2 were 492 and 483 nucleotides long, which encode 164 and 161 amino acid residue peptides, respectively. Protein signature analyses revealed that they each contained six conserved cysteines with an N-terminal signal sequence of 20 amino acids. The alignment of the two deduced protein sequences with other Lepidoptera GOBPs showed high sequence similarity (70-80%) with other full-length sequences from GenBank. Sequence similarity between the two GOBPs was only 48%, suggesting that the two proteins belong to different classes of lepidopteran GOBPs. RT-PCR analysis revealed that the two GOBP genes were expressed only in antennae of both sexes. Real-time PCR analysis further indicated that the transcript level of GmolGOBP1 was higher in males than in females, whereas the transcript level of GmolGOBP2 was higher in females than in males. Temporally, the two GOBP genes were expressed during the complete photoperiod (15L:9D). The highest transcript levels of GmolGOBP1 in both sexes and GmolGOBP2 in females were detected at the end of photophase and during scotophase. The expression of GmolGOBP2 in males remained at similar levels during the complete photoperiod. Based on these results, the possible physiological functions of GmolGOBPs are discussed.

Mimicking nature's noses: from receptor deorphaning to olfactory biosensing

The way in which organisms detect specific volatile compounds within their environment, and the associated neural processing which produces perception and subsequent behavioural responses, have been of interest to scientists for decades. Initially, most olfaction research was conducted using electrophysiological techniques on whole animals. However, the discovery of genes encoding the family of human olfactory receptors (ORs) paved the way for the development of a range of cellular assays, primarily used to deorphan ORs from mammals and insects. These assays have greatly advanced our knowledge of the molecular basis of olfaction, however, while there is currently good agreement on vertebrate and nematode olfactory signalling cascades, debate still surrounds the signalling mechanisms in insects. The inherent specificity and sensitivity of ORs makes them prime candidates as biological detectors of volatile ligands within biosensor devices, which have many potential applications. In the previous decade, researchers have investigated various technologies for transducing OR:ligand interactions into a readable format and thereby produce an olfactory biosensor (or bioelectronic nose) that maintains the discriminating power of the ORs in vivo. Here we review and compare the molecular mechanisms of olfaction in vertebrates and invertebrates, and also summarise the assay technologies utilising sub-tissue level sensing elements (cells and cell extracts), which have been applied to OR deorphanization and biosensor research. Although there are currently no commercial, "field-ready" olfactory biosensors of the kind discussed here, there have been several technological proof-of-concept studies suggesting that we will see their emergence within the next decade.

Cloning and eukaryotic expression of olfaction-related Gqα-protein gene in English grain aphid (Sitobion avenae)

Based on conserved homologous amino-acid sequences of the Gq protein α subunit in arthropods, a pair of degenerate primers were designed to amplify the gene from the English grain aphid (Sitobion avenae), using reverse transcriptase polymerase chain reaction (RT-PCR) and (3′/5′)-rapid amplification of cDNA ends (3′/5′ RACE) techniques. A Gqα protein was obtained from the alate adult aphids. The open reading-frame was 1062 bp, encoding 352 amino-acid residues with a calculated molecular weight of 40.8 kDa. The cDNA sequence was deposited in GenBank with accession no. EF638906. The deduced amino-acid sequence of Gqα shared a high identity (≥82.17%) with reported Gqα from other insects and even vertebrates, and had the typical characteristics of Gqα protein. In order to explore the function of the Gqα gene, a eukaryotic expressional system (baculovirus expression vector system, BEVS) was constructed by TOPO and Gateway techniques. After the recombinant reaction occurring between pUC-Gqα and the Gateway-adapted baculovirus DNA from Autographa californica nuclear polyhedrosis virus (AcMNPV), the construct recombinant viruses containing V5-His6Gqα were transfected singly into the insect cell line of Tn-5B1-4. After collecting the infected cell, detection was conducted by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting. The result showed that the system comprising recombinant baculovirus and Tn could express Gqα protein successfully.

Mutation of an aminopeptidase N gene is associated with Helicoverpa armigera resistance to Bacillus thuringiensis Cry1Ac toxin

A Cry1Ac-resistant strain (Bt-R) of Helicoverpa armigera, with 2971-fold resistance, was derived by selection with Cry1Ac toxin for 75 generations. We used cDNA-amplified fragment length polymorphism analysis to identify those genes differentially expressed in the Cry1Ac-resistant and -susceptible strains, which revealed 212 differentially expressed transcripts among 2000 screened cDNAs. Among these transcript-derived fragments (TDFs), 37 showed some homology to known sequences, including Aminopeptidase N (APN), which is expressed in the midgut epithelium and has been implicated as a Cry1A subfamily receptor in several moths, including H. armigera. We confirmed the TDF by RT-PCR and identified a deletion mutation of apn1 in the Bt-R strain. We expressed the TDF in bacteria. The partial HaAPN1-96S wild-type protein, bound to Cry1Ac on ligand blots, whereas HaAPN1-BtR did not. This suggested that HaAPN1 is a receptor for Bt Cry1Ac and that its deletion mutation is associated with Cry1Ac resistance in H. armigera. The absence of one binding site is responsible for its resistance to Cry1Ac. We developed an allele-specific PCR to monitor whether the apn1 gene in an H. armigera field population produced a similar mutation. No deleted mutants were found in 2250 individuals collected from the field in 2006-2007.

Cloning, expression and functional analysis of a general odorant-binding protein 2 gene of the rice striped stem borer, Chilo suppressalis (Walker) (Lepidoptera: Pyralidae)

A full-length cDNA encoding a general odorant binding protein 2 (GOBP2) was cloned from the antennae of the rice striped stem borer, Chilo suppressalis (Lepidoptera: Pyralidae), by the combination of reverse transcription PCR (RT-PCR) and rapid amplification of cDNA ends PCR (RACE-PCR). The cDNA contains a 489 bp open reading frame, which encodes a 162 amino acid protein, termed as Ch. suppressalis GOBP2 (CsupGOBP2). CsupGOBP2 is similar in the number of amino acids and protein sequence to GOBP2s in other species of Lepidoptera. RT-PCR results showed that CsupGOBP2 mRNA was highly expressed in the adult antennae of both females and males, as was CsupGOBP2 protein as revealed by Western blot analysis. CsupGOBP2 expressed in Escherichia coli was purified by affinity chromatography, refolding and gel filtration from the inclusion body. Fluorescence emission spectra and competitive binding assays by using N-phenyl-1-naphthylamine as first binding ligand and odorants as potential competitors revealed that the CsupGOBP2 protein has significant affinity to cis-11-hexadecenal (Z11-16:Ald), the main component of Ch. suppressalis pheromone and to laurinaldehyd and benzaldehyde, two general plant volatile aldehydes.

Molecular cloning and bacterial expression of pheromone binding protein in the antennae of Helicoverpa armigera (Hübner)

A cDNA clone coding for pheromone binding protein was isolated from the antennae of Helicoverpa armigera by RT-PCR and (5'/3')-RACE technique. The full-length of H. armigera pheromone binding protein (HarmPBP) was 952 bp, possessing 162 amino acid residues including a signal peptide of 20 amino acids. Its predicted molecular weight and isoelectric point were 18.26 kDa and 5.23, respectively. This deduced amino acid sequence shared some common structural features with odorant-binding proteins from several moth species, including the six conserved cysteine motif, a typical characteristic of insect's odorant-binding proteins. Northern blot showed that HarmPBP is specifically expressed in the antennae of Helicoverpa armigera and more abundantly expressed in male than female. During the antennal development, HarmPBP is first expressed about 4 days prior to adult eclosion and rises to a plateau 2 days prior to adult eclosion. In order to obtain sufficient PBP for further determining its biochemical and physiological properties, a bacterical expression vector of PBP was constructed and successfully expressed in Escherichia coli. The recombinant PBP was shown to cross-react with an anti-PBP antiserum from Antheraea polyphemus. Polyclonal antibodies against HarmPBP were used to mark the distribution of the protein in olfactory sensilla. Very strong labeling was observed in the sensillum lymph of the hair lumen and of the sensillum-lymph cavity. In the male, HarmPBP is expressed in sensilla trichodea and not in sensilla basiconica, while in the female, it is expressed both in sensilla basiconica and sensilla trichodea.