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

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.

The Odorant-Binding Protein 1 Mediates the Foraging Behavior of Grapholita molesta Larvae

Since eggs are laid directly on fruit skin, it is typically believed that food odor has little impact on the foraging of Grapholita molesta larvae. It is crucial to note that larvae that hatch on twigs and leaves could need some sort of identification system when foraging. Here, 22 GmolOBP genes were identified from the G. molesta larval transcriptome via the comparison of conserved domain and homology in the protein level. GmolOBP1 had strong affinities for important pear-fruit volatiles, which caused larvae strong behavioral responses. However, after GmolOBP1 silencing, the larvae lost their attraction to methyl salicylate, α-farnesene, butyl acetate, ethyl butanoate, and ethyl hexanoate, and the effects of larvae seeking various pears were significantly reduced. Consequently, GmolOBP1 was required for the reception of pear volatiles and was involved in mediating how G. molesta larvae foraged. Our research revealed the GmolOBP1 foraging signal recognition mechanism as well as potential molecular targets for field pest management.

Function of Cytochrome P450s and Gut Microbiome in Biopesticide Adaptation of Grapholita molesta on Different Host Diets

Insects that feed on various host plants possess diverse xenobiotic adaptations; however, the underlying mechanisms are poorly understood. In the present study, we used Grapholita molesta, which shifts feeding sites from peach shoots to apple fruits, as a model to explore the effects of shifts in host plant diet on the profiles of cytochrome P450s and the gut bacteria microbiome, as well as their effects on biopesticide adaptation. We found that the sensitivity of the fruit-feeding G. molesta to emamectin benzoate biopesticide was significantly lower than that of the shoot-feeding larvae. We also found that the P450 enzyme activity and the expression of nine cytochrome P450s were enhanced in G. molesta fed on Fuji apples compared to those fed on peach shoots. The survival rates of G. molesta exposed to emamectin benzoate significantly decreased as each of three of four emamectin benzoate-inducted cytochrome P450 genes were silenced. Furthermore, we discovered the gut bacteria dynamics of G. molesta changed with the host shift and the structure of the gut bacteria microbiome was determined by the final diet ingested; additionally, the dysbiosis of the gut microbiota induced by antibiotics could significantly increase the sensitivity to emamectin benzoate. Taken together, our results suggest that the expression of P450s and the composition of the gut bacteria microbiome promote adaptation to emamectin benzoate in G. molesta, providing new insights into the molecular mechanisms underlying xenobiotic adaptation in this notorious pest.

Molecular identification of carboxylesterase genes and their potential roles in the insecticides susceptibility of Grapholita molesta

Grapholita molesta is one of the most damaging pests worldwide in stone and pome fruits. Application of chemical pesticides is still the main method to control this pest, which results in resistance to several types of insecticides. Carboxylesterase (CarE) is one of the important enzymes involved in the detoxification metabolism and tolerance of xenobiotics and insecticides. However, the roles of CarEs in insecticides susceptibility of G. molesta are still unclear. In the present study, the enzyme activity of CarEs and the mRNA expression of six CarE genes were consistently elevated after treatment with three insecticides (emamectin benzoate, lambda-cyhalothrin, and chlorantraniliprole). According to spatio-temporal expression profiles, six CarE genes expressed differently in different developmental stages, and highly expressed in some detoxification metabolic organs. RNAi-mediated knockdown of these six CarE genes indicated that the susceptibility of G. molesta to all these three insecticides were obviously raised after GmCarE9, GmCarE14, GmCarE16, and GmCarE22 knockdown, respectively. Overall, these results demonstrated that GmCarE9, GmCarE14, GmCarE16, and GmCarE22 play a role in the susceptibility of G. molesta to emamectin benzoate, lambda-cyhalothrin, and chlorantraniliprole treatment. This study expands our understanding of CarEs in insects, that the same CarE gene could participate in the susceptibility to different insecticides.

Expression and functional analysis of an odorant binding protein PopeOBP16 from Phthorimaea operculella (Zeller)

Odorant binding proteins (OBPs) are essential proteins in the peripheral olfactory system, responsible for odorant recognition and transport to olfactory receptors. Phthorimaea operculella (potato tuber moth) is an important oligophagous pest on Solanaceae crops in many countries and regions. PopeOBP16 is one of the OBPs in potato tuber moth. This study examined the expression profiles of PopeOBP16. The results of qPCR indicated that PopeOBP16 was highly expressed in the antennae of adults, especially in males, suggesting that it may be involved in odor recognition in adults. The electroantennogram (EAG) was used to screen candidate compounds with the antennae of P. operculella. The relative affinities of PopeOBP16 to 27 host volatiles and two sex pheromone components with the highest relative EAG responses were examined with competitive fluorescence-based binding assays. PopeOBP16 had the strongest binding affinity with the plant volatiles: nerol, 2-phenylethanol, linalool, 1,8-cineole, benzaldehyde, β-pinene, d-limonene, terpinolene, α-terpinene, and the sex pheromone component trans-4, cis-7, cis-10-tridecatrien-1-ol acetate. The results provide a foundation for further research into the functioning of the olfactory system and the potential development of green chemistry for control of the potato tuber moth.

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.

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

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

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

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

Identification and comparative expression analysis of odorant-binding proteins in the reproductive system and antennae of Athetis dissimilis

Odorant-binding proteins (OBPs) are prevalent in the antennal transcriptomes of different orders of insects. Studies on OBPs have focused on their role in the insect chemosensory system, but knowledge of their functions in the insect testis is limited. We sequenced the transcriptomes of the Athetis dissimilis reproductive organs and analyzed the expression of AdisOBP genes in different tissues. We identified 23 OBPs in the testis and ovaries and 31 OBPs in antennal transcriptomes. The results of real-time quantitative PCR revealed that 23 of the 54 OBP genes were highly expressed in both female and male antennae, including three that exhibited male-biased expression and 15 that exhibited female-biased expression. A total of 24 OBPs were highly expressed in the testis of A. dissimilis, while expression of OBPs in the ovaries was very low. These findings highlight the functional diversity of OBPs in insects and can facilitate further studies on the OBPs in A. dissimilis and lepidopteran species.

Glutaredoxins and thioredoxin peroxidase involved in defense of emamectin benzoate induced oxidative stress in Grapholita molesta

Glutaredoxins (Grxs) and thioredoxin peroxidases (Tpxs) are major antioxidant enzyme families involved in regulating cellular redox homeostasis and in defense of enhanced oxidative stress through scavenging reactive oxygen species (ROS). However, the functions of these enzymes have not been reported in the oriental fruit moth, Grapholita molesta (Busck), a worldwide pest of stone and pome fruits. Here, we identified four new antioxidant genes, GmGrx, GmGrx3, GmGrx5, and GmTpx which were induced by exposure with emamectin benzoate, a commonly used biopesticide for G. molesta control. Other environmental factors (low and high temperatures, Escherichia coli and Metarhizium anisopliae) also significantly induced the expression of these genes. After GmGrx or GmTpx silenced by RNA interference (RNAi), the percentage of larval survival to emamectin benzoate were significantly decreased, demonstrating that GmGrx and GmTpx are involved in protecting G. molesta from stresses induced by emamectin benzoate. Furthermore, silenced GmGrx, GmGrx3, GmGrx5, or GmTpx significantly enhanced the enzymatic activities of superoxide dismutase (SOD) (except GmTpx) and peroxidase (POD), as well as the contents of hydrogen peroxide and metabolites ascorbate. Taken together, our results suggest that GmGrx, GmGrx3, GmGrx5, and GmTpx may play critical roles in antioxidant defense. Specially, GmGrx and GmTpx contribute to the defense of oxidative damage induced by exposure to emamectin benzoate through scavenging excessive ROS in G. molesta. Our findings provided a theoretical basis for understanding functions of insect glutaredoxin and peroxidase systems.

Detecting Host-Plant Volatiles with Odorant Receptors from Grapholita molesta (Busck) (Lepidoptera: Tortricidae)

Grapholita molesta is a global pest of stone and pome fruits. The sensitive olfactory system plays a crucial role in regulating key behavioral activities of insects and G. molesta relies heavily on general odorant receptors (ORs) to detect host-plant volatiles. In this study, three general OR genes from G. molesta (GmolOR12, GmolOR20, and GmolOR21) were identified. Quantitative polymerase chain reaction revealed that GmolORs expression was considerably higher in adults and adult antennae than in any other life stages and body parts, respectively. Moreover, the expression of GmolORs was significantly higher in the antennae of females than in those of males, with a peak in the antennae of 3-days-old adult females. GmolOR20 and GmolOR21 displayed no responses to any of the odorant compounds tested in the Xenopus oocyte system. GmolOR12 was tuned mainly to 5 of the 47 odorant components tested (including decanol, heptanal, octanal, nonanal, and decanal), and the response to aldehydes among the 5 components was the highest. Additionally, they all elicited female and male antennae electroantennogram responses, and the aldehydes elicited the highest response among the 5 components. These results suggested that GmolOR12 in the G. molesta olfactory system plays an important role in sensing aldehydes and that GmolOR12 is involved in sensing host-plant volatiles. These findings provide insight into the possibility of using host-plant volatiles for the control of G. molesta.

Molecular and Functional Characterization of Odorant Binding Protein 7 From the Oriental Fruit Moth Grapholita molesta (Busck) (Lepidoptera: Tortricidae)

Odorant-binding proteins (OBPs) are widely and abundantly distributed in the insect sensillar lymph and are essential for insect olfactory processes. The OBPs can capture and transfer odor molecules across the sensillum lymph to odorant receptors and trigger the signal transduction pathway. In this study, a putative OBP gene, GmolOBP7, was cloned using specific-primers, based on the annotated unigene which forms the antennal transcriptome of Grapholita molesta. Real-time PCR (qRT-PCR) analysis revealed that GmolOBP7 was highly expressed in the wings of males and the antennae of both male and female adult moths, while low levels were expressed in other tissues. The recombinant GmolOBP7 (rGmolOBP7) was successfully expressed and purified via Ni-ion affinity chromatography. The results of binding assays revealed that rGmolOBP7 exhibited a high binding affinity to the minor sex pheromone 1-dodecanol containing K_i of 7.48 μM and had high binding capacities to the host-plant volatiles, such as pear ester, lauraldehyde and α-ocimene. RNA-interference experiments were performed to further assess the function of GmolOBP7. qRT-PCR showed that the levels of mRNA transcripts significantly declined in 1 and 2 day old male and female moths, treated with GmolOBP7 dsRNA, compared with non-injection controls. The EAG responses of dsRNA-injected males and females to pear ester, as well as the EAG responses of dsRNA-injected males to 1-dodecanol, were significantly reduced compared to the GFP-dsRNA-injected and non-injected controls. We therefore infer that GmolOBP7 has a dual function in the perception and recognition of the host-plant volatiles and sex pheromones.

Degradation of sex pheromone and plant volatile components by an antennal glutathione S-transferase in the oriental fruit moth,Grapholita molesta Busck (Lepidoptera: Tortricidae)

Insect antennae have a primary function of perceiving and discerning odorant molecules including sex pheromones and host plant volatiles. The assumption that genes highly expressed in the antennae may have an olfactory-related role associated with signal transduction. Here, one delta subfamily glutathione S-transferase (GST) gene (GmolGSTD1) was obtained from an antennal transcriptome of Grapholita molesta. Quantitative real-time polymerase chain reaction results revealed that GmolGSTD1 was mainly expressed in antennae and the expression levels were significantly higher in female antennae than in male antennae. The recombinant GmolGSTD1 (rGmolGSTD1) showed glutathione-conjugating activity toward 1-chloro-2,4-dinitrobenzene (CDNB) as substrates. The pH range for optimal rGmolGSTD1 enzyme activity was 6.0-6.5, and rGmolGSTD1 enzyme activity had maximal peaks at 35-40°C. Spectrophotometric analysis indicated that insecticides had weak inhibitory effects on the activity of rGmolGSTD1 with the inhibitory rates of 28.82% for chlorpyrifos, 22.27% for lambda-cyhalothrin, 18.07% for bifenthrin, 20.42% for acetamiprid, 17.57% for thiamethoxam, 25.67% for metaflumizone, 27.43% for abamectin, and 7.24% for chlorbenzuron. rGmolGSTD1 exhibited high degradation activity to the sex pheromone component (Z)-8-dodecenyl alcohol and the host plant volatile butyl hexanoate with the degradation efficiency of 75.01% and 48.54%, respectively. We speculate that GmolGSTD1 works in inactivating odorant molecules and maintaining sensitivity to olfactory communication of G. molesta.

Molecular and Functional Characterization of pheromone binding protein 1 from the Oriental Fruit Moth, Grapholita molesta (Busck)

Pheromone binding protein (PBP) is thought primarily to bind and transport the sex pheromone in moths. The accumulated studies suggest that three PBPs were identified in moth species. In Grapholita molesta, the functions of GmolPBP2 and GmolPBP3 have been previously studied. However, the function of GmolPBP1 is still unclear. Furthermore, the Cydia pomonella sex pheromone Codlemone can act as a sex pheromone synergist of G. molesta. In C. pomonella, CpomPBP1 specifically bind the Codlemone. CpomPBP1 displays high identity with GmolPBP1 (70%), indicating that the two PBPs may share a similar 3D structure thus can bind the similar or same ligands. In this study, we explored the molecular and functional characterization of GmolPBP1. GmolPBP1, bearing the typical characteristics of Lepidopteran odorant binding proteins, was closest phylogenetically to CpomPBP1. Binding studies demonstrated that GmolPBP1 exhibited strong binding affinities with (Z)-8-dodecenyl alcohol, 1-dodecanol and Codlemone. Molecular docking showed that GmolPBP1 has different ligand recognition mechanism for the three ligands. Our results suggest that GmolPBP1 functions as recognizer of (Z)-8-dodecenyl alcohol and 1-dodecanol of the female sex pheromone blend, and may be the potential transporter of Codlemone, which contributes to the synergism of the pheromone response of G. molesta by Codlemone.

Transcriptome Analysis and Identification of Major Detoxification Gene Families and Insecticide Targets in Grapholita Molesta (Busck) (Lepidoptera: Tortricidae)

The oriental fruit moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae), is an important pest of most stone and pome fruits and causes serious damage to the fruit industry worldwide. This insect pest has been primarily controlled through the application of insecticides; as a result, G. molesta has developed resistance to many different types of insecticides. To identify detoxification genes, we have, de novo, sequenced the transcriptome of G. molesta (Lepidoptera: Tortricidae) and yielded 58,970 unigenes of which 26,985 unigenes matched to known proteins. In total, 2,040 simple sequence repeats have been identified. The comprehensive transcriptome data set has permitted us to identify members of important gene families related to detoxification in G. molesta, including 77 unigenes of putative cytochrome P450s, 28 of glutathione S-transferases, 46 of Carboxylesterases, and 31 of insecticide targets. Orthologs of some of these unigenes have shown to play a pivotal role in insecticide resistance in other insect species and those unigenes likely have similar functions in G. molesta.

Binding Properties of General Odorant Binding Proteins from the Oriental Fruit Moth, Grapholita molesta (Busck) (Lepidoptera: Tortricidae)

Background

The oriental fruit moth Grapholita molesta is a host-switching pest species. The adults highly depend on olfactory cues in locating optimal host plants and oviposition sites. Odorant binding proteins (OBPs) are thought to be responsible for recognizing and transporting hydrophobic odorants across the aqueous sensillum lymph to stimulate the odorant receptors (ORs) within the antennal sensilla and activate the olfactory signal transduction pathway. Exploring the physiological function of these OBPs could facilitate understanding insect chemical communications.

Methodology/Principal Finding

Two antennae-specific general OBPs (GOBPs) of G. molesta were expressed and purified in vitro. The binding affinities of G. molesta GOBP1 and 2 (GmolGOBP1 and 2) for sex pheromone components and host plant volatiles were measured by fluorescence ligand-binding assays. The distribution of GmolGOBP1 and 2 in the antennal sensillum were defined by whole mount fluorescence immunohistochemistry (WM-FIHC) experiments. The binding sites of GmolGOBP2 were predicted using homology modeling, molecular docking and site-directed mutagenesis. Both GmolGOBP1 and 2 are housing in sensilla basiconica and with no differences in male and female antennae. Recombinant GmolGOBP1 (rGmolGOBP1) exhibited broad binding properties towards host plant volatiles and sex pheromone components; rGmolGOBP2 could not effectively bind host plant volatiles but showed specific binding affinity with a minor sex pheromone component dodecanol. We chose GmolGOBP2 and dodecanol for further homology modeling, molecular docking, and site-directed mutagenesis. Binding affinities of mutants demonstrated that Thr9 was the key binding site and confirmed dodecanol bonding to protein involves a hydrogen bond. Combined with the pH effect on binding affinities of rGmolGOBP2, ligand binding and release of GmolGOBP2 were related to a pH-dependent conformational transition.

Conclusion

Two rGmolGOBPs exhibit different binding characteristics for tested ligands. rGmolGOBP1 has dual functions in recognition of host plant volatiles and sex pheromone components, while rGmolGOBP2 is mainly involved in minor sex pheromone component dodecanol perception. This study also provides empirical evidence for the predicted functions of key amino acids in recombinant protein ligand-binding characteristics.

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.

Identification of Host-Plant Volatiles and Characterization of Two Novel General Odorant-Binding Proteins from the Legume Pod Borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae)

Chemoreception is a key feature in selection of host plant by phytophagous insects, and odorant-binding proteins (OBPs) are involved in chemical communication of both insects and vertebrates. The legume pod borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae) is one of the key pest species of cowpea and widely distributed throughout tropical and subtropical regions, causing up to 80% of yield loss. In this study, we investigated the electrophysiological responses of female M. vitrata to floral volatiles from V. unguiculata. Seventeen electroantennogram-active compounds were identified from floral volatiles of V. unguiculata by coupled gas chromatography-electroantennography (GC-EAD) and gas chromatography-mass spectrometry (GC-MS). Then, we cloned two novel full-length GOBP genes (MvitGOBP1 and MvitGOBP2) from the antennae of M. vitrata using reverse transcription PCR. Protein sequence analysis indicated that they shared high sequence similarity with other Pyralididae insect GOBPs and had the typical six-cysteine signature. Real-time PCR analysis indicated that MvitGOBP1-2 mRNA was highly expressed in the antennae of female adult with several thousands-fold difference compare to other tissue. Next, the recombinant MvitGOBP1-2 was expressed in Escherichia coli and purified using Ni ion affinity chromatography. Fluorescence binding assays demonstrated that MvitGOBP1-2 had different binding affinities with 17 volatile odorant molecules including butanoic acid butyl ester, limonene, 4-ethylpropiophenone, 1H-indol-4-ol, butanoic acid octyl ester and 2-methyl-3-phenylpropanal. In the field trapping experiment, these six floral volatiles could effectively attract female moths and showed significant difference compared with the blank lure. These results suggested that MvitGOBPs and the seventeen floral volatiles are likely to function in the olfactory behavior response of female moths, which may have played crucial roles in the selection of oviposition sites. The six compounds that we have identified from the volatiles of V. unguiculata may provide useful information for exploring efficiency monitoring and integrated pest management strategies of this legume pod borer in the field.

Construction and analysis of antennal cDNA library from rice striped stem borer, Chilo suppressalis (Walker) (Lepidoptera: Pyralidae), and expression profiles of putative odorant-binding protein and chemosensory protein genes

In this study, we constructed a high-quality cDNA library from the antennae of the Chilo suppressalis (Walker) (Lepidoptera: Pyralidae). A total of 1,235 colonies with inserts greater than 0.7 kb were sequenced and analyzed. Homology searching coupled with bioinformatics analysis identified 15 and 7 cDNA sequences, respectively, encoding putative odorant-binding proteins (OBPs) and chemosensory proteins (CSPs). A phylogenetic tree of CsupCSPs showed that each CsupCSP has orthologs in Manduca sexta and Bombyx mori with strong bootstrapping support. One CSP was either very specific or more related to the CSPs of another species than to conspecific CSP. The expression profiles of the OBPs and CSPs in different tissues were measured by real-time quantitative PCR. The results revealed that of the 11 OBP genes, the transcript levels of CsupOBP1, CsupOBP5, and CsupOBP7 were higher in both male and female antennae than those in other tissues. And CsupCSP7 was highly expressed in both male and female antennae. Based on these results, the possible physiological functions of CsupOBPs and CsupCSPs were discussed.

Identification and tissue distribution of odorant binding protein genes in the beet armyworm, Spodoptera exigua

Odorant binding proteins (OBPs) contribute to the remarkable sensitivity of the insect's olfactory system and play an important role in insect chemical communication. In this study, we identified 11 putative cDNAs encoding OBPs (namely SexiOBP1-11) from the antennal full length cDNA library of the beet armyworm Spodoptera exigua (Lepidoptera: Noctuidae) and examined their expression profiles in different adult body tissues (antennae, heads, thoraxes, abdomens, legs and wings) by real-time quantitative PCR (qPCR). All SexiOBPs had the characteristic typical features of the OBP family, with the exception of SexiOBP11, which lacked the predicted signal peptide sequence at the N-terminus. qPCR revealed that all of these genes were highly transcribed in the antennae. SexiOBP1-4 and SexiOBP10 were dominantly restricted to antennae. Within antennae, SexiOBP2-4 and SexiOBP10 exhibited female-biased expression patterns, while the expression of SexiOBP7 was male-biased, indicating that they might be involved in interacting with sex pheromones. In general, these OBPs were mainly expressed in chemosensory-specific tissues, although some displayed non-chemosensory or ubiquitous tissue expression. The data is helpful for further determining the potential physiological functions of S. exigua OBPs, and paves the way towards a better understanding of the chemosensory perception of this pest, which may help to uncover new targets for behavioral interference used as a control strategy.