Molecular characterization and expression pattern of two general odorant binding proteins from the diamondback moth, Plutella xylostella

Identification and functional characterization of two antenna-specifc odorant-binding proteins in Plutella xylostella response to 2,3-dimethyl-6-(1-hydroxy)-pyrazine

Plutella xylostella is an important cruciferous crop pest with a serious resistance to multiple insecticides, a novel natural compound, 2,3-dimethyl-6-(1-hydroxy)-pyrazine were isolated, that showed significant repellent activity against P. xylostella with olfactory system as a potential target. Eight odorant-binding proteins (OBPs) were determined as candidate target genes using RT-qPCR (Quantitative reverse transcription PCR), most of them were clustered with OBPs from Spodoptera frugiperda. Fluorescence competitive binding assays showed that PxylPBP2 (Pheromone binding protein) and PxylOBP3 had Ki values of 7.13 ± 0.41 μM and 9.56 ± 0.35 μM, indicating a high binding affinity to the pyrazine. Moreover, the binding style between these two OBPs and the pyrazine was determined as a hydrophobic interaction by using molecular docking. The binding between PxylPBP2 and the pyrazine was found to be more stable, and the carbon atoms of C-2 and C-3 in this pyrazine showed potential optimization characteristics. Both PxylPBP2 and PxylOBP3 were highly expressed in the antennae of both sexes. These results can be used to design and develop novel green pesticides with the pyrazine as the active or lead compound to reduce the utilization of chemical pesticides and postpone development of resistance.

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.

Identification and expression profile of odorant-binding proteins in the parasitic wasp Microplitis pallidipes using PacBio long-read sequencing

Microplitis pallidipes Szépligeti (Hymenoptera: Braconidae) is an important parasitic wasp of second and third-instar noctuid larvae such as the insect pests Spodoptera exigua, Spodoptera litura, and Spodoptera frugiperda. As in other insects, M. pallidipes has a chemosensory recognition system that is critical to foraging, mating, oviposition, and other behaviors. Odorant-binding proteins (OBPs) are important to the system, but those of M. pallidipes have not been determined. This study used PacBio long-read sequencing to identify 170,980 M. pallidipes unigenes and predicted 129,381 proteins. Following retrieval of possible OBP sequences, we removed those that were redundant or non-full-length and eventually cloned five OBP sequences: MpOBP2, MpOBP3, MpOBP8, MpOBP10, and MpPBP 429, 429, 459, 420, and 429 bp in size, respectively. Each M. pallidipes OBP had six conserved cysteine residues. Phylogenetic analysis revealed that the five OBPs were located at different branches of the phylogenetic tree. Additionally, tissue expression profiles indicated that MpOBP2 and MpPBP were mainly expressed in the antennae of male wasps, while MpOBP3, MpOBP8, and MpOBP10 were mainly expressed in the antennae of female wasps. MpOBP3 was also highly expressed in the legs of female wasps. Temporal profiles revealed that the expression of each M. pallidipes OBP peaked at different days after emergence to adulthood. In conclusion, we identified five novel odorant-binding proteins of M. pallidipes and demonstrated biologically relevant differences in expression patterns.

Identification of Genes Involved in Chemoreception in Plutella xyllostella by Antennal Transcriptome Analysis

Perception of environmental and habitat cues is of significance for insect survival and reproduction. Odor detection in insects is mediated by a number of proteins in antennae such as odorant receptors (ORs), ionotropic receptors (IRs), odorant binding proteins (OBPs), chemosensory proteins (CSPs), sensory neuron membrane proteins (SNMPs) and odorant degrading enzymes. In this study, we sequenced and assembled the adult male and female antennal transcriptomes of a destructive agricultural pest, the diamondback moth Plutella xyllostella. In these transcriptomes, we identified transcripts belonging to 6 chemoreception gene families related to ordor detection, including 54 ORs, 16 IRs, 7 gustatory receptors (GRs), 15 CSPs, 24 OBPs and 2 SNMPs. Semi-quantitative reverse transcription PCR analysis of expression patterns indicated that some of these ORs and IRs have clear sex-biased and tissue-specific expression patterns. Our results lay the foundation for future characterization of the functions of these P. xyllostella chemosensory receptors at the molecular level and development of novel semiochemicals for integrated control of this agricultural pest.

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.

AN ODORANT-BINDING PROTEIN INVOLVED IN PERCEPTION OF HOST PLANT ODORANTS IN LOCUST Locusta migratoria

Locusts, Locusta migratoria (Orthoptera: Acrididae), are extremely destructive agricultural pests, but very little is known of their molecular aspects of perception to host plant odorants including related odorant-binding proteins (OBPs), though several OBPs have been identified in locust. To elucidate the function of LmigOBP1, the first OBP identified from locust, RNA interference was employed in this study to silence LmigOBP1, which was achieved by injection of dsRNA targeting LmigOBP1 into the hemolymph of male nymphs. Compared with LmigOBP1 normal nymphs, LmigOBP1 knockdown nymphs significantly decreased food (maize leaf, Zea mays) consumption and electro-antennography responses to five maize leaf volatiles, ((Z)-3-hexenol, linalool, nonanal, decanal, and (Z)-3-hexenyl acetate). These suggest that LmigOBP1 is involved in perception of host plant odorants.

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.

Evidence for trade-offs in detoxification and chemosensation gene signatures in Plutella xylostella

BACKGROUND

Detoxification genes have been associated with insecticide adaptation in the diamondback moth, Plutella xylostella. The link between chemosensation genes and adaptation, however, remains unexplored. To gain a better understanding of the involvement of these genes in insecticide adaptation, the authors exposed lines of P. xylostella to either high uniform (HU) or low heterogeneous (LH) concentrations of permethrin, expecting primarily physiological or behavioral selection respectively. Initially, 454 pyrosequencing was applied, followed by an examination of expression profiles of candidate genes that responded to selection [cytochrome P450 (CYP), glutathione S-transferase (GST), carboxylesterase (CarE), chemosensory protein (CSP) and odorant-binding protein (OBP)] by quantitative PCR in the larvae. Toxicity and behavioral assays were also conducted to document the effects of the two forms of exposure.

RESULTS

Pyrosequencing of the P. xylostella transcriptome from adult heads and third instars produced 198,753 reads with 52,752,486 bases. Quantitative PCR revealed overexpression of CYP4M14, CYP305B1 and CSP8 in HU larvae. OBP13, however, was highest in LH. Larvae from LH and HU lines had up to five- and 752-fold resistance levels respectively, which could be due to overexpression of P450s. However, the behavioral responses of all lines to a series of permethrin concentrations did not vary significantly in any of the generations examined, in spite of the observed upregulation of CSP8 and OBP13.

CONCLUSION

Expression patterns from the target genes provide insights into behavioral and physiological responses to permethrin and suggest a new avenue of research on the role of chemosensation genes in insect adaptation to toxins.

Application of Cydia pomonella expressed sequence tags: Identification and expression of three general odorant binding proteins in codling moth

The codling moth, Cydia pomonella, is one of the most important pests of pome fruits in the world, yet the molecular genetics and the physiology of this insect remain poorly understood. A combined assembly of 8 341 expressed sequence tags was generated from Roche 454 GS-FLX sequencing of eight tissue-specific cDNA libraries. Putative chemosensory proteins (12) and odorant binding proteins (OBPs) (18) were annotated, which included three putative general OBP (GOBP), one more than typically reported for other Lepidoptera. To further characterize CpomGOBPs, we cloned cDNA copies of their transcripts and determined their expression patterns in various tissues. Cloning and sequencing of the 698 nt transcript for CpomGOBP1 resulted in the prediction of a 163 amino acid coding region, and subsequent RT-PCR indicated that the transcripts were mainly expressed in antennae and mouthparts. The 1 289 nt (160 amino acid) CpomGOBP2 and the novel 702 nt (169 amino acid) CpomGOBP3 transcripts are mainly expressed in antennae, mouthparts, and female abdomen tips. These results indicate that next generation sequencing is useful for the identification of novel transcripts of interest, and that codling moth expresses a transcript encoding for a new member of the GOBP subfamily.

Functional analysis of general odorant binding protein 2 from the meadow moth, Loxostege sticticalis L. (Lepidoptera: Pyralidae)

Odorant binding proteins play a crucial role in transporting semiochemicals across the sensillum lymph to olfactory receptors within the insect antennal sensilla. In this study, the general odorant binding protein 2 gene was cloned from the antennae of Loxostege sticticalis, using reverse transcription PCR and rapid amplification of cDNA ends. Recombinant LstiGOBP2 was expressed in Escherichia coli and purified by Ni ion affinity chromatography. Real-time PCR assays indicated that LstiGOBP2 mRNA is expressed mainly in adult antennae, with expression levels differing with developmental age. Ligand-binding experiments using N-phenyl-naphthylamine (1-NPN) as a fluorescent probe demonstrated that the LstiGOBP2 protein has binding affinity to a broad range of odorants. Most importantly, trans-11-tetradecen-1-yl acetate, the pheromone component of Loxostege sticticalis, and trans-2-hexenal and cis-3-hexen-1-ol, the most abundant plant volatiles in essential oils extracted from host plants, had high binding affinities to LstiGOBP2 and elicited strong electrophysiological responses from the antennae of adults.

General guidelines for authors for submission of manuscripts that contain molecular biological content

The Journal of Chemical Ecology (the Journal) has been publishing an increasing number of contributions that report experiments that use the methods of molecular biology. In 2004, a special issue of the Journal [JCE 30(12)] focused on molecular chemical ecology and documented the increasing trend of published submissions with molecular content (Seybold 2004). The guidelines presented here were developed to provide assistance to authors, with the goal of ensuring standardized and complete reporting of molecular information in the Journal. The fields of molecular biology and bioinformatics change rapidly as new technologies and protocols are continually developed and introduced. Thus, the Journal intends to revise and re-issue these guidelines periodically as significant changes in this area of science occur. Molecular biological content includes reports on specific nucleic acids and proteins involved in chemical ecological phenomena. The guidelines are separated into 3 parts: I. Types of Papers Published; II. Appropriate Nomenclature and Abbreviations; and III. Presentation of Molecular Biological Content.

Construction and analysis of cDNA libraries from the antennae of male and female cotton bollworms Helicoverpa armigera (Hübner) and expression analysis of putative odorant-binding protein genes

Two high-quality cDNA libraries were constructed from female and male antennae of the cotton bollworm Helicoverpa armigera (Hübner). The titers were approximately 2.0 × 10⁶ pfu/ml for females and 2.3 × 10⁶ pfu/ml for males, and this complies with the test requirement. From the libraries, 1750 male ESTs and 1640 female ESTs were sequenced and further analyzed. We identified 15 olfactory genes (12 are new), and 14 of them have the characteristic six conserved cysteine residues. With the exception of OBP9, all the genes were classified as classical OBP genes. By alignment and cluster analysis, the 14 classical OBPs were divided into pheromone binding protein (PBP) genes, odorant binding protein (OBP) genes, general odorant binding protein 1 (GOBP1) genes, general odorant binding protein 2 (GOBP2) genes and antennae binding protein (ABP) genes. Among these genes, we obtained three PBP genes (PBP1-PBP3) including two new PBP genes, one new ABP gene, nine new OBP genes (OBP1-OBP9), one known GOBP1 gene and one known GOBP2 gene. Furthermore, the expression patterns of these 14 classical OBP genes were investigated in various tissues by real-time quantitative polymerase chain reaction (qPCR). The results indicated that some OBP genes are expressed differently in different sexes and tissues, but most of them are highly expressed in antennae.

Molecular characterization and expression pattern of four chemosensory proteins from diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Some chemosensory proteins (CSPs) expressed in insect sensory appendages are thought to be involved in chemical signaling in moths. We cloned and characterized four CSP genes from Plutella xylostella. The deduced amino acid sequences of PxylCSP1, PxylCSP2, PxylCSP3 and PxylCSP4 revealed open reading frames of 152, 128, 126 and 126 amino acids, respectively, with four conserved cysteine residues. The expression patterns of the four PxylCSP genes were further investigated by reverse transcription (RT) PCR and real-time PCR. PxylCSP1 and PxylCSP2 genes were expressed in all the tested tissues with the highest expression level in the antennae and heads (without antennae) whereas PxylCSP3 and PxylCSP4 mRNA were distributed extensively in all the tested tissues without apparent quantitative differences. The transcription levels of these CSP genes depended on sex, age, mating and the genes. Fluorescence quenching with Rhodojaponin-III (R-III) and homology modelling studies indicated that PxylCSP1 was able to bind non-volatile oviposition deterrents, such as R-III. These ubiquitous proteins might have the role of extracting non-volatile compounds (oviposition deterrents or antifeedants) dispersed in the environment and transporting them to their receptor.