Proteomic analysis of brown planthopper: application to the study of carbamate toxicity

Gene expression changes in Maconellicoccus hirsutus in response to sublethal dose of buprofezin

The pink or hibiscus mealybug, Maconellicoccus hirsutus, is a serious pest of grapes, jute, and mesta, causing severe yield losses in India and other countries. Chemical control remains the foremost choice for farmers to manage this pest. As insecticides break down over time due to biotic and abiotic factors, insects are exposed to varying levels of these exogenous compounds. Several studies have reported that sublethal doses affect insect physiology, but only a few have examined the changes in gene expression at the molecular level. Therefore, the present study was conducted to elucidate the molecular mechanisms in M. hirsutus exposed to sublethal doses of buprofezin 25 SC. Life table analysis revealed increased fecundity in M. hirsutus exposed to the sublethal dose. A total of 1,744 differentially expressed genes were identified between the buprofezin-treated and untreated samples using transcriptome analysis. These genes were primarily associated with ribosomal proteins, proteases, cuticular proteins, and cytoskeletal structures. Ribosomes and phagosomes were the most highly enriched pathways. Interestingly, most of the DEGs were involved in restoring homeostasis rather than detoxification. To validate our RNA-sequencing results, qRT-PCR validation was performed on ten randomly selected genes. Overall, our findings provide valuable insights into intermittent changes in stress-coping genes, apart from detoxification genes.

Comparative proteomics reveals mechanisms that underlie insecticide resistance in Culex pipiens pallens Coquillett

Mosquito control based on chemical insecticides is considered as an important element of the current global strategies for the control of mosquito-borne diseases. Unfortunately, the development of insecticide resistance of important vector mosquito species jeopardizes the effectiveness of insecticide-based mosquito control. In contrast to target site resistance, other mechanisms are far from being fully understood. Global protein profiles among cypermethrin-resistant, propoxur-resistant, dimethyl-dichloro-vinyl-phosphate-resistant and susceptible strain of Culex pipiens pallens were obtained and proteomic differences were evaluated by using isobaric tags for relative and absolute quantification labeling coupled with liquid chromatography/tandem mass spectrometric analysis. A susceptible strain of Culex pipiens pallens showed elevated resistance levels after 25 generations of insecticide selection, through iTRAQ data analysis detected 2,502 proteins, of which 1,513 were differentially expressed in insecticide-selected strains compared to the susceptible strain. Finally, midgut differential protein expression profiles were analyzed, and 62 proteins were selected for verification of differential expression using iTRAQ and parallel reaction monitoring strategy, respectively. iTRAQ profiles of adaptation selection to three insecticide strains combined with midgut profiles revealed that multiple insecticide resistance mechanisms operate simultaneously in resistant insects of Culex pipiens pallens. Significant molecular resources were developed for Culex pipiens pallens, potential candidates were involved in metabolic resistance and reducing penetration or sequestering insecticide. Future research that is targeted towards RNA interference of the identified metabolic targets, such as cuticular proteins, cytochrome P450s, glutathione S-transferases and ribosomal proteins proteins and biological pathways (drug metabolism—cytochrome P450, metabolism of xenobiotics by cytochrome P450, oxidative phosphorylation, ribosome) could lay the foundation for a better understanding of the genetic basis of insecticide resistance in Culex pipiens pallens.

Global protein profiles were compared among a susceptible strain of Cx. pipiens pallens and strains that were cypermethrin-resistant, propoxur-resistant, and dimethyl-dichloro-vinyl-phosphate-resistant after 25 generations of selection by distinct chemical insecticide families, multiple mechanisms were found to operate simultaneously in resistant mosquitoes of Cx. pipiens pallens, including mechanisms to lower penetration of or sequester the insecticide or to increase biodegradation of the insecticide via subtle alterations in either the cuticular protein levels or the activities of detoxification enzymes (P450s and glutathione S-transferases).

Proteomic Analyses Detect Higher Expression of C-Type Lectins in Imidacloprid-Resistant Colorado Potato Beetle Leptinotarsa decemlineata Say

Simple Summary

Surveillance and determining the mechanisms of pesticide resistance are key components of resistance management. Mechanisms can be investigated using biochemical, genomic, proteomic and other modern analytical techniques. In the present study, proteomic analyses of Colorado potato beetle (CPB), one of the most adaptable insect pests to both plant toxins and synthetic insecticides, were applied to identify protein differences in insecticide-susceptible and resistant strains. Proteins identified in abdominal and midgut tissues based on separating by 2-dimensional (2-D) gels and mass spectrometry were associated with insect innate immunity. A database search found that the highest match was a C-type lectin (CTL), which is a component in the insect’s innate immune system. The 2-D gel spot identified as a CTL was greater in the insecticide-resistant CPB strain, but the CTL spot size was increased by exposure to imidacloprid in the susceptible strain. This is a novel finding, which suggests that CTLs and insect immunity may respond to certain toxins as well as to pathogens. There may also be a potential application for pest management if insect immunity is targeted.

Abstract

The Colorado potato beetle (CPB) is one of the most adaptable insect pests to both plant toxins and synthetic insecticides. Resistance in CPB is reported for over 50 classes of insecticides, and mechanisms of insecticide-resistance include enhanced detoxification enzymes, ABC transporters and target site mutations. Adaptation to insecticides is also associated with changes in behaviour, energy metabolism and other physiological processes seemingly unrelated to resistance but partially explained through genomic analyses. In the present study, in place of genomics, we applied 2-dimensional (2-D) gel and mass spectrometry to investigate protein differences in abdominal and midgut tissue of insecticide-susceptible (S) and -resistant (R) CPB. The proteomic analyses measured constitutive differences in several proteins, but the highest match was identified as a C-type lectin (CTL), a component of innate immunity in insects. The constitutive expression of the CTL was greater in the multi-resistant (LI) strain, and the same spot was measured in both midgut and abdominal tissue. Exposure to the neonicotinoid insecticide, imidacloprid, increased the CTL spot found in the midgut but not in the abdominal tissue of the laboratory (Lab) strain. No increase in protein levels in the midgut tissue was observed in the LI or a field strain (NB) tolerant to neonicotinoids. With the exception of biopesticides, such as Bacillus thuringiensis (Bt), no previous studies have documented differences in the immune response by CTLs in insects exposed to synthetic insecticides or the fitness costs associated with expression levels of immune-related genes in insecticide-resistant strains. This study demonstrates again how CPB has been successful at adapting to insecticides, plant defenses as well as pathogens.

Time-dependent stress evidence in dynamic allocation of physiological metabolism of Nilaparvata lugens in response to elevated CO2

To assess the time-dependent stress evidence in dynamic allocation of physiological metabolism of Nilaparvata lugens nymphs in response to elevated CO₂, we measured the time-dependent allocation of nutrient compositions and physiological metabolism in the bodies of N. lugens at 1h, 4h and 12h under elevated CO₂. Elevated CO₂ significantly increased the contents of nutrient compositions (protein, glucose and total amino acids) and catalase (CAT) enzyme activity in the body of N. lugens at 12h relative to 1h and 4h (P < 0.05). Significantly higher genes expression levels of acetylcholinesterase (AChE), heat shock protein (HSP70) and vitellogenin gene (vg) were observed in the body of N. lugens compared with those in ambient CO₂ at 4h (P < 0.05). These results showed that there was an instantaneous reaction of N. lugens nymphs to elevated CO₂, which indicated N. lugens may enhance stress defense response to future increasing CO₂ levels.

Pesticide-Induced Planthopper Population Resurgence in Rice Cropping Systems

Planthoppers are serious rice pests in Asia. Their population resurgence was first reported in the early 1960s, caused mainly by insecticides that indiscriminately killed beneficial arthropods and target pests. The subsequent resurgence involved two mechanisms, the loss of beneficial insects and insecticide-enhanced planthopper reproduction. In this review, we identify two forms of resurgence, acute and chronic. Acute resurgence is caused by traditional insecticides with rapid resurgence in the F₁ generation. Chronic resurgence follows application of modern pesticides, including fungicides and herbicides, with low natural enemy toxicity, coupled with stimulated planthopper reproduction. The chemical-driven syndrome of changes leads to later resurgence in the F₂ or later generations. Chronic resurgence poses new threats to global rice production. We review findings on the physiological and molecular mechanisms of chronic planthopper resurgence and suggest research directions that may help manage these new threats.

Design, synthesis, and insecticidal activity evaluation of novel 4-(N, N-diarylmethylamines)furan-2(5H)-one derivatives as potential acetylcholine receptor insecticides

BACKGROUND

Flupyradifurone is a member of a novel class of insecticides that possess excellent insecticidal activities. Halogen-containing phenyl groups are important and indispensable structural components of many pesticides. However, replacement of the difluoromethyl group of flupyradifurone with halogen-containing phenyl groups has not been reported. Hence, a series of novel butenolide derivatives containing phenyl groups were synthesized and bioassayed to discover novel compounds with excellent insecticidal activities.

RESULTS

Some target molecules exhibited good insecticidal activities against Aphis craccivora. Among the title compounds, 4cc showed the best insecticidal activities with an 50% lethal concentration (LC₅₀ ) value of 1.72 μg mL^-1 , which is superior to that of pymetrozine (LC₅₀  = 6.86 μg mL^-1 ). Molecular docking indicated that 4cc lacks oxidative metabolism by CYP6CM1 and metabolic resistance with imidacloprid. Furthermore, label-free quantitative proteomic analysis indicated that 4cc may be a potential acetylcholine receptor insecticide that acts on the nicotinic acetylcholine receptor. Compound 4cc also decreased the capability for oxidative metabolism, which further supported the molecular docking results.

CONCLUSION

This work can be used to further investigate the mechanism underlying the insecticidal activity of butenolide derivatives and develop potential novel butenolide insecticides. © 2018 Society of Chemical Industry.

Synthesis and Insecticidal Activity of Mesoionic Pyrido[1,2-α]pyrimidinone Derivatives Containing a Neonicotinoid Moiety

Mesoionic pyrido[1,2-α]pyrimidinone derivatives containing a neonicotinoid moiety were designed, synthesized, and evaluated for their insecticidal activity. Some of the title compounds showed remarkable insecticidal properties against Aphis craccivora. Compound I13 exhibited satisfactory insecticidal activity against A. craccivora. Meanwhile, label-free proteomics analysis of compound I13 treatment identified a total of 821 proteins. Of these, 35 proteins were up-regulated, whereas 108 proteins were down-regulated. Differential expressions of these proteins reflected a change in cellular structure and metabolism.

Dynamic metabolic responses of brown planthoppers towards susceptible and resistant rice plants

Brown planthopper (Nilaparvata lugens Stål, BPH) causes huge economic losses in rice-growing regions, and new strategies for combating BPH are required. To understand how BPHs respond towards BPH-resistant plants, we systematically analysed the metabolic differences between BPHs feeding on the resistant and susceptible plants using NMR and GC-FID/MS. We also measured the expression of some related genes involving glycolysis and biosyntheses of trehalose, amino acids, chitin and fatty acids using real-time PCR. BPH metabonome was dominated by more than 60 metabolites including fatty acids, amino acids, carbohydrates, nucleosides/nucleotides and TCA cycle intermediates. After initial 12 h, BPHs feeding on the resistant plants had lower levels of amino acids, glucose, fatty acids and TCA cycle intermediates than on the susceptible ones. The levels of these metabolites recovered after 24 h feeding. This accompanied with increased level in trehalose, choline metabolites and nucleosides/nucleotides compared with BPH feeding on the susceptible plants. Decreased levels of BPH metabolites at the early feeding probably resulted from less BPH uptakes of sap from resistant plants and recovery of BPH metabolites at the later stage probably resulted from their adaptation to the adverse environment with their increased hopping frequency to ingest more sap together with contributions from yeast-like symbionts in BPHs. Throughout 96 h, BPH feeding on the resistant plants showed significant up-regulation of chitin synthase catalysing biosynthesis of chitin for insect exoskeleton, peritrophic membrane lining gut and tracheae. These findings provided useful metabolic information for understanding the BPH-rice interactions and perhaps for developing new BPH-combating strategies.

Assessing the relevance of a multiplexed methodology for proteomic biomarker measurement in the invertebrate species Gammarus fossarum: A physiological and ecotoxicological study

Recently, a protein sequence database was built specifically for the sentinel non-model species Gammarus fossarum using a proteogenomics approach. A quantitative multiplexed targeted proteomics assay (using Selected Reaction Monitoring mass spectrometry) was then developed for a fast and simultaneous quantification of dozens of biomarker peptides specific of this freshwater sentinel crustacean species. In order to assess the relevance of this breakthrough methodology in ecotoxicology, the response patterns of a panel of 26 peptides reporting for 20 proteins from the Gammarus fossarum proteome with putative key functional roles (homeostasis, osmoregulation, nutrition, reproduction, molting,…) were recorded through male and female reproductive cycles and after exposure to environmental concentrations of cadmium and lead in laboratory-controlled conditions. Based on these results, we validated the implication of annotated vtg-like peptides in the oogenesis process, and the implication of Na⁺/K⁺ ATPase proteins in the molt cycle of organisms. Upon metal (cadmium and lead) contamination, peptides belonging to proteins annotated as involved in antioxidant and detoxification functions, immunity and molting were significantly down-regulated. Overall, this multiplex assay allowed gaining relevant insights upon disruption of different main functions in the sentinel species Gammarus fossarum. This breakthrough methodology in ecotoxicology offers a valid and high throughput alternative to currently used protocols, paving the way for future practical applications of proteogenomics-derived protein biomarkers in chemical risk assessment and environmental monitoring.

Identification of responsive proteins in Panonychus citri exposed to abamectin by a proteomic approach

Abamectin is a microbial-derived pesticide widely used for control of agricultural pests. However, sustained use of abamectin has led to the development of resistance in some target species. Previous studies on arthropod resistance to abamectin have mainly used traditional biochemical and molecular approaches. To understand the responses of citrus red mite, Panonychus citri, exposed to abamectin, comparative proteomic analysis was conducted using two-dimensional electrophoresis (2-DE). A total of 26 distinct protein spots were present in response to abamectin exposure. Tandem mass spectrometry (MS/MS) identified 16 proteins that were mainly involved in energy metabolism and detoxification. Some remaining proteins were not identifiable, suggesting that they may be novel. The expression levels of transcripts associated with proteins were analyzed by quantitative reverse transcription PCR (qRT-PCR). Furthermore, to validate the proteomic data obtained in the present study, Western-blot experiment was performed and the expression of sHsp and PcE1 proteins were confirmed, respectively.

BIOLOGICAL SIGNIFICANCE

The citrus red mite has developed resistance to many acaricides, including abamectin. In the current study, we used the proteomic approaches involving 2-DE, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF), and MS/MS to document changes in adult P. citri during 24h of abamectin exposure. Abamectin stress induced a total of 16 differentially regulated proteins. The proteomic results were validated in mRNA expression patterns using qRT-PCR. This is the first analysis of differentially expressed proteins in P. citri exposed to abamectin. The results help clarify the physiological mechanisms of P. citri responses to abamectin exposure.

Comparative proteomic analysis in Aphis glycines Mutsumura under lambda-cyhalothrin insecticide stress

Lambda-cyhalothrin is now widely used in China to control the soybean aphid Aphis glycines. To dissect the resistance mechanism, a laboratory-selected resistant soybean aphid strain (CRR) was established with a 43.42-fold resistance ratio to λ-cyhalothrin than the susceptible strain (CSS) in adult aphids. In this study, a comparative proteomic analysis between the CRR and CSS strains revealed important differences between the susceptible and resistant strains of soybean aphids for λ-cyhalothrin. Approximately 493 protein spots were detected in two-dimensional polyacrylamide gel electrophoresis (2-DE). Thirty-six protein spots displayed differential expression of >2-fold in the CRR strain compared to the CSS strain. Out of these 36 protein spots, 21 had elevated and 15 had decreased expression. Twenty-four differentially expressed proteins were identified by MALDI TOF MS/MS and categorized into the functional groups cytoskeleton-related protein, carbohydrate and energy metabolism, protein folding, antioxidant system, and nucleotide and amino acid metabolism. Function analysis showed that cytoskeleton-related proteins and energy metabolism proteins have been associated with the λ-cyhalothrin resistance of A. glycines. The differential expression of λ-cyhalothrin responsive proteins reflected the overall change in cellular structure and metabolism after insecticide treatment in aphids. In summary, our studies improve understanding of the molecular mechanism resistance of soybean aphid to lambda-cyhalothrin, which will facilitate the development of rational approaches to improve the management of this pest and to improve the yield of soybean.

Invited Review: Toxicoproteomics: Proteomics Applied to Toxicology and Pathology

Global measurement of proteins and their many attributes in tissues and biofluids defines the field of proteomics. Toxicoproteomics, as part of the larger field of toxicogenomics, seeks to identify critical proteins and pathways in biological systems that are affected by and respond to adverse chemical and environmental exposures using global protein expression technologies. Toxicoproteomics integrates 3 disciplinary areas: traditional toxicology and pathology, differential protein and gene expression analysis, and systems biology. Key topics to be reviewed are the evolution of proteomics, proteomic technology platforms and their capabilities with exemplary studies from biology and medicine, a review of over 50 recent studies applying proteomic analysis to toxicological research, and the recent development of databases designed to integrate -Omics technologies with toxicology and pathology. Proteomics is examined for its potential in discovery of new biomarkers and toxicity signatures, in mapping serum, plasma, and other biofluid proteomes, and in parallel proteomic and transcriptomic studies. The new field of toxicoproteomics is uniquely positioned toward an expanded understanding of protein expression during toxicity and environmental disease for the advancement of public health.

The expression of proteins involved in digestion and detoxification are regulated in Helicoverpa armigera to cope up with chlorpyrifos insecticide

Helicoverpa armigera is a key pest in many vital crops, which is mainly controlled by chemical strategies. To manage this pest is becoming challenging due to its ability and evolution of resistance against insecticides. Further, its subsequent spread on nonhost plant is remarkable in recent times. Hence, decoding resistance mechanism against phytochemicals and synthetic insecticides is a major challenge. The present work describes that the digestion, defense and immunity related enzymes are associated with chlorpyrifos resistance in H. armigera. Proteomic analysis of H. armigera gut tissue upon feeding on chlorpyrifos containing diet (CH) and artificial diet (AD) using nano-liquid chromatography-mass spectrometry identified upregulated 23-proteins in CH fed larvae. Database searches combined with gene ontology analysis revealed that the identified gut proteins engrossed in digestion, proteins crucial for immunity, adaptive responses to stress, and detoxification. Biochemical and quantitative real-time polymerase chain reaction analysis of candidate proteins indicated that insects were struggling to get nutrients and energy in presence of CH, while at the same time endeavoring to metabolize chlorpyrifos. Moreover, we proposed a potential processing pathway of chlorpyrifos in H. armigera gut by examining the metabolites using gas chromatography-mass spectrometry. H. armigera exhibit a range of intriguing behavioral, morphological adaptations and resistance to insecticides by regulating expression of proteins involved in digestion and detoxification mechanisms to cope up with chlorpyrifos. In these contexts, as gut is a rich repository of biological information; profound analysis of gut tissues can give clues of detoxification and resistance mechanism in insects.

Comparative proteomic analysis of Bactrocera dorsalis (Hendel) in response to thermal stress

Temperature is one of the most important environmental variables affecting growth, reproduction and distribution of insects. The rise of comparative proteomics provides a powerful tool to explore the response in proteins to thermal stress. As an important worldwide pest, the oriental fruit fly Bactrocera dorsalis causes severe economic losses to crops. To understand the response of B. dorsalis to thermal stress, we performed a comparative proteome analysis of this insect after exposure to extreme low and high temperatures using two-dimensional electrophoresis. Among the separated proteins, 51 diverse protein spots were present differently in response to extreme temperatures. Using tandem mass spectrometry sequencing analysis 39 proteins were successfully identified, which included 13 oxidoreductases, 10 binding proteins, 5 transferases, and 2 each of lyases, isomerases, ligases, and developmental proteins. Subsequently, the expression of these protein transcripts was studied by RT-qPCR to validate the proteomic results. In conclusion, this study provides a first look into the thermal stress response of B. dorsalis at the protein level, and thus it paves the way for further functional studies in the physiological mechanism related to thermal stress.

Differential protein expression in the susceptible and resistant Myzus persicae (Sulzer) to imidacloprid

Myzus persicae, a serious economic agricultural pest, has developed resistance to imidacloprid (IMI), which was widely used to control this aphid worldwide. To gain a better understanding of the mechanisms of IMI resistance in M. persicae, we carried out a comparative proteomic analysis. Total proteins of the IMI-susceptible and resistant strains were extracted and separated by two-dimensional gel electrophoresis. More than 1300 protein spots were reproducibly detected, including 14 that were more abundant and 14 less abundant. Mass spectrometry analysis and database searching helped us to identify 25 differentially abundant proteins. The identified proteins were categorized into several functional groups including signal transduction, RNA processing, protein processing, transport processing, stress response, metabolisms, and cytoskeleton structure, etc. This study is the first analysis of differentially expressed proteins in IMI-susceptible and resistant M. Persicae, and gives new insights into the mechanisms of IMI resistance in M. persicae.

Differential expression of hemolymph proteins between susceptible and insecticide-resistant Blattella germanica (Blattodea: Blattellidae)

A proteomic approach combining two-dimensional polyacrylamide gel electrophoresis and tandem mass spectrometry was used to compare hemolymph expression profiles of a beta-cypermethrin-resistant Blattella germanica L. strain and a beta-cypermethrin-susceptible strain. Twenty-eight hemolymph proteins were differentially expressed in the resistant cockroach strain; 19 proteins were upregulated and 9 proteins were downregulated compared with the susceptible strain. Protein identification indicated that expression of putative cuticular protein, nitric oxide synthase, triosephosphate isomerase, alpha-amylase, ABC transporter, and Per a 3 allergen was elevated, and expression of arginine kinase and glycosidase was reduced. The differential expression of these proteins reflects the overall change in cellular structure and metabolism related to the resistance of pyrethroid insecticides.

Proteomic analysis of insecticide triazophos-induced mating-responsive proteins of Nilaparvata lugens Stål (Hemiptera: Delphacidae)

The brown planthopper, Nilaparvata lugens (Stål) (Hemiptera: Delphacidae), is a classic example of a resurgent pest induced by insecticides. It has been demonstrated that triazophos treatment causes an increase in the content of male accessory gland proteins (Acps) that can be transferred to females via mating, influencing female reproduction. However, the mechanism of this type of insecticide-induced Acps in males and the subsequent stimulation of reproduction in females are not well understood. To identify changes in the types of Acps and reproductive proteins in mated females, we conducted a comparative proteomic analysis. Six samples were categorized into four different groups: (1) untreated unmated males compared to treated unmated males (UUM vs TUM); (2) treated unmated males compared to treated mated males (TUM vs TMM); (3) untreated unmated females compared to treated unmated females (UUF vs TUF); (4) treated unmated females compared to treated mated females (TUF vs TMF). Protein expression changes among the four different groups were examined by two-dimensional gel electrophoresis (2-DE) and liquid chromatography tandem mass spectrometry (LC-MS/MS). Of the 500-600 reproducibly detected protein spots on each gel, 107 protein spots were differentially expressed between the four different groups. Of the 63 proteins identified by LC-MS/MS analysis, 38 were up-regulated and 25 were down-regulated in the four different groups. Some novel proteins related to fecundity were observed including spermatogenesis-associated protein 5, testis development protein NYD-SP6, arginine kinase, actin-5C, vitellogenin, and ovarian serine protease nudel. The elevated expression of novel fecundity proteins in six samples of N. lugens females and males due to exposure to triazophos was confirmed by quantitative real-time PCR (qRT-PCR). The results suggest that these proteins may participate in the reproductive process of N. lugens adult females and males. Our findings fill a gap in understanding the relationship between insecticide-treated males and the stimulated reproduction of N. lugens females.

Proteins in ecotoxicology - how, why and why not?

The growing interest in the application of proteomic technologies to solve toxicology issues and its relevance in ecotoxicology research has resulted in the emergence of "ecotoxicoproteomics". There is a general consensus that ecotoxicoproteomics is a powerful tool to spot early molecular events involved in toxicant responses, which are responsible for the adverse effects observed at higher levels of biological organization, thus contributing to elucidate the mode of action of stressors and to identify specific biomarkers. Ultimately, early-warning indicators can then be developed and deployed in "in situ" bioassays and in environmental risk assessment. The number of field experiments or laboratory trials using ecologically relevant test-species and involving proteomics has been, until recently, insufficient to allow a critical analysis of the real benefits of the application of this approach to ecotoxicology. This article intends to present an overview on the applications of proteomics in the context of ecotoxicology, focusing mainly on the prospective research to be done in invertebrates. Although these represent around 95% of all animal species and in spite of the key structural and functional roles they play in ecosystems, proteomic research in invertebrates is still in an incipient stage. We will review applications of ecotoxicoproteomics by evaluating the technical methods employed, the organisms and the contexts studied, the advances achieved until now and lastly the limitations yet to overcome will be discussed.

Tritrophic interactions among Macrosiphum euphorbiae aphids, their host plants and endosymbionts: investigation by a proteomic approach

The Mi-1.2 gene in tomato confers resistance against certain clones of the potato aphid (Macrosiphum euphorbiae). This study used 2D-DIGE coupled with protein identification by MALDI-TOF-MS to compare the proteome patterns of avirulent and semivirulent potato aphids and their bacterial endosymbionts on resistant (Mi-1.2+) and susceptible (Mi-1.2-) tomato lines. Avirulent aphids had low survival on resistant plants, whereas the semivirulent clone could colonize these plants. Eighty-two protein spots showed significant quantitative differences among the four treatment groups, and of these, 48 could be assigned putative identities. Numerous structural proteins and enzymes associated with primary metabolism were more abundant in the semivirulent than in the avirulent aphid clone. Several proteins were also up-regulated in semivirulent aphids when they were transferred from susceptible to resistant plants. Nearly 25% of the differentially regulated proteins originated from aphid endosymbionts and not the aphid itself. Six were assigned to the primary endosymbiont Buchnera aphidicola, and 5 appeared to be derived from a Rickettsia-like secondary symbiont. These results indicate that symbiont expression patterns differ between aphid clones with differing levels of virulence, and are influenced by the aphids' host plant. Potentially, symbionts may contribute to differential adaptation of aphids to host plant resistance.

Proteome changes in the plasma of Papilio xuthus (Lepidoptera: Papilionidae): effect of parasitization by the endoparasitic wasp Pteromalus puparum (Hymenoptera: Pteromalidae)

Although the biochemical dissection of parasitoid-host interactions is becoming well characterized, the molecular knowledge concerning them is minimal. In order to understand the molecular bases of the host immune response to parasitoid attack, we explored the response of Papilio xuthus parasitized by the endoparasitic wasp Pteromalus puparum using proteomic approach. By examining the differential expression of plasma proteins in the parasitized and unparasitized host pupae by two-dimensional (2D) electrophoresis, 16 proteins were found to vary in relation to parasitization compared with unparasitized control samples. All of them were submitted to identification by mass spectrometry coupled with a database search. The modulated proteins were found to fall into the following functional groups: humoral or cellular immunity, detoxification, energy metabolism, and others. This study contributes insights into the molecular mechanism of the relationships between parasitoids and their host insects.

Annotated ESTs from various tissues of the brown planthopper Nilaparvata lugens: a genomic resource for studying agricultural pests

Background

The brown planthopper (BPH), Nilaparvata lugens (Hemiptera, Delphacidae), is a serious insect pests of rice plants. Major means of BPH control are application of agricultural chemicals and cultivation of BPH resistant rice varieties. Nevertheless, BPH strains that are resistant to agricultural chemicals have developed, and BPH strains have appeared that are virulent against the resistant rice varieties. Expressed sequence tag (EST) analysis and related applications are useful to elucidate the mechanisms of resistance and virulence and to reveal physiological aspects of this non-model insect, with its poorly understood genetic background.

Results

More than 37,000 high-quality ESTs, excluding sequences of mitochondrial genome, microbial genomes, and rDNA, have been produced from 18 libraries of various BPH tissues and stages. About 10,200 clusters have been made from whole EST sequences, with average EST size of 627 bp. Among the top ten most abundantly expressed genes, three are unique and show no homology in BLAST searches. The actin gene was highly expressed in BPH, especially in the thorax. Tissue-specifically expressed genes were extracted based on the expression frequency among the libraries. An EST database is available at our web site.

Conclusion

The EST library will provide useful information for transcriptional analyses, proteomic analyses, and gene functional analyses of BPH. Moreover, specific genes for hemimetabolous insects will be identified. The microarray fabricated based on the EST information will be useful for finding genes related to agricultural and biological problems related to this pest.

Proteomic applications in ecotoxicology

Within the growing body of proteomics studies, issues addressing problems of ecotoxicology are on the rise. Generally speaking, ecotoxicology uses quantitative expression changes of distinct proteins known to be involved in toxicological responses as biomarkers. Unlike these directed approaches, proteomics examines how multiple expression changes are associated with a contamination that is suspected to be detrimental. Consequently, proteins involved in toxicological responses that have not been described previously may be revealed. Following identification of key proteins indicating exposure or effect, proteomics can potentially be employed in environmental risk assessment. To this end, bioinformatics may unveil protein patterns specific to an environmental stress that would constitute a classifier able to distinguish an exposure from a control state. The combined use of sets of marker proteins associated with a given pollution impact may prove to be more reliable, as they are based not only on a few unique markers which are measured independently, but reflect the complexity of a toxicological response. Such a proteomic pattern might also integrate some of the already established biomarkers of environmental toxicity. Proteomics applications in ecotoxicology may also comprise functional examination of known classes of proteins, such as glutathione transferases or metallothioneins, to elucidate their toxicological responses.

Proteomic profiling of aphid Macrosiphum euphorbiae responses to host-plant-mediated stress induced by defoliation and water deficit

Abiotic and biotic host-plant stress, such as desiccation and herbivory, may strongly affect sap-sucking insects such as aphids via changes in plant chemicals of insect nutritional or plant defensive value. Here, we examined (i) water deprivation and (ii) defoliation by the beetle Leptinotarsa decemlineata as stresses indirectly affecting the aphid Macrosiphum euphorbiae via its host plant Solanum tuberosum. For plant-induced stress, aphids were reared on healthy vs. continuously stressed potato for 14 days (no watering; defoliation maintained at approximately 40%). Aphid performance under stress was correlated with metabolic responses monitored by profiling of the aphid proteome. M. euphorbiae was strongly affected by water stress, as adult survival, total aphid number and biomass were reduced by 67%, 64%, and 79%, respectively. Aphids performed normally on defoliated potato, indicating that they were unaffected or able to compensate any stress induced by plant defoliation. Stressed aphid proteomes revealed 419-453 protein spots, including 27 that were modulated specifically or jointly under each kind of host-plant stress. Reduced aphid fitness on water-stressed plants mostly correlated with modulation of proteins involved in energy metabolism, apparently to conserve energy in order to prioritize survival. Despite normal performance, several aphid proteins that are known to be implicated in cell communication were modulated on defoliated plants, possibly suggesting modified aphid behaviour. The GroEL protein (or symbionin) of the endosymbiont Buchnera aphidicola was predominant under all conditions in M. euphorbiae. Its expression level was not significantly affected by aphid host-plant stresses, which is consistent with the high priority of symbiosis in stressed aphids.

Proteomics in Myzus persicae: effect of aphid host plant switch

Chemical ecology is the study of how particular chemicals are involved in interactions of organisms with each other and with their surroundings. In order to reduce insect attack, plants have evolved a variety of defence mechanisms, both constitutive and inducible, while insects have evolved strategies to overcome these plant defences (such as detoxification enzymes). A major determinant of the influence of evolutionary arms races is the strategy of the insect: generalist insect herbivores, such as Myzus persicae aphid, need more complex adaptive mechanisms since they need to respond to a large array of different plant defensive chemicals. Here we studied the chemical ecology of M. persicae associated with different plant species, from Brassicaceae and Solanaceae families. To identify the involved adaptation systems to cope with the plant secondary substances and to assess the differential expression of these systems, a proteomic approach was developed. A non-restrictive approach was developed to identify all the potential adaptation systems toward the secondary metabolites from host plants. The complex protein mixtures were separated by two-dimensional electrophoresis methods and the related spots of proteins significantly varying were selected and identified by mass spectrometry (ESI MS/MS) coupled with data bank investigations. Fourteen aphid proteins were found to vary according to host plant switch; ten of them were down regulated (proteins involved in glycolysis, TCA cycle, protein and lipid synthesis) while four others were overexpressed (mainly related to the cytoskeleton). These techniques are very reliable to describe the proteome from organisms such as insects in response to particular environmental change such as host plant species of herbivores.