Digestive proteolytic activity in the Sunn pest, Eurygaster integriceps

Abamectin exposure causes chronic toxicity and trypsin/chymotrypsin damages in Chironomus kiiensis Tokunaga (Diptera: Chironomidae)

Abamectin has been extensively used in paddy fields to control insect pests. However, little information is available regarding its effects on non-target insects. In this study, we performed acute (3rd instar larvae) and chronic toxicity (newly hatched larvae <24 h) to determine the toxicity effects of abamectin on Chironomus kiiensis. The median lethal concentration (LC50) values of 24 h and 10 d were 0.57 mg/L and 68.12 μg/L, respectively. The chronic exposure significantly prolonged the larvae growth duration and inhibited pupation and emergence. The transcriptome and biochemical parameters were measured using 3rd instar larvae exposed to acute LC10 and LC25 for 24 h. Transcriptome data indicated that five trypsin and four chymotrypsin genes were downregulated, and RT-qPCR verified a significant expression decrease in trypsin3 and chymotrypsin1 genes. Meanwhile, abamectin could significantly inhibit the activities of the serine proteases trypsin and chymotrypsin. RNA interference showed that silencing trypsin3 and chymotrypsin1 genes led to higher mortality of C. kiiensis to abamectin. In conclusion, these findings indicated that trypsin and chymotrypsin are involved in the abamectin toxicity against C. kiiensis, which provides new insights into the mechanism of abamectin-induced ecotoxicity to chironomids.

Screening of insect immune suppressors using a recombinant phospholipase A2 of a lepidopteran insect

Phospholipase A2 (PLA2 ) catalyzes phospholipids at the sn-2 position to release free fatty acids, including arachidonic acid (AA) or its precursor. The free AA is then oxygenated into different eicosanoids, which mediate the diverse physiological processes in insects. Any inhibition of the PLA2 catalysis would give rise to serious malfunctioning in insect growth and development. An onion moth, Acrolepiopsis sapporensis, encodes four different PLA2 genes (As-PLA2 A-As-PLA2 D), in which As-PLA2 A is dominantly expressed at all developmental stages and in different larval tissues. RNA interference of the As-PLA2 A expression significantly reduced the PLA2 activity of A. sapporensis, which suffered from immunosuppression. A recombinant As-PLA2 A protein was purified from a bacterial expression system, which exhibited a typical Michaelis-Menten kinetics and hence susceptible to a specific inhibitor to sPLA2 and dithiothreitol. A total of 19 bacterial metabolites derived from Xenorhabdus and Photorhabdus were screened against the recombinant As-PLA2 A. Five potent metabolites were highly inhibitory and followed a competitive enzyme inhibition. These five inhibitors suppressed the immune responses of A. sapporensis by inhibiting hemocyte-spreading behavior and phenoloxidase activity. However, an addition of AA could significantly rescue the immunosuppression induced by the selected inhibitors. These studies suggest that the recombinant As-PLA2 A protein can be applied for high-throughput screening of insect immunosuppressive compounds.

Soluble laticifer proteins from Calotropis procera as an effective candidates for antimicrobial therapeutics

Calotropis procera is a latex-producing plant with plenty of pharmacologically active compounds. The principal motivation behind this study was to separate and characterize laticifer proteins to check their antimicrobial potential. Laticifer proteins were separated by gel filtration chromatography (GFC) and investigated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The SDS-PAGE assay detected proteins of molecular weights of 10 to 30 kDa but most of them were in the range of 25 to 30 kDa. The soluble laticifer proteins (SLPs) were tested against Gram-positive bacteria i.e., Streptococcus pyogenes and Staphylococcus aureus whereas Escherichia coli and Pseudomonas aeruginosa were tested as Gram-negative bacteria, we determined a profound anti-bacterial activity of these proteins. In addition, SLPs were also investigated against Candida albicans via the agar disc diffusion method which also showed significant anti-fungal activity. SLP exhibited antibacterial activity against P. aeruginosa, E. coli, and S. aureus with a minimum inhibitory concentration (MIC) of 2.5 mg/mL for each, while MIC was found at 0.625 mg/mL for S. pyogenes and 1.25 mg/mL for C. albicans. Moreover, enzymatic activity evaluation of SLP showed the proteolytic nature of these proteins, and this proteolytic activity was greatly enhanced after reduction which might be due to the presence of cysteine residues in the protein structure. The activity of the SLPs obtained from the latex of C. procera can be associated with the involvement of enzymes either proteases or, protease inhibitors and/or peptides.

A prophylactic role of a secretory PLA2 of Spodoptera exigua against entomopathogens

Phospholipase A₂ (PLA₂) hydrolyses phospholipids at sn-2 position to release free fatty acids and lysophospholipids. Secretory type of PLA₂ (sPLA₂) has been found in many different animals including insects. Insect sPLA₂s have been divided into venomous and nonvenomous PLA₂s. A non-venomous sPLA₂ (Se-sPLA₂) has been identified in beet armyworm, Spodoptera exigua. Its high enzyme activity is detected in hemolymph of naïve larvae. However, the physiological role of high sPLA₂ activity in hemolymph remains unclear. To determine the physiological role of sPLA₂ in hemolymph, a recombinant Se-sPLA₂ (rSe-sPLA₂) was expressed in a bacterial expression system and purified to test antimicrobial activity against various microbes. Purified rSe-sPLA₂ exhibited typical enzyme kinetic properties, including becoming saturated at high substrate concentrations, exhibiting optimal activity at pH 7-9, and being inactivated at high temperatures. However, a reducing agent (dithiothreitol) or calcium chelator treatment inhibited the catalytic activity. A specific inhibitor to sPLA₂ also inhibited the enzyme activity of rSe-sPLA₂ while other type PLA₂ inhibitors did not. Furthermore, eight bacterial metabolites of Xenorhabdus and Photorhabdus known to be inhibitory against insect PLA₂ significantly inhibited the enzyme activity of rSe-sPLA₂. High concentrations of rSe-sPLA₂ (above 0.5 mM) showed significant cytotoxicity to hemocytes of S. exigua. At concentrations without showing cytotoxicity, rSe-sPLA₂ possessed significant antimicrobial activities against entomopathogenic bacteria (Serratia marscens and Entercoccus mondtii) and fungi (Beauveria bassiana and Metarhyzium rileyi). Hemolymph obtained from larvae treated with RNA interference specific to Se-sPLA₂ significantly lost such antimicrobial activities. However, the addition of rSe-sPLA₂ to the hemolymph significantly rescued such antimicrobial activities. These results indicate that Se-sPLA₂ possesses antimicrobial activity, suggesting that it might act as a prophylactic agent against microbial pathogens in the hemolymph of S. exigua.

Development of a NS2B/NS3 protease inhibition assay using AlphaScreen® beads for screening of anti-dengue activities

Background

Dengue infection is an endemic infectious disease and it can lead to dengue fever, dengue hemorrhagic fever, and/or dengue shock syndromes. Dengue NS2B/NS3 protease complex is essential for viral replication and is a primary target for anti-dengue drug development. In this study, a NS2B/NS3 protease inhibition assay was developed using AlphaScreen^® beads and was used to screen compounds for their protease inhibition activities.

Methods

The assay system utilized a known NS2B/NS3 peptide substrate, a recombinant of NS2B/NS3 protease with proprietary StrepTactin^® donor and nickel chelate acceptor beads in 384-well format.

Results

The optimized assay to screen for NS2B/NS3 protease inhibitors was demonstrated to be potentially useful with reasonable zʹ factor, coefficient variance and signal to background ratio. However, screening of synthesized thioguanine derivatives using the optimized AlphaScreen^® assay revealed weak NS2B/NS3 inhibition activities.

Conclusion

The AlphaScreen^® assay to screen for NS2B/NS3 protease inhibitors is potentially applicable for high throughput screening.

Development of a peptide substrate for detection of sunn pest damage in wheat flour

BACKGROUND

Since the common protease substrates did not give satisfactory results for the determination of Sunn pest protease activity in damaged wheat, different peptide substrates derived from the repeated sequences of high molecular weight glutenin subunits were synthesized.

RESULTS

Hydrolysis of peptides by pest protease was determined by high-performance liquid chromatography. Among three peptides having the same consensus motifs, peptide1 (PGQGQQGYYPTSPQQ) showed the best catalytic efficiency. A novel assay was described for monitoring the enzymatic activity of protease extracted from damaged wheat flour. The selected peptide was labeled with a fluorophore (EDANS) and quencher (Dabcyl) to display fluorescence resonance energy transfer. The proteolytic activity was measured by the change in fluorescence intensity that occurred when the protease cleaved the peptide substrate. Furthermore, the assay developed was modified for rapid and easy detection of bug damage in flour. Flour samples were suspended in water and mixed with fluorescence peptide substrate. After centrifugation, the fluorescence intensities of the supernatants, which are proportional to the protease content of the flour, were determined.

CONCLUSION

The total analysis time for the assay developed is estimated as 15 min. The assay developed permits a significant decrease in time and labor, offering sensitive detection of Sunn pest damage in wheat flour. © 2018 Society of Chemical Industry.

Role of inhibitors of serine peptidases in protecting Leishmania donovani against the hydrolytic peptidases of sand fly midgut

BACKGROUND

In vector-borne diseases such as leishmaniasis, the sand fly midgut is considered to be an important site for vector-parasite interaction. Digestive enzymes including serine peptidases such as trypsin and chymotrypsin, which are secreted in the midgut are one of the obstacles for Leishmania in establishing a successful infection. The presence of some natural inhibitors of serine peptidases (ISPs) has recently been reported in Leishmania. In the present study, we deciphered the role of these ISPs in the survival of Leishmania donovani in the hostile sand fly midgut environment.

METHODS

In silico and co-immunoprecipitation studies were performed to observe the interaction of L. donovani ISPs with trypsin and chymotrypsin. Zymography and in vitro enzyme assays were carried out to observe the inhibitory effect of purified recombinant ISPs of L. donovani (rLdISPs) on trypsin, chymotrypsin and the sand fly midgut peptidases. The expression of ISPs in the amastigote to promastigote transition stages were studied by semi-quantitative RT-PCR and Western blot. The role of LdISP on the survival of ISP overexpressed (OE) and ISP knocked down (KD) Leishmania parasites inside the sand fly gut was investigated by in vitro and in vivo cell viability assays.

RESULTS

We identified two ecotin-like genes in L. donovani, LdISP1 and LdISP2. In silico and co-immunoprecipitation results clearly suggest a strong interaction of LdISP molecules with trypsin and chymotrypsin. Zymography and in vitro enzyme assay confirmed the inhibitory effect of rLdISP on trypsin, chymotrypsin and the sand fly midgut peptidases. The expression of LdISP2 was found to be strongly associated with the amastigote to promastigote phase transition. The activities of the digestive enzymes were found to be significantly reduced in the infected sand flies when compared to uninfected. To our knowledge, our study is the first report showing the possible reduction of chymotrypsin activity in L. donovani infected sand flies compared to uninfected. Interestingly, during the early transition stage, substantial killing was observed in ISP2 knocked down (ISP2KD) parasites compared to wild type (WT), whereas ISP1 knocked down (ISP1KD) parasites remained viable. Therefore, our study clearly indicates that LdISP2 is a more effective inhibitor of serine peptidases than LdISP1.

CONCLUSION

Our results suggest that the lack of ISP2 is detrimental to the parasites during the early transition from amastigotes to promastigotes. Moreover, the results of the present study demonstrated for the first time that LdISP2 has an important role in the inhibition of peptidases and promoting L. donovani survival inside the Phlebotomus argentipes midgut.

Gene Duplication and Gene Expression Changes Play a Role in the Evolution of Candidate Pollen Feeding Genes in Heliconius Butterflies

Heliconius possess a unique ability among butterflies to feed on pollen. Pollen feeding significantly extends their lifespan, and is thought to have been important to the diversification of the genus. We used RNA sequencing to examine feeding-related gene expression in the mouthparts of four species of Heliconius and one nonpollen feeding species, Eueides isabella. We hypothesized that genes involved in morphology and protein metabolism might be upregulated in Heliconius because they have longer proboscides than Eueides, and because pollen contains more protein than nectar. Using de novo transcriptome assemblies, we tested these hypotheses by comparing gene expression in mouthparts against antennae and legs. We first looked for genes upregulated in mouthparts across all five species and discovered several hundred genes, many of which had functional annotations involving metabolism of proteins (cocoonase), lipids, and carbohydrates. We then looked specifically within Heliconius where we found eleven common upregulated genes with roles in morphology (CPR cuticle proteins), behavior (takeout-like), and metabolism (luciferase-like). Closer examination of these candidates revealed that cocoonase underwent several duplications along the lineage leading to heliconiine butterflies, including two Heliconius-specific duplications. Luciferase-like genes also underwent duplication within lepidopterans, and upregulation in Heliconius mouthparts. Reverse-transcription PCR confirmed that three cocoonases, a peptidase, and one luciferase-like gene are expressed in the proboscis with little to no expression in labial palps and salivary glands. Our results suggest pollen feeding, like other dietary specializations, was likely facilitated by adaptive expansions of preexisting genes—and that the butterfly proboscis is involved in digestive enzyme production.

Physiological responses of emerald ash borer larvae to feeding on different ash species reveal putative resistance mechanisms and insect counter-adaptations

Emerald ash borer, Agrilus planipennis Fairmaire, an Asian wood-boring beetle, has devastated ash (Fraxinus spp.) trees in North American forests and landscapes since its discovery there in 2002. In this study, we collected living larvae from EAB-resistant Manchurian ash (Fraxinus mandschurica), and susceptible white (Fraxinus americana) and green (Fraxinus pennsylvanica) ash hosts, and quantified the activity and production of selected detoxification, digestive, and antioxidant enzymes. We hypothesized that differences in larval physiology could be used to infer resistance mechanisms of ash. We found no differences in cytochrome P450, glutathione-S-transferase, carboxylesterase, sulfotransferase, and tryptic BApNAase activities between larvae feeding on different hosts. Despite this, Manchurian ash-fed larvae produced a single isozyme of low electrophoretic mobility that was not produced in white or green ash-fed larvae. Additionally, larvae feeding on white and green ash produced two serine protease isozymes of high electrophoretic mobility that were not observed in Manchurian ash-fed larvae. We also found lower activity of β-glucosidase and higher activities of monoamine oxidase, ortho-quinone reductase, catalase, superoxide dismutase, and glutathione reductase in Manchurian ash-fed larvae compared to larvae that had fed on susceptible ash. A single isozyme was detected for both catalase and superoxide dismutase in all larval groups. The activities of the quinone-protective and antioxidant enzymes are consistent with the resistance phenotype of the host species, with the highest activities measured in larvae feeding on resistant Manchurian ash. We conclude that larvae feeding on Manchurian ash could be under quinone and oxidative stress, suggesting these may be potential mechanisms of resistance of Manchurian ash to EAB larvae, and that quinone-protective and antioxidant enzymes are important counter-adaptations of larvae for dealing with these resistance mechanisms.

The Effect of Protease Inhibitors on Digestive Proteolytic Activity in the Raspberry Weevil, Aegorhinus superciliosus (Guérin) (Coleoptera: Curculionidae)

The raspberry weevil, Aegorhinus superciliosus (Guérin) (Coleoptera: Curculionidae), is an economically important pest of blueberry in southern Chile. The digestive protease activity of adult insects was investigated using general and specific substrates and inhibitors. Enzymatic assays demonstrated the presence of trypsin- and chymotrypsin-like serine proteinases. Furthermore, in vitro assays using phenylmethylsulfonyl fluoride (PMSF) and soybean trypsin inhibitor (SBTI) at 0.01 and 0.1 mM showed percentages of enzymatic inhibition between 0 and 16% for PMSF and 67 to 76% for SBTI, whereas in vivo assays indicated that SBTI caused between 50 and 90% mortality in males and between 80 and 100% in females. Our data indicate the presence of serine proteases and suggest that digestive proteases could be a target for the design and development of strategies to control the raspberry weevil.

Matrix expansion and syncytial aggregation of syndecan-1+ cells underpin villous atrophy in coeliac disease

Background

We studied the expression of sulphated glycosaminoglycans (GAGs) in coeliac disease (CD) mucosa, as they are critical determinants of tissue volume, which increases in active disease. We also examined mucosal expression of IL-6, which stimulates excess GAG synthesis in disorders such as Grave's ophthalmopathy.

Methods

We stained archival jejunal biopsies from 5 children with CD at diagnosis, on gluten-free diet and challenge for sulphated GAGs. We then examined duodenal biopsies from 9 children with CD compared to 9 histological normal controls, staining for sulphated GAGs, heparan sulphate proteoglycans (HSPG), short-chain HSPG (Δ-HSPG) and the proteoglycan syndecan-1 (CD138), which is expressed on epithelium and plasma cells. We confirmed findings with a second monoclonal in another 12 coeliac children. We determined mucosal IL-6 expression by immunohistochemistry and PCR in 9 further cases and controls, and used quantitative real time PCR for other Th17 pathway cytokines in an additional 10 cases and controls.

Results

In CD, HSPG expression was lost in the epithelial compartment but contrastingly maintained within an expanded lamina propria. Within the upper lamina propria, clusters of syndecan-1+ plasma cells formed extensive syncytial sheets, comprising adherent plasma cells, lysed cells with punctate cytoplasmic staining and shed syndecan ectodomains. A dense infiltrate of IL-6⁺ mononuclear cells was detected in active coeliac disease, also localised to the upper lamina propria, with significantly increased mRNA expression of IL-6 and IL-17A but not IL-23 p19.

Conclusions

Matrix expansion, through syndecan-1+ cell recruitment and lamina propria GAG increase, underpins villous atrophy in coeliac disease. The syndecan-1+ cell syncytia and excess GAG production recapitulate elements of the invertebrate encapsulation reaction, itself dependent on insect transglutaminase and glutaminated early response proteins. As in other matrix expansion disorders, IL-6 is upregulated and represents a logical target for immunotherapy in patients with coeliac disease refractory to gluten-free diet.

Salivary digestive enzymes of the wheat bug, Eurygaster integriceps (Insecta: Hemiptera: Scutelleridae)

The digestive enzymes from salivary gland complexes (SGC) of Eurygaster integriceps, and their response to starvation and feeding were studied. Moreover, digestive amylases were partially purified and characterized by ammonium sulfate precipitation and gel filtration chromatography. The SGC are composed of two sections, the principal glands and accessory glands. The principal glands are further divided into the anterior lobes and posterior lobes. The SGC main enzyme was α-amylase, which hydrolyzed starch better than glycogen. The other carbohydrases were also present in the SGC complexes. Enzymatic activities toward mannose (α/β-mannosidases) were little in comparison to activities against glucose (α/β-glucosidases) and galactose (α/β-galactosidases), the latter being the greatest. Acid phosphatase showed higher activity than alkaline phosphatase. There was no measurable activity for lipase and aminopeptidase. Proteolytic activity was detected against general and specific protease substrates. Activities of all enzymes were increased in response to feeding in comparison to starved insects, revealing their induction and secretion in response to feeding pulse. The SGC amylases eluted in four major peaks and post-electrophoretic detection of the α-amylases demonstrated the existence of at least five isoamylases in the SGC. The physiological implication of these findings in pre-oral digestion of E. integriceps is discussed.

Analysis of the salivary gland transcriptome of Frankliniella occidentalis

Saliva is known to play a crucial role in insect feeding behavior and virus transmission. Currently, little is known about the salivary glands and saliva of thrips, despite the fact that Frankliniella occidentalis (Pergande) (the western flower thrips) is a serious pest due to its destructive feeding, wide host range, and transmission of tospoviruses. As a first step towards characterizing thrips salivary gland functions, we sequenced the transcriptome of the primary salivary glands of F. occidentalis using short read sequencing (Illumina) technology. A de novo-assembled transcriptome revealed 31,392 high quality contigs with an average size of 605 bp. A total of 12,166 contigs had significant BLASTx or tBLASTx hits (E≤1.0E-6) to known proteins, whereas a high percentage (61.24%) of contigs had no apparent protein or nucleotide hits. Comparison of the F. occidentalis salivary gland transcriptome (sialotranscriptome) against a published F. occidentalis full body transcriptome assembled from Roche-454 reads revealed several contigs with putative annotations associated with salivary gland functions. KEGG pathway analysis of the sialotranscriptome revealed that the majority (18 out of the top 20 predicted KEGG pathways) of the salivary gland contig sequences match proteins involved in metabolism. We identified several genes likely to be involved in detoxification and inhibition of plant defense responses including aldehyde dehydrogenase, metalloprotease, glucose oxidase, glucose dehydrogenase, and regucalcin. We also identified several genes that may play a role in the extra-oral digestion of plant structural tissues including β-glucosidase and pectin lyase; and the extra-oral digestion of sugars, including α-amylase, maltase, sucrase, and α-glucosidase. This is the first analysis of a sialotranscriptome for any Thysanopteran species and it provides a foundational tool to further our understanding of how thrips interact with their plant hosts and the viruses they transmit.

Salivary proteins of plant-feeding hemipteroids - implication in phytophagy

Many hemipteroids are major pests and vectors of microbial pathogens, infecting crops. Saliva of the hemipteroids is critical in enabling them to be voracious feeders on plants, including the economically important ones. A plethora of hemipteroid salivary enzymes is known to inflict stress in plants, either by degrading the plant tissue or by affecting their normal metabolism. Hemipteroids utilize one of the following three strategies of feeding behaviour: salivary sheath feeding, osmotic-pump feeding and cell-rupture feeding. The last strategy also includes several different tactics such as lacerate-and-flush, lacerate-and-sip and macerate-and-flush. Understanding hemipteroid feeding mechanisms is critical, since feeding behaviour directs salivary composition. Saliva of the Heteroptera that are specialized as fruit and seed feeders, includes cell-degrading enzymes, auchenorrhynchan salivary composition also predominantly consists of cell-degrading enzymes such as amylase and protease, whereas that of the Sternorhyncha includes a variety of allelochemical-detoxifying enzymes. Little is known about the salivary composition of the Thysanoptera. Cell-degrading proteins such as amylase, pectinase, cellulase and pectinesterase enable stylet entry into the plant tissue. In contrast, enzymes such as glutathione peroxidase, laccase and trehalase detoxify plant chemicals, enabling the circumvention of plant-defence mechanisms. Salivary enzymes such as M1-zinc metalloprotease and CLIP-domain serine protease as in Acyrthosiphon pisum (Aphididae), and non-enzymatic proteins such as apolipophorin, ficolin-3-like protein and 'lava-lamp' protein as in Diuraphis noxia (Aphididae) have the capacity to alter host-plant-defence mechanisms. A majority of the hemipteroids feed on phloem, hence Ca++-binding proteins such as C002 protein, calreticulin-like isoform 1 and calmodulin (critical for preventing sieve-plate occlusion) are increasingly being recognized in hemipteroid-plant interactions. Determination of a staggering variety of proteins shows the complexity of hemipteroid saliva: effector proteins localized in hemipteran saliva suggest a similarity to the physiology of pathogen-plant interactions.

Identification and partial characterization of midgut proteases in the lesser mulberry pyralid, Glyphodes pyloalis

Proteolytic activities in digestive system extracts from the larval midgut of the lesser mulberry pyralid, Glyphodes pyloalis Walker (Lepidoptera: Pyralidae), were analyzed using different specific peptide substrates and proteinase inhibitors. High proteolytic activities were found at pH 10.0 and a temperature of 50° C using azocasein as substrate. The trypsin was active in the pH range of 9.5- 12.0, with its maximum activity at pH 11.5. Ethylene diamine tetraacetic acid had the most inhibitory effect, and 44% inhibition was detected in the presence of this inhibitor. Phenyl methane sulfonyl floride and N-tosyl-L-phe chloromethyl ketone also showed considerable inhibition of larval azocaseinolytic activity, with 40.2 and 35.1% inhibition respectively. These data suggest that the midgut of larvae contains mainly metalloproteases and serine proteases, mainly chymotrypsin. The effect of several metal ions on the activity of proteases showed that NaCl, CaCl2, CoCl2 (5 and 10 mM), and MnCl2 (5mM) reduced the protease activity. The kinetic parameters of trypsin-like proteases using N-benzoyl-L-arg-p-nitroanilide as substrate indicated that the Km and Vmax values of trypsin in the alimentary canal were 50.5 ± 2.0 µM and 116.06 ± 1.96 nmol min(-1) mg(-1) protein, respectively. Inhibition assays showed only small amounts of cysteine proteases were present in the G. pyloalis digestive system. The midgut digestive protease system of G. pyloalis is as diverse as that of any of the other polyphagous lepidopteran insect species, and the midgut of larvae contains mainly metalloproteases. Moreover, serine proteases and chymotrypsin also play main roles in protein digestion. Characterization of the proteolytic properties of the digestive enzymes of G. pyloalis offers an opportunity for developing appropriate and effective pest management strategies via metalloproteases and chymotrypsin inhibitors.

Transcriptome analysis of the salivary glands of potato leafhopper, Empoasca fabae

The potato leafhopper, Empoasca fabae, is a pest of economic crops in the United States and Canada, where it causes damage known as hopperburn. Saliva, along with mechanical injury, leads to decreases in gas exchange rates, stunting and chlorosis. Although E. fabae saliva is known to induce plant responses, little knowledge exists of saliva composition at the molecular level. We subjected the salivary glands of E. fabae to Roche 454-pyrosequencing which resulted significant number (30,893) of expressed sequence tags including 2805 contigs and 28,088 singletons. A high number of sequences (78%) showed similarity to other insect species in GenBank, including Triboliumcastaneum, Drosophilamelanogaster and Acrythosiphonpisum. KEGG analysis predicted the presence of pathways for purine and thiamine metabolic, biosynthesis of secondary metabolites, drug metabolism, and lysine degradation. Pfam analysis showed a high number of cellulase and carboxylesterase protein domains. Expression analysis of candidate genes (alpha amylase, lipase, pectin lyase, etc.) among different tissues revealed tissue-specific expression of digestive enzymes in E. fabae. This is the first study to characterize the sialotranscriptome of E. fabae and the first for any species in the family of Cicadellidae. Due to the status of these insects as economic pests, knowledge of which genes are active in the salivary glands is important for understanding their impact on host plants.

Characterization of cDNAs encoding serine proteases and their transcriptional responses to Cry1Ab protoxin in the gut of Ostrinia nubilalis larvae

Serine proteases, such as trypsin and chymotrypsin, are the primary digestive enzymes in lepidopteran larvae, and are also involved in Bacillus thuringiensis (Bt) protoxin activation and protoxin/toxin degradation. We isolated and sequenced 34 cDNAs putatively encoding trypsins, chymotrypsins and their homologs from the European corn borer (Ostrinia nubilalis) larval gut. Our analyses of the cDNA-deduced amino acid sequences indicated that 12 were putative trypsins, 12 were putative chymotrypsins, and the remaining 10 were trypsin and chymotrypsin homologs that lack one or more conserved residues of typical trypsins and chymotrypsins. Reverse transcription PCR analysis indicated that all genes were highly expressed in gut tissues, but one group of phylogenetically-related trypsin genes, OnTry-G2, was highly expressed in larval foregut and midgut, whereas another group, OnTry-G3, was highly expressed in the midgut and hindgut. Real-time quantitative PCR analysis indicated that several trypsin genes (OnTry5 and OnTry6) were significantly up-regulated in the gut of third-instar larvae after feeding on Cry1Ab protoxin from 2 to 24 h, whereas one trypsin (OnTry2) was down-regulated at all time points. Four chymotrypsin and chymotrypsin homolog genes (OnCTP2, OnCTP5, OnCTP12 and OnCTP13) were up-regulated at least 2-fold in the gut of the larvae after feeding on Cry1Ab protoxin for 24 h. Our data represent the first in-depth study of gut transcripts encoding expanded families of protease genes in O. nubilalis larvae and demonstrate differential expression of protease genes that may be related to Cry1Ab intoxication and/or resistance.

Insecticidal effect of labramin, a lectin-like protein isolated from seeds of the beach apricot tree, Labramia bojeri, on the Mediterranean flour moth, Ephestia kuehniella

The objective of this work was to study the insecticidal effect of labramin, a protein that shows lectin-like properties. Labramin was isolated from seeds of the Beach Apricot tree, Labramia bojeri A. DC ex Dubard (Ericales: Sapotaceae), and assessed against the development of the Mediterranean flour moth Ephestia kuehniella Zeller (Lepidoptera: Pyralidae), an important pest of stored products such as corn, wheat, rice, and flour. Results showed that labramin caused 90% larval mortality when incorporated in an artificial diet at a level of 1% (w/w). The presence of 0.25% labramin in the diet affected the larval and pupal developmental periods and the percentage of emerging adults. Treatments resulted in elevated levels of trypsin activity in midgut and fecal materials, indicating that labramin may have affected enzyme-regulatory mechanisms by perturbing peritrophic membranes in the midgut of is. kuehniella larvae. The results of dietary experiments with E. kuehniella larvae showed a reduced efficiency for the conversion of ingested and digested food, and an increase in approximate digestibility and metabolic cost. These findings suggest that labramin may hold promise as a control agent to engineer crop plants for insect resistance.

Influence of barley variety, timing of nitrogen fertilisation and sunn pest infestation on malting and brewing

BACKGROUND

This paper presents a multivariate approach to investigate the influence of barley variety, timing of nitrogen fertilisation and sunn pest infestation on malting and brewing. Four spring and two winter barley varieties were grown in one location in southern Europe. Moreover, one of the spring varieties was infested with sunn pest, in order to study the effects of this pest on malting quality, and subjected to different nitrogen fertilisation timing regimes. The samples were micromalted, mashed, brewed and analysed.

RESULTS

The data showed that even though the two winter barleys seemed to be the best regarding their physical appearance (sieving fraction I + II > 82%), this superiority was not confirmed in the malt samples, which showed low values of Hartong extract (27.1%) and high values of pH (6.07-6.11) and β-glucan content (12.5-13.2 g kg(-1)), resulting in low-quality beers. The barley sample subjected to postponed fertilisation had a total nitrogen content (19.5 g kg(-1) dry matter) exceeding the specification for malting barley and gave a beer with a low content of free amino nitrogen (47 mg L(-1)) and high values of viscosity (1.99 cP) and β-glucan content (533 mg L(-1)). The beer obtained from the barley sample subjected to pest attack had good quality parameters.

CONCLUSION

All spring barleys gave well-modified malts and consequently beers of higher quality than the winter barleys. Moreover, postponed fertilisation was negatively related to the quality of the final beer, and sunn pest infestation did not induce important economic losses in the beer production chain.

Characterization of a glutenin-specific serine proteinase of Sunn bug Eurygaster integricepts Put

Glutenin hydrolyzing proteinases (GHPs) have been purified, by affinity chromatography, from wheat seeds damaged by the Sunn bug Eurygaster integriceps (Hemiptera, Scutelleridae). A 28 kDa protein was partially sequenced by mass spectrometry and Edman degradation which showed homology to serine proteases from various insects. Three full length clones were obtained from cDNA isolated from Sunn bug salivary glands using degenerate PCR based on the sequences obtained. The cleavage site of the protease was determined using recombinant and synthetic peptides and shown to be between the consensus hexapeptide and nonapeptide repeat motifs present in the high molecular weight subunits of wheat glutenin (PGQGQQ∧GYYPTSLQQ). Homology models were generated for the three proteinases identified in this study using the high resolution X-ray structure of a crayfish (Pontastacus leptodactylus) trypsin complexed with a peptide inhibitor as template (PDB accession 2F91). The novel specificity of this protease may find applications in both fundamental and applied studies.

Effects of serine protease inhibitors on growth and development and digestive serine proteinases of the Sunn pest, Eurygaster integriceps

In the current study the effects of serine proteinase inhibitors (TLCK, TPCK, SBTI, and a combination of SBTI and TPCK) with concentrations of 1% and 4% of dietary protein in artificial diets were tested against growth of the Sunn pest, Eurygaster integriceps Puton (Hemiptera: Scutelleridae), development, and its gut serine proteinase targets. Analysis of variance indicated that protease inhibitors affected nymphal development time, adult weight, and survival. Mean development time of third instar nymphs in control, SBTI (1%), TLCK (1%), and TPCK was 7.18, 9.74, 9.97, and 8.52 days, respectively. The highest mortality (100 % mortality) was observed when a combination of TPCK and SBTI, both at 4% of dietary protein, was used followed by TPCK (4%) that produced 95% mortality. There were significant differences in proteinase activity between treatments and controls when BApNA and SAAPFpNA were used as substrates for trypsin and chymotrypsin, respectively. Reduction of trypsin activity in insects fed with low doses of SBTI (1%), TLCK (1%), and both doses of TPCK (1% and 4%) was 40, 26, 23, and 17%, respectively. Inhibition of chymotrypsin activity was seen in the insects fed on SBTI (1%), TLCK (1%), and TPCK (4%) where inhibition was 14, 9, and 36%, respectively. Maximum inhibition of chymotrypsin activity was observed in the insects fed on diets containing high doses of TPCK (4%). In gel assays, the greatest effects were observed when E. integriceps were fed on high doses of SBTI and TPCK. Therefore, TPCK followed by SBTI proved to be the most effective proteinase inhibitors of E. integriceps.