Wheat damage by Aelia spp. and Erygaster spp.: effects on gluten and water-soluble compounds released by gluten hydrolysis

Topographical Based Significance of Sap-Sucking Heteropteran in European Wheat Cultivations: A Systematic Review

Sap sucking heteropteran cereal bugs—members of the Eurygaster and Aelia genus—are serious pests of wheat. Moreover, they feed on a variety of gramineous plant species, including rye, barley, oat, maize, and millet. They are widely distributed in the European continent. The purpose of this review paper is two-fold; it summarizes the currently available data on the biological characteristics, the inflicted damage, and their European distribution and, in addition, we aimed to determine their economic importance, based on data available in the current literature. For the most important cereal bug species, we have collected data on their occurrence in Europe to provide a comprehensive picture of their distribution, and characterized them according to their temperature requirements at different life stages. We have also determined the degree of their attachment to wheat as their host plant, examining the synchronization between the pests and the life cycle of the plant. Finally, we compared their migration characteristics. All the above-mentioned characteristics were merged, in order to assess and rank the damage potential of each species.

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.

MOLECULAR IDENTIFICATION OF CYSTEINE AND TRYPSIN PROTEASE, EFFECT OF DIFFERENT HOSTS ON PROTEASE EXPRESSION, AND RNAI MEDIATED SILENCING OF CYSTEINE PROTEASE GENE IN THE SUNN PEST

Sunn pest, Eurygaster integriceps, is a serious pest of cereals in the wide area of the globe from Near and Middle East to East and South Europe and North Africa. This study described for the first time, identification of E. integriceps trypsin serine protease and cathepsin-L cysteine, transcripts involved in digestion, which might serve as targets for pest control management. A total of 478 and 500 base pair long putative trypsin and cysteine gene sequences were characterized and named Tryp and Cys, respectively. In addition, the tissue-specific relative gene expression levels of these genes as well as gluten hydrolase (Gl) were determined under different host kernels feeding conditions. Result showed that mRNA expression of Cys, Tryp, and Gl was significantly affected after feeding on various host plant species. Transcript levels of these genes were most abundant in the wheat-fed E. integriceps larvae compared to other hosts. The Cys transcript was detected exclusively in the gut, whereas the Gl and Tryp transcripts were detectable in both salivary glands and gut. Also possibility of Sunn pest gene silencing was studied by topical application of cysteine double-stranded RNA (dsRNA). The results indicated that topically applied dsRNA on fifth nymphal stage can penetrate the cuticle of the insect and induce RNA interference. The Cys gene mRNA transcript in the gut was reduced to 83.8% 2 days posttreatment. Also, it was found that dsRNA of Cys gene affected fifth nymphal stage development suggesting the involvement of this protease in the insect growth, development, and molting.

Effects of wheat bug (Eurygaster spp. and Aelia spp.) infestation in preharvest period on wheat technological quality and gluten composition

The effects of wheat bug infestation (Eurygaster spp. and Aelia spp.) on the composition of wheat gluten proteins and its influence on flour technological quality were investigated in the present study. Wheat samples of six wheat varieties, collected from two localities in northern Serbia, were characterized by significantly different level of wheat bug infestation. Composition of wheat gluten proteins was determined using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE), while the selected parameters of technological quality were determined according to standard and modified empirical rheological methods (Farinograph, Extensograph, Alveograph, and Gluten Index). The surface morphology of the selected samples was viewed using scanning electron microscopy (SEM). Wheat from wheat bug-infested locality regardless of the variety had deteriorated technological quality expressed with higher Farinograph softening degree, lower or immeasurable Extensograph energy, and Alveograph deformation energy. The most important changes in the gluten proteins composition of bug-infested wheat were related to gliadin subunits with molecular weights below 75 kDa, which consequently caused deterioration of uniaxial and biaxial extensibility and dough softening during mixing.

Population density and distribution of wheat bugs infesting durum wheat in Sardinia, Italy

Wheat is a very important crop in Italy, and is infested by wheat bugs belonging to the genera Eurygaster (Hemiptera: Scutellaridae) and Aelia (Hemiptera: Pentatomidae). Many wheat bug infestations have been reported in the north, south, and center of Italy, both in the past as well as recently. The present study was carried out in Sardinia, Italy, during two years (2007 and 2008). The objective of this study was to determine the species and distribution of wheat bugs in durum wheat fields in Sardinia, and to estimate their population density in order to know the incidence of the pest on the island. Sampling took place twice a year (May and June) in three zones, representative of durum wheat cropping in the island. Four species of wheat bugs were found; the predominant species was Eurygaster austriaca (Schrank), followed by Aelia germari (Kuster), Eurygaster maura L., and Aelia acuminata L. The average density of wheat bugs was low (1.1 individuals/m²), but in certain areas it was above the damage threshold (4 individuals/m²). For this reason, the conclusion of the study is that this pest should be monitored in order to control outbreaks and prevent their further spread.

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.

Digestive proteolytic activity in the Sunn pest, Eurygaster integriceps

The Sunn pest, Eurygaster integriceps Puton (Heteroptera: Scutelleridae), is one of the most important pests of wheat and causes considerable damage to this valuable crop annually. Digestive proteinase activity of adult insects was investigated using general and specific substrates and inhibitors. Proteolytic activity was low when the common conventional substrates, azoalbumin, azocasein and hemoglobin were used to assay salivary glands and midguts. Using the fluorescent casein substrate (BODIPY FL casein), total proteolytic activity was measured at different pH. Maximum proteolytic activity was detected at pH 7 (100%) and 8(65%) which suggested the presence of serine proteinases in the salivary glands. There was no detectable proteolytic activity in midgut extracts. The inhibitors; PMSF (inhibitor of serine proteinases) and TPCK (a specific chymotrypsin inhibitor) showed greater than 50% inhibitory effect on total proteolytic activity, however, TLCK (specific trypsin inhibitor) and E-64(specific cysteine proteinase inhibitor) did not inhibit total proteolytic activity. Using fluorescent specific substrates for serine and cysteine proteinases (Z-Arg-AMC, Z-Arg-Arg-AMC, Z-Arg-Phe-AMC and Suc-Ala-Ala-Pro-Phe-AMZ) revealed the presence of tryptic and chymotryptic activity in the salivary gland extract. Zymogram analysis under non-reducing SDS-PAGE conditions and using the substrate APNE showed at least 8 tryptic and chymotryptic activity bands in salivary gland extracts. A single high molecular weight band with tryptic activity (165 kDa) was detected using the substrate BApNA in a zymogram analysis using native-PAGE. Kinetic studies showed a k(m) value of 0.6 mM for this enzyme against the substrate BApNA .The inhibitor TLCK decreased activity of the trypsin-like enzyme up to 73% and almost completely eliminated the only band related to this proteinase in the zymogram. Soybean Kunitz type trypsin inhibitor showed no effect on proteolytic activity of the trypsin-like serine proteinase. In general, the results revealed the presence of chymotrypsin- and trypsin-like serine proteinases in the salivary gland of E. integriceps, and it seems that the major total proteolytic activity is due to chymotrypsin proteinases.