Molecular approaches to increasing resistance of wheat (Triticum aestivum L.) towards two insect pests; Cereal aphid (Sitobion avenae F.) and Wheat bulb fly (Delia coarctata Fallen).

Cereal aphid (Sitobion avenae) and wheat bulb fly (Delia coarctata) are serious pests of wheat in the UK. At the present, chemical pesticides are used to control these insects, but they are limited in effectiveness, and have undersirable ecological impacts. There is a need to improve wheat genetically to be resistant to such inset pests. The objectives of this work were to investigate digestive biochemistry in the selected insect pests of wheat, and to determine effects of potential endogenous resistance factors in wheat on digestion, nutrition and other insect metabolic processes. The aim was to develop new strategies for crop protection. Digestive biochemistry in S. avenae and D. coarctata was studied to characterise gut proteases and their inhibition by host plant proteinase inhibitors (PIs). Investigation of proteolytic digestion in S. avenae gut showed that in spite of being a phloem-feeding insect, cereal aphid could digest ingested protein, using cysteine proteases. D. coarctata larvae contained mainly serine protease activity. A serine protease (DcSP) and a cysteine protease (DcCathL) from D. coarctata gut tissue were expressed as recombinant proteins. Only DcCathL was recovered in active form. DcCathL was insecticidal to Mamestra brassicae when injected into hemolymph, causing systemic and extensive melanisation. DcCathL selectively degraded recombinant serpins from M. brassicae in in vitro assays, and is suggested to interfere with regulation of the proteolytic cascade leading to phenoloxidase activation and melanin production in vivo. DcCathL has potential as a biopesticide if it could be made effective when orally delivered. A cationic amino acid transporter from D. coarctata gut (DcCAAT) was also cloned as a target for RNA interference. Potential resistance factors in wheat were characterised by expression as recombinant proteins. Two PIs from wheat (subtilisin/chymotrypsin inhibitor; WSCI, and cysteine proteinase inhibitor; WCPI) were expressed in the yeast Pichia pastoris, and purified. WSCI inhibited gut protease activity of both insects in in vitro and in vivo assays, whereas WCPI only inhibited S. avenae gut extract activity. On feeding, WSCI was antimetabolic to both insects, affecting both survival and growth, whereas WCPI was antimetabolic to S. avenae only. Wheat Hessian fly responsive (Hfr) genes are up-regulated in response to herbivory by Hessian fly (Mayetiola destructor). The protein product Hfr-3 was expressed and purified, and showed antimetabolic effects on survival and growth of both S. avenae and D. coarctata. Both accumulated and induced defence proteins, like WSCI, WCPI and Hfr-3, have the potential to act as endogenous resistance factors in wheat towards a range of insect pests. Developing a wheat variety constitutively expressing these defence proteins by using traditional breeding methods and/or modern biotechnological tools is discussed

Heterologous production of the insecticidal pea seed albumin PA1 protein by Pichia pastoris and protein engineering to potentiate aphicidal activity via fusion to snowdrop lectin Galanthus nivalis agglutinin; GNA)

BackgroundNew bioinsecticides with novel modes of action are urgently needed to minimise the environmental and safety hazards associated with the use of synthetic chemical pesticides and to combat growing levels of pesticide resistance. The pea seed albumin PA1b knottin peptide is the only known proteinaceous inhibitor of insect vacuolar adenosine triphosphatase (V-ATPase) rotary proton pumps. Oral toxicity towards insect pests and an absence of activity towards mammals makes Pa1b an attractive candidate for development as a bioinsecticide. The purpose of this study was to investigate if Pichia pastoris could be used to express a functional PA1b peptide and if it’s insecticidal activity could be enhanced via engineering to produce a fusion protein comprising the pea albumin protein fused to the mannose-specific snowdrop lectin (Galanthus nivalis agglutinin; GNA).ResultsWe report the production of a recombinant full-length pea albumin protein (designated PAF) and a fusion protein (PAF/GNA) comprised of PAF fused to the N-terminus of GNA in the yeast Pichia pastoris. PAF was orally toxic to pea (Acyrthosiphon pisum) and peach potato (Myzus persicae) aphids with respective, Day 5 LC50 values of 54 µM and 105 µM derived from dose–response assays. PAF/GNA was significantly more orally toxic as compared to PAF, with LC50 values tenfold (5 µM) and 3.3-fold (32 µM) lower for pea and peach potato aphids, respectively. By contrast, no phenotypic effects were observed for worker bumble bees (Bombus terristrus) fed PAF, GNA or PAF/GNA in acute toxicity assays. Confocal microscopy of pea aphid guts after pulse-chase feeding fluorescently labelled proteins provides evidence that enhanced efficacy of the fusion protein is attributable to localisation and retention of PAF/GNA to the gut epithelium. In contact assays the fusion protein was also found to be significantly more toxic towards A. pisum as compared to PAF, GNA or a combination of the two proteins.ConclusionsOur results suggest that GNA mediated binding to V-type ATPase pumps acts to potentiate the oral and contact aphicidal activity of PAF. This work highlights potential for the future commercial development of plant protein-based bioinsecticides that offer enhanced target specificity as compared to chemical pesticides, and compatibility with integrated pest management strategies

A recombinant fusion protein containing a spider toxin specific for the insect voltage-gated sodium ion channel shows oral toxicity towards insects of different orders

AbstractRecombinant fusion protein technology allows specific insecticidal protein and peptide toxins to display activity in orally-delivered biopesticides. The spider venom peptide δ-amaurobitoxin-PI1a, which targets insect voltage-gated sodium channels, was fused to the “carrier” snowdrop lectin (GNA) to confer oral toxicity.The toxin itself (PI1a) and an amaurobitoxin/GNA fusion protein (PI1a/GNA) were produced using the yeast Pichia pastoris as expression host. Although both proteins caused mortality when injected into cabbage moth (Mamestra brassicae) larvae, the PI1a/GNA fusion was approximately 6 times as effective as recombinant PI1a on a molar basis. PI1a alone was not orally active against cabbage moth larvae, but a single 30 μg dose of the PI1a/GNA fusion protein caused 100% larval mortality within 6 days when fed to 3rd instar larvae, and caused significant reductions in survival, growth and feeding in 4th – 6th instar larvae. Transport of fusion protein from gut contents to the haemolymph of cabbage moth larvae, and binding to the nerve chord, was shown by Western blotting. The PI1a/GNA fusion protein also caused mortality when delivered orally to dipteran (Musca domestica; housefly) and hemipteran (Acyrthosiphon pisum; pea aphid) insects, making it a promising candidate for development as a biopesticide

Insecticidal effects of dsRNA targeting the Diap1 gene in dipteran pests

The Drosophila melanogaster (fruit fly) gene Diap1 encodes a protein referred to as DIAP1 (DrosophilaInhibitor of Apoptosis Protein 1) that acts to supress apoptosis in “normal” cells in the fly. In this study we investigate the use of RNA interference (RNAi) to control two dipteran pests, Musca domestica and Delia radicum, by disrupting the control of apoptosis. Larval injections of 125–500 ng of Diap1 dsRNA resulted in dose-dependent mortality which was shown to be attributable to down-regulation of target mRNA. Insects injected with Diap1 dsRNA have approx. 1.5-2-fold higher levels of caspase activity than controls 24 hours post injection, providing biochemical evidence that inhibition of apoptotic activity by the Diap1 gene product has been decreased. By contrast adults were insensitive to injected dsRNA. Oral delivery failed to induce RNAi effects and we suggest this is attributable to degradation of ingested dsRNA by intra and extracellular RNAses. Non-target effects were demonstrated via mortality and down-regulation of Diap1 mRNA levels in M. domestica larvae injected with D. radicum Diap1 dsRNA, despite the absence of 21 bp identical sequence regions in the dsRNA. Here we show that identical 15 bp regions in dsRNA are sufficient to trigger non-target RNAi effects

Correction to: Transient expression of SbDhr2 and MeHNL in Gossypium hirsutum for herbivore deterrence assay with Spodoptera litura

An amendment to this paper has been published and can be accessed via the original article.</jats:p