The Experts below are selected from a list of 4896 Experts worldwide ranked by ideXlab platform

Kenneth E Narva - One of the best experts on this subject based on the ideXlab platform.

  • Functional characterization of Vip3Ab1 and Vip3Bc1: Two novel Insecticidal Proteins with differential activity against lepidopteran pests
    Scientific Reports, 2017
    Co-Authors: Marc D. Zack, Sek Yee Tan, Megan S. Sopko, Meghan L. Frey, Xiujuan Wang, Jennifer M. Arruda, Ted T. Letherer, Kenneth E Narva
    Abstract:

    In this work, we characterized 2 novel Insecticidal Proteins; Vip3Ab1 and Vip3Bc1. These Proteins display unique Insecticidal spectra and have differential rates of processing by lepidopteran digestive enzymes. Furthermore, we have found that both Proteins exist as tetramers in their native state before and after proteolysis. In addition, we expressed truncated forms and protein chimeras to gain a deeper understanding of toxin specificity and stability. Our study confirms a role for the C-terminal 65 kDa domain in directing insect specificity. Importantly, these data also indicate a specific interaction between the 20 kDa amino terminus and 65 kDa carboxy terminus, after proteolytic processing. We demonstrate the C-terminal 65 kDa to be labile in native proteolytic conditions in absence of the 20 kDa N-terminus. Thus, the 20 kDa fragment functions to provide stability to the C-terminal domain, which is necessary for lethal toxicity against lepidopteran insects.

  • Histopathological Effects of Bt and TcdA Insecticidal Proteins on the Midgut Epithelium of Western Corn Rootworm Larvae (Diabrotica virgifera virgifera).
    Toxins, 2017
    Co-Authors: Andrew J. Bowling, Steven L. Evans, Sek Yee Tan, Heather E. Pence, Kenneth E Narva
    Abstract:

    Western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) is a major corn pest in the United States, causing annual losses of over $1 billion. One approach to protect against crop loss by this insect is the use of transgenic corn hybrids expressing one or more crystal (Cry) Proteins derived from Bacillus thuringiensis. Cry34Ab1 and Cry35Ab1 together comprise a binary Insecticidal toxin with specific activity against WCR. These Proteins have been developed as insect resistance traits in commercialized corn hybrids resistant to WCR feeding damage. Cry34/35Ab1 is a pore forming toxin, but the specific effects of Cry34/35Ab1 on WCR cells and tissues have not been well characterized microscopically, and the overall histopathology is poorly understood. Using high-resolution resin-based histopathology methods, the effects of Cry34/35Ab1 as well as Cry3Aa1, Cry6Aa1, and the Photorhabdus toxin complex protein TcdA have been directly visualized and documented. Clear symptoms of intoxication were observed for all Insecticidal Proteins tested, including swelling and sloughing of enterocytes, constriction of midgut circular muscles, stem cell activation, and obstruction of the midgut lumen. These data demonstrate the effects of these Insecticidal Proteins on WCR midgut cells, and the collective response of the midgut to intoxication. Taken together, these results advance our understanding of the insect cell biology and pathology of these Insecticidal Proteins, which should further the field of insect resistance traits and corn rootworm management.

  • rnai as a management tool for the western corn rootworm diabrotica virgifera virgifera
    Pest Management Science, 2016
    Co-Authors: Elane Fishilevich, Kenneth E Narva, Nicholas P Storer, Andrew J. Bowling, Ana Maria Velez, Murugesan Rangasamy, Sarah E Worden, Blair D Siegfried
    Abstract:

    The western corn rootworm (WCR), Diabrotica virgifera virgifera, is the most important pest of corn in the US Corn Belt. Economic estimates indicate that costs of control and yield loss associated with WCR damage exceed $US 1 billion annually. Historically, corn rootworm management has been extremely difficult because of its ability to evolve resistance to both chemical insecticides and cultural control practices. Since 2003, the only novel commercialized developments in rootworm management have been transgenic plants expressing Bt Insecticidal Proteins. Four transgenic Insecticidal Proteins are currently registered for rootworm management, and field resistance to Proteins from the Cry3 family highlights the importance of developing traits with new modes of action. One of the newest approaches for controlling rootworm pests involves RNA interference (RNAi). This review describes the current understanding of the RNAi mechanisms in WCR and the use of this technology for WCR management. Further, the review addresses ecological risk assessment of RNAi and insect resistance management of RNAi for corn rootworm. © 2016 Society of Chemical Industry.

  • bacillus thuringiensis cry34ab1 cry35ab1 interactions with western corn rootworm midgut membrane binding sites
    PLOS ONE, 2013
    Co-Authors: Monica Britt Olson, Gaofeng Lin, Timothy D Hey, Sek Yee Tan, Kenneth E Narva
    Abstract:

    Background Bacillus thuringiensis (Bt) Cry34Ab1/Cry35Ab1 are binary Insecticidal Proteins that are co-expressed in transgenic corn hybrids for control of western corn rootworm, Diabrotica virgifera virgifera LeConte. Bt crystal (Cry) Proteins with limited potential for field-relevant cross-resistance are used in combination, along with non-transgenic corn refuges, as a strategy to delay development of resistant rootworm populations. Differences in insect midgut membrane binding site interactions are one line of evidence that Bt protein mechanisms of action differ and that the probability of receptor-mediated cross-resistance is low.

  • transgenic approaches to western corn rootworm control
    Advances in Biochemical Engineering \ Biotechnology, 2013
    Co-Authors: Kenneth E Narva, Blair D Siegfried, Nicholas P Storer
    Abstract:

    The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) is a significant corn pest throughout the United States corn belt. Rootworm larvae feed on corn roots causing yield losses and control expenditures that are estimated to exceed US$1 billion annually. Traditional management practices to control rootworms such as chemical insecticides or crop rotation have suffered reduced effectiveness due to the development of physiological and behavioral resistance. Transgenic maize expressing Insecticidal Proteins are very successful in protecting against rootworm damage and preserving corn yield potential. However, the high rate of grower adoption and early reliance on hybrids expressing a single mode of action and low-dose traits threatens the durability of commercialized transgenic rootworm technology for rootworm control. A summary of current transgenic approaches for rootworm control and the corresponding insect resistance management practices is included. An overview of potential new modes of action based on Insecticidal Proteins, and especially RNAi targeting mRNA coding for essential insect Proteins is provided. Open image in new window Graphical Abstract

Juan Ferre - One of the best experts on this subject based on the ideXlab platform.

  • Mechanisms of Resistance to Insecticidal Proteins from Bacillus thuringiensis.
    Annual review of entomology, 2021
    Co-Authors: Juan Luis Jurat-fuentes, David G. Heckel, Juan Ferre
    Abstract:

    Insecticidal Proteins from the bacterium Bacillus thuringiensis (Bt) are used in sprayable formulations or produced in transgenic crops as the most successful alternatives to synthetic pesticides. The most relevant threat to sustainability of Bt Insecticidal Proteins (toxins) is the evolution of resistance in target pests. To date, high-level resistance to Bt sprays has been limited to one species in the field and another in commercial greenhouses. In contrast, there are currently seven lepidopteran and one coleopteran species that have evolved practical resistance to transgenic plants producing Insecticidal Bt Proteins. In this article, we present a review of the current knowledge on mechanisms of resistance to Bt toxins, with emphasis on key resistance genes and field-evolved resistance, to support improvement of Bt technology and its sustainability.

  • bacterial vegetative Insecticidal Proteins vip from entomopathogenic bacteria
    Microbiology and Molecular Biology Reviews, 2016
    Co-Authors: Maissa Chakroun, Nuria Banyuls, Yolanda Bel, Baltasar Escriche, Juan Ferre
    Abstract:

    Entomopathogenic bacteria produce Insecticidal Proteins that accumulate in inclusion bodies or parasporal crystals (such as the Cry and Cyt Proteins) as well as Insecticidal Proteins that are secreted into the culture medium. Among the latter are the Vip Proteins, which are divided into four families according to their amino acid identity. The Vip1 and Vip2 Proteins act as binary toxins and are toxic to some members of the Coleoptera and Hemiptera. The Vip1 component is thought to bind to receptors in the membrane of the insect midgut, and the Vip2 component enters the cell, where it displays its ADP-ribosyltransferase activity against actin, preventing microfilament formation. Vip3 has no sequence similarity to Vip1 or Vip2 and is toxic to a wide variety of members of the Lepidoptera. Its mode of action has been shown to resemble that of the Cry Proteins in terms of proteolytic activation, binding to the midgut epithelial membrane, and pore formation, although Vip3A Proteins do not share binding sites with Cry Proteins. The latter property makes them good candidates to be combined with Cry Proteins in transgenic plants (Bacillus thuringiensis-treated crops [Bt crops]) to prevent or delay insect resistance and to broaden the Insecticidal spectrum. There are commercially grown varieties of Bt cotton and Bt maize that express the Vip3Aa protein in combination with Cry Proteins. For the most recently reported Vip4 family, no target insects have been found yet.

  • binding site alteration is responsible for field isolated resistance to bacillus thuringiensis cry2a Insecticidal Proteins in two helicoverpa species
    PLOS ONE, 2010
    Co-Authors: Silvia Caccia, Carmen Sara Hernandezrodriguez, R J Mahon, Sharon Downes, William James, Nadine Bautsoens, Jeroen Van Rie, Juan Ferre
    Abstract:

    Background Evolution of resistance by target pests is the main threat to the long-term efficacy of crops expressing Bacillus thuringiensis (Bt) Insecticidal Proteins. Cry2 Proteins play a pivotal role in current Bt spray formulations and transgenic crops and they complement Cry1A Proteins because of their different mode of action. Their presence is critical in the control of those lepidopteran species, such as Helicoverpa spp., which are not highly susceptible to Cry1A Proteins. In Australia, a transgenic variety of cotton expressing Cry1Ac and Cry2Ab (Bollgard II) comprises at least 80% of the total cotton area. Prior to the widespread adoption of Bollgard II, the frequency of alleles conferring resistance to Cry2Ab in field populations of Helicoverpa armigera and Helicoverpa punctigera was significantly higher than anticipated. Colonies established from survivors of F2 screens against Cry2Ab are highly resistant to this toxin, but susceptible to Cry1Ac.

  • Insecticidal Genetically Modified Crops and Insect Resistance Management (IRM)
    Integration of Insect-Resistant Genetically Modified Crops within IPM Programs, 2008
    Co-Authors: Juan Ferre, Jeroen Van Rie, Susan C. Macintosh
    Abstract:

    Economically important crops, such as maize and cotton, have been transformed with genes encoding Insecticidal Proteins from Bacillus thuringiensis (Bt) to confer them protection against the most important insect pests. Of the 114 million hectares globally planted with GM crops in 2007, over one third are insect-resistant Bt crops, and the area keeps increasing every year. The potential for insects to evolve resistance to GM Insecticidal plants is considered to be one of the main threats to this technology, since resistance to Bt sprayable products has been demonstrated. Insect resistance management plans for this new class of pesticides are encouraged and became mandatory in the USA. Of the several strategies considered, a high dose of the Insecticidal protein along with an adjacent refuge plot of non-Bt plants has been chosen as the most effective. Second generation Bt cotton combines two Insecticidal Proteins with unique target sites. Such “pyramided” Bt crops hold great promise and, in combination with the high dose/refuge strategy, will likely confer maximum protection to the Bt crop technology against insect resistance. So far, no case of resistance evolution to Bt crops has been reported.

  • biochemistry and genetics of insect resistance to bacillus thuringiensis
    Annual Review of Entomology, 2002
    Co-Authors: Juan Ferre, Jeroen Van Rie
    Abstract:

    Bacillus thuringiensis (Bt) is a valuable source of Insecticidal Proteins for use in conventional sprayable formulations and in transgenic crops, and it is the most promising alternative to synthetic insecticides. However, evolution of resistance in insect populations is a serious threat to this technology. So far, only one insect species has evolved significant levels of resistance in the field, but laboratory selection experiments have shown the high potential of other species to evolve resistance against Bt. We have reviewed the current knowledge on the biochemical mechanisms and genetics of resistance to Bt products and Insecticidal crystal Proteins. The understanding of the biochemical and genetic basis of resistance to Bt can help design appropriate management tactics to delay or reduce the evolution of resistance in insect populations.

Leopoldo Palma - One of the best experts on this subject based on the ideXlab platform.

  • bacillus thuringiensis toxins an overview of their biocidal activity
    Toxins, 2014
    Co-Authors: Leopoldo Palma, Colin Berry, Delia Munoz, Jesus Murillo, Primitivo Caballero
    Abstract:

    Bacillus thuringiensis (Bt) is a Gram positive, spore-forming bacterium that synthesizes parasporal crystalline inclusions containing Cry and Cyt Proteins, some of which are toxic against a wide range of insect orders, nematodes and human-cancer cells. These toxins have been successfully used as bioinsecticides against caterpillars, beetles, and flies, including mosquitoes and blackflies. Bt also synthesizes Insecticidal Proteins during the vegetative growth phase, which are subsequently secreted into the growth medium. These Proteins are commonly known as vegetative Insecticidal Proteins (Vips) and hold Insecticidal activity against lepidopteran, coleopteran and some homopteran pests. A less well characterized secretory protein with no amino acid similarity to Vip Proteins has shown Insecticidal activity against coleopteran pests and is termed Sip (secreted Insecticidal protein). Bin-like and ETX_MTX2-family Proteins (Pfam PF03318), which share amino acid similarities with mosquitocidal binary (Bin) and Mtx2 toxins, respectively, from Lysinibacillus sphaericus, are also produced by some Bt strains. In addition, vast numbers of Bt isolates naturally present in the soil and the phylloplane also synthesize crystal Proteins whose biological activity is still unknown. In this review, we provide an updated overview of the known active Bt toxins to date and discuss their activities.

  • vip3c a novel class of vegetative Insecticidal Proteins from bacillus thuringiensis
    Applied and Environmental Microbiology, 2012
    Co-Authors: Carmen Sara Hernandezrodriguez, Baltasar Escriche, Leopoldo Palma, Delia Munoz, Mireya Maeztu, Patricia Hernandezmartinez, Inigo Ruiz De Escudero, Jeroen Van Rie
    Abstract:

    Three vip3 genes were identified in two Bacillus thuringiensis Spanish collections. Sequence analysis revealed a novel Vip3 protein class (Vip3C). Preliminary bioassays of larvae from 10 different lepidopteran species indicated that Vip3Ca3 caused more than 70% mortality in four species after 10 days at 4 μg/cm(2).

Blair D Siegfried - One of the best experts on this subject based on the ideXlab platform.

  • rnai as a management tool for the western corn rootworm diabrotica virgifera virgifera
    Pest Management Science, 2016
    Co-Authors: Elane Fishilevich, Kenneth E Narva, Nicholas P Storer, Andrew J. Bowling, Ana Maria Velez, Murugesan Rangasamy, Sarah E Worden, Blair D Siegfried
    Abstract:

    The western corn rootworm (WCR), Diabrotica virgifera virgifera, is the most important pest of corn in the US Corn Belt. Economic estimates indicate that costs of control and yield loss associated with WCR damage exceed $US 1 billion annually. Historically, corn rootworm management has been extremely difficult because of its ability to evolve resistance to both chemical insecticides and cultural control practices. Since 2003, the only novel commercialized developments in rootworm management have been transgenic plants expressing Bt Insecticidal Proteins. Four transgenic Insecticidal Proteins are currently registered for rootworm management, and field resistance to Proteins from the Cry3 family highlights the importance of developing traits with new modes of action. One of the newest approaches for controlling rootworm pests involves RNA interference (RNAi). This review describes the current understanding of the RNAi mechanisms in WCR and the use of this technology for WCR management. Further, the review addresses ecological risk assessment of RNAi and insect resistance management of RNAi for corn rootworm. © 2016 Society of Chemical Industry.

  • transgenic approaches to western corn rootworm control
    Advances in Biochemical Engineering \ Biotechnology, 2013
    Co-Authors: Kenneth E Narva, Blair D Siegfried, Nicholas P Storer
    Abstract:

    The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) is a significant corn pest throughout the United States corn belt. Rootworm larvae feed on corn roots causing yield losses and control expenditures that are estimated to exceed US$1 billion annually. Traditional management practices to control rootworms such as chemical insecticides or crop rotation have suffered reduced effectiveness due to the development of physiological and behavioral resistance. Transgenic maize expressing Insecticidal Proteins are very successful in protecting against rootworm damage and preserving corn yield potential. However, the high rate of grower adoption and early reliance on hybrids expressing a single mode of action and low-dose traits threatens the durability of commercialized transgenic rootworm technology for rootworm control. A summary of current transgenic approaches for rootworm control and the corresponding insect resistance management practices is included. An overview of potential new modes of action based on Insecticidal Proteins, and especially RNAi targeting mRNA coding for essential insect Proteins is provided. Open image in new window Graphical Abstract

Alejandra Bravo - One of the best experts on this subject based on the ideXlab platform.

  • specific binding between bacillus thuringiensis cry9aa and vip3aa toxins synergizes their toxicity against asiatic rice borer chilo suppressalis
    Journal of Biological Chemistry, 2018
    Co-Authors: Zeyu Wang, Fuping Song, Jie Zhang, Sabino Pacheco, Isabel Gómez, Mario Soberón, Longfa Fang, Zishan Zhou, Alejandra Bravo
    Abstract:

    : The bacterium Bacillus thuringiensis produces several Insecticidal Proteins, such as the crystal Proteins (Cry) and the vegetative Insecticidal Proteins (Vip). In this work, we report that a specific interaction between two B. thuringiensis toxins creates Insecticidal synergism and unravel the molecular basis of this interaction. When applied together, the three-domain Cry toxin Cry9Aa and the Vip Vip3Aa exhibited high Insecticidal activity against an important insect pest, the Asiatic rice borer (Chilo suppressalis). We found that these two Proteins bind specifically to brush border membrane vesicles of C. suppressalis and that they do not share binding sites because no binding competition was observed between them. Binding assays revealed that the Cry9Aa and Vip3Aa Proteins interacted with high affinity. We mapped their specific interacting regions by analyzing binding of Cry9Aa to overlapping fragments of Vip3Aa and by analyzing binding of Vip3Aa to individual domains of Cry9Aa. Binding to peptide arrays helped narrow the binding sites to domain II loop-3 of Cry9Aa and to 428TKKMKTL434 in Vip3Aa. Site-directed mutagenesis confirmed that these binding regions participate in binding that directly correlates with the synergism between the two Proteins. In summary, we show that the B. thuringiensis Cry9Aa and Vip3Aa toxins display potent synergy based on a specific interaction between them. Our results further our understanding of the complex synergistic activities among B. thuringiensis toxins and are highly relevant to the development of toxin combinations for effective insect control and for delaying development of insect resistance.

  • cry64ba and cry64ca two etx mtx2 type bacillus thuringiensis Insecticidal Proteins active against hemipteran pests
    Applied and Environmental Microbiology, 2017
    Co-Authors: Yonglei Liu, Fuping Song, Changlong Shu, Alejandra Bravo, Mario Soberón, Yinglong Wang, Kejian Lin, Jie Zhang
    Abstract:

    Genetically modified crops that express Insecticidal Bacillus thuringiensis (Bt) Proteins have become a primary approach for control of lepidopteran (moth) and coleopteran (beetle) pests that feed by chewing the plants. However, the sap-sucking insects (Hemiptera) are not particularly susceptible to Bt toxins. In this study, we describe two Cry toxins (Cry64Ba and Cry64Ca) from Bt strain 1012 that showed toxicity against two important hemipteran rice pests, Laodelphax striatellus and Sogatella furcifera Both of these Proteins contain an ETX/MTX2 domain and share common sequence features with the β-pore-forming toxins. Coexpression of cry64Ba and cry64Ca genes in the acrystalliferous Bt strain HD73- resulted in high Insecticidal activity against both hemipteran pests. No toxicity was observed on other pests such as Ostrinia furnacalis, Plutella xylostella, or Colaphellus bowringi Also, no hemolytic activity or toxicity against cancer cells was detected. Binding assays showed specific binding of the Cry64Ba/Cry64Ca toxin complex to brush border membrane vesicles isolated from L. striatellus Cry64Ba and Cry64Ca are Bt Cry toxins highly effective against hemipteran pests and could provide a novel strategy for the environmentally friendly biological control of rice planthoppers in transgenic plants.IMPORTANCE In Asia, rice is an important staple food, whose production is threatened by rice planthoppers. To date, no effective Bacillus thuringiensis (Bt) protein has been shown to have activity against rice planthoppers. We cloned two Bt toxin genes from Bt strain 1012 that showed toxicity against small brown planthoppers (Laodelphax striatellus) and white-backed planthoppers (Sogatella furcifera). To our knowledge, the Proteins encoded by the cry64Ba and cry64Ca genes are the most efficient Insecticidal Bt Cry Proteins with activity against hemipteran insects reported so far. Cry64Ba and Cry64Ca showed no toxicity against some lepidopteran or coleopteran pests. These two Proteins should be able to be used for integrated hemipteran pest management.

  • Insecticidal Proteins from Bacillus thuringiensis and Their Mechanism of Action
    Bacillus thuringiensis and Lysinibacillus sphaericus, 2017
    Co-Authors: Alejandra Bravo, Sabino Pacheco, Isabel Gómez, Blanca I. García-gómez, Janette Onofre, Mario Soberón
    Abstract:

    Bacillus thuringiensis (Bt) are Gram-positive bacteria that produce different Insecticidal Proteins, named Cry, Vip, and Cyt, during the sporulation phase of growth. Here we will describe each one of these classes of protein, their mechanism of action, and their three-dimensional structure if it is available. We will also describe the different strategies that have been used to find novel Insecticidal genes that could be used in biological control of insect pests as well as the strategies to evolve known genes to produce Proteins with improved toxicity against selected insect pests. These novel strategies include site-directed mutagenesis and domain swapping among different Cry toxins where novel hybrid Proteins containing domains or loop regions from different Cry Proteins were constructed, resulting in improved toxicity against selected insect pests. Finally we will describe high-throughput systems that have been used to evolve Cry toxins in vitro. Overall, Bt toxins represent one of the most successful strategies for the biocontrol of insect pests.

  • single concentration tests show synergism among bacillus thuringiensis subsp israelensis toxins against the malaria vector mosquito anopheles albimanus
    Journal of Invertebrate Pathology, 2010
    Co-Authors: Maria Teresa Fernandezluna, Alejandra Bravo, Mario Soberón, Bruce E Tabashnik, Humberto Lanzmendoza, Juan Mirandarios
    Abstract:

    Abstract Bioassays of Insecticidal Proteins from Bacillus thuringiensis subsp. israelensis with larvae of the malaria vector mosquito Anopheles albimanus showed that the cytolytic protein Cyt1Aa was not toxic alone, but it increased the toxicity of the crystalline Proteins Cry4Ba and Cry11Aa. Synergism also occurred between Cry4Ba and Cry11Aa toxins. Whereas many previous analyses of synergism have been based on a series of toxin concentrations leading to comparisons between expected and observed values for the concentration killing 50% of insects tested (LC50), we describe and apply a method here that enables testing for synergism based on single concentrations of toxins.