Toxins

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12 pages, 1989 KiB

Open AccessFeature PaperArticle

Binding and Synergizing Motif within Coleopteran Cadherin Enhances Cry3Bb Toxicity on the Colorado Potato Beetle and the Lesser Mealworm

by Youngjin Park, Gang Hua, Suresh Ambati, Milton Taylor and Michael J. Adang

Toxins 2019, 11(7), 386; https://doi.org/10.3390/toxins11070386 - 02 Jul 2019

Cited by 7 | Viewed by 2841

Abstract

Cry3Bb toxin from Bacillus thuringiensis is an important insecticidal protein due to its potency against coleopteran pests, especially rootworms. Cadherin, a protein in the insect midgut epithelium, is a receptor of Cry toxins; in some insect species toxin-binding domains of cadherins-synergized Cry toxicity. [...] Read more.

Cry3Bb toxin from Bacillus thuringiensis is an important insecticidal protein due to its potency against coleopteran pests, especially rootworms. Cadherin, a protein in the insect midgut epithelium, is a receptor of Cry toxins; in some insect species toxin-binding domains of cadherins-synergized Cry toxicity. Previously, we reported that the DvCad1-CR8-10 fragment of Diabrotica virgifera virgifera cadherin-like protein (GenBank Accession #EF531715) enhanced Cry3Bb toxicity to the Colorado Potato Beetle (CPB), Leptinotarsa decimlineata (L. decimlineata). We report that individual CR domains of the DvCad1-CR8-10 fragment were found to have strong binding affinities to α-chymotrypsin-treated Cry3Bb. The dissociation constant (K_d) of Cry3Bb binding to the CR8, CR9, and CR10 domain was 4.9 nM, 28.2 nM, and 4.6 nM, respectively. CR8 and CR10, but not CR9, enhanced Cry3Bb toxicity against L. decimlineata and the lesser mealworm Alphitobius diaperinus neonates. In-frame deletions of the DvCad1-CR10 open reading frame defined a high-affinity binding and synergistic site to a motif in residues I1226–D1278. A 26 amino acid peptide from the high affinity Cry3Bb-binding region of CR10 functioned as a Cry3Bb synergist against coleopteran larvae. Full article

(This article belongs to the Special Issue Insecticidal Toxins: Advances in Discovery and PestControl Applications)

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25 pages, 5336 KiB

Open AccessEditor’s ChoiceArticle

Identification and Evaluations of Novel Insecticidal Proteins from Plants of the Class Polypodiopsida for Crop Protection against Key Lepidopteran Pests

by Lu Liu, Eric Schepers, Amy Lum, Janet Rice, Nasser Yalpani, Ryan Gerber, Nuria Jiménez-Juárez, Fikru Haile, Alejandra Pascual, Jennifer Barry, Xiuli Qi, Adane Kassa, Matthew J. Heckert, Weiping Xie, Changkui Ding, Jarred Oral, Minh Nguyen, James Le, Lisa Procyk, Scott H. Diehn, Virginia C. Crane, Howard Damude, Carol Pilcher, Russ Booth, Lu Liu, Genhai Zhu, Timothy M. Nowatzki, Mark E. Nelson, Albert L. Lu and Gusui Wu Show full author list Hide full author list

Toxins 2019, 11(7), 383; https://doi.org/10.3390/toxins11070383 - 01 Jul 2019

Cited by 17 | Viewed by 8494

Abstract

Various lepidopteran insects are responsible for major crop losses worldwide. Although crop plant varieties developed to express Bacillus thuringiensis (Bt) proteins are effective at controlling damage from key lepidopteran pests, some insect populations have evolved to be insensitive to certain Bt proteins. Here, [...] Read more.

Various lepidopteran insects are responsible for major crop losses worldwide. Although crop plant varieties developed to express Bacillus thuringiensis (Bt) proteins are effective at controlling damage from key lepidopteran pests, some insect populations have evolved to be insensitive to certain Bt proteins. Here, we report the discovery of a family of homologous proteins, two of which we have designated IPD083Aa and IPD083Cb, which are from Adiantum spp. Both proteins share no known peptide domains, sequence motifs, or signatures with other proteins. Transgenic soybean or corn plants expressing either IPD083Aa or IPD083Cb, respectively, show protection from feeding damage by several key pests under field conditions. The results from comparative studies with major Bt proteins currently deployed in transgenic crops indicate that the IPD083 proteins function by binding to different target sites. These results indicate that IPD083Aa and IPD083Cb can serve as alternatives to traditional Bt-based insect control traits with potential to counter insect resistance to Bt proteins. Full article

(This article belongs to the Special Issue Insecticidal Toxins: Advances in Discovery and PestControl Applications)

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10 pages, 662 KiB

Open AccessEditor’s ChoiceArticle

Structural Domains of the Bacillus thuringiensis Vip3Af Protein Unraveled by Tryptic Digestion of Alanine Mutants

by Yudong Quan and Juan Ferré

Toxins 2019, 11(6), 368; https://doi.org/10.3390/toxins11060368 - 21 Jun 2019

Cited by 19 | Viewed by 3199

Abstract

Vip3 proteins are increasingly used in insect control in transgenic crops. To shed light on the structure of these proteins, we used the approach of the trypsin fragmentation of mutants altering the conformation of the Vip3Af protein. From an alanine scanning of Vip3Af, [...] Read more.

Vip3 proteins are increasingly used in insect control in transgenic crops. To shed light on the structure of these proteins, we used the approach of the trypsin fragmentation of mutants altering the conformation of the Vip3Af protein. From an alanine scanning of Vip3Af, we selected mutants with an altered proteolytic pattern. Based on protease digestion patterns, their effect on oligomer formation, and theoretical cleavage sites, we generated a map of the Vip3Af protein with five domains which match some of the domains proposed independently by two in silico models. Domain I ranges amino acids (aa) 12–198, domain II aa199–313, domain III aa314–526, domain IV aa527–668, and domain V aa669–788. The effect of some mutations on the ability to form a tetrameric molecule revealed that domains I–II are required for tetramerization, while domain V is not. The involvement of domain IV in the tetramer formation is not clear. Some mutations distributed from near the end of domain I up to the end of domain II affect the stability of the first three domains of the protein and destroy the tetrameric form upon trypsin treatment. Because of the high sequence similarity among Vip3 proteins, we propose that our domain map can be extended to the Vip3 family of proteins. Full article

(This article belongs to the Special Issue Insecticidal Toxins: Advances in Discovery and PestControl Applications)

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14 pages, 2396 KiB

Open AccessArticle

Modification of Vip3Ab1 C-Terminus Confers Broadened Plant Protection from Lepidopteran Pests

by Megan S. Sopko, Kenneth E. Narva, Andrew J. Bowling, Heather E. Pence, James J. Hasler, Theodore J. Letherer, Cory M. Larsen and Marc D. Zack

Toxins 2019, 11(6), 316; https://doi.org/10.3390/toxins11060316 - 03 Jun 2019

Cited by 5 | Viewed by 2631

Abstract

Vegetative insecticidal proteins (Vips) from Bacillus thuringiensis (Bt) are unique from crystal (Cry) proteins found in Bt parasporal inclusions as they are secreted during the bacterial vegetative growth phase and bind unique receptors to exert their insecticidal effects. We previously demonstrated that large [...] Read more.

Vegetative insecticidal proteins (Vips) from Bacillus thuringiensis (Bt) are unique from crystal (Cry) proteins found in Bt parasporal inclusions as they are secreted during the bacterial vegetative growth phase and bind unique receptors to exert their insecticidal effects. We previously demonstrated that large modifications of the Vip3 C-terminus could redirect insecticidal spectrum but results in an unstable protein with no lethal activity. In the present work, we have generated a new Vip3 protein, Vip3Ab1-740, via modest modification of the Vip3Ab1 C-terminus. Vip3Ab1-740 is readily processed by midgut fluid enzymes and has lethal activity towards Spodoptera eridania, which is not observed with the Vip3Ab1 parent protein. Importantly, Vip3Ab1-740 does retain the lethal activity of Vip3Ab1 against other important lepidopteran pests. Furthermore, transgenic plants expressing Vip3Ab1-740 are protected against S. eridania, Spodoptera frugiperda, Helicoverpa zea, and Pseudoplusia includens. Thus, these studies demonstrate successful engineering of Vip3 proteins at the C-terminus to broaden insecticidal spectrum, which can be employed for functional expression in planta. Full article

(This article belongs to the Special Issue Insecticidal Toxins: Advances in Discovery and PestControl Applications)

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17 pages, 2995 KiB

Open AccessArticle

Insecticidal Activity of a Vip3Ab1 Chimera Is Conferred by Improved Protein Stability in the Midgut of Spodoptera eridania

by Andrew J. Bowling, Megan S. Sopko, Sek Yee Tan, Cory M. Larsen, Heather E. Pence and Marc D. Zack

Toxins 2019, 11(5), 276; https://doi.org/10.3390/toxins11050276 - 16 May 2019

Cited by 4 | Viewed by 2815

Abstract

Vip3A proteins are important for the control of spodopteran pests in crops, including Spodoptera frugiperda (fall armyworm). Native Vip3Ab1 controls S. frugiperda, but it is ineffective against S. eridania (southern armyworm), a major pest of soybean in South America. Recently, a Vip3Ab1 [...] Read more.

Vip3A proteins are important for the control of spodopteran pests in crops, including Spodoptera frugiperda (fall armyworm). Native Vip3Ab1 controls S. frugiperda, but it is ineffective against S. eridania (southern armyworm), a major pest of soybean in South America. Recently, a Vip3Ab1 chimera with a modified C-terminus was described, Vip3Ab1-740, which has increased potency against S. eridania while maintaining activity against S. frugiperda. As S. frugiperda and S. eridania are differentially susceptible to Vip3Ab1, experiments were conducted to identify and understand the mechanism by which this expanded potency is conferred. The role of protein stability, processing, and in vivo effects of Vip3Ab1 and Vip3Ab1-740 in both of these species was investigated. Biochemical characterization of the midgut fluids of these two species indicated no obvious differences in the composition and activity of digestive enzymes, which protease inhibitor studies indicated were likely serine proteases. Histological examination demonstrated that both proteins cause midgut disruption in S. frugiperda, while only Vip3Ab1-740 affects S. eridania. Immunolocalization indicated that both proteins were present in the midgut of S. frugiperda, but only Vip3Ab1-740 was detected in the midgut of S. eridania. We conclude that the gain of toxicity of Vip3Ab1-740 to S. eridania is due to an increase in protein stability in the midgut, which was conferred by C-terminal modification. Full article

(This article belongs to the Special Issue Insecticidal Toxins: Advances in Discovery and PestControl Applications)

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20 pages, 2024 KiB

Open AccessArticle

Interactive Effects of [CO₂] and Temperature on Plant Chemistry of Transgenic Bt Rice and Population Dynamics of a Non-Target Planthopper, Nilaparvata lugens (Stål) under Different Levels of Soil Nitrogen

by Yanmin Liu, Zhihao Dang, Yanhui Wang, Megha N. Parajulee and Fajun Chen

Toxins 2019, 11(5), 261; https://doi.org/10.3390/toxins11050261 - 08 May 2019

Cited by 7 | Viewed by 2756

Abstract

Gaining a better understanding of the interactive effect of projected atmospheric CO₂ level increase and the Earth’s rising temperature on plant chemistry (nutritional and defensive characteristics) of transgenic crops is essential when attempting to forecast the responses of target and non-target insects [...] Read more.

Gaining a better understanding of the interactive effect of projected atmospheric CO₂ level increase and the Earth’s rising temperature on plant chemistry (nutritional and defensive characteristics) of transgenic crops is essential when attempting to forecast the responses of target and non-target insects to climate change. In this study, effects of carbon dioxide (CO₂; elevated versus ambient), temperature (T; high versus low), and their interactions on leaf nitrogen content (N%) and C:N ratio of transgenic Bt rice and its non-Bt isoline grown under low- and high-N fertilizer were systematically analyzed together with the resulting insect population dynamics of a non-target planthopper Nilaparvata lugens (Stâl) in open-top-chamber experiments. The results indicated that under low-N treatment, elevated CO₂ at low T (i.e., eCO₂) (compared to ambient CO₂ at low T, i.e., CK) significantly decreased N% and Bt-toxin content and significantly increased C:N ratio in leaf sheath and leaf of Bt rice, especially during the tillering stage, whereas inverse effects of high T were shown on the plant chemistry of Bt rice, especially during heading stage. The combination of elevated CO₂ and high T (i.e., Combined) (in contrast to CK) significantly increased N% and decreased C:N ratio in leaf sheath of Bt rice during the heading stage under low-N fertilizer, while significantly decreased N% and increased C:N ratio in leaf of Bt rice during the tillering stage, regardless of fertilizer-N level, and significantly increased Bt-toxin content in leaf sheath and leaf during the tillering stage under both low- and high-N. Moreover, no discernable relationships between Bt-toxin content and N% or leaf C:N ratio were observed at any CO₂ or N levels evaluated. Furthermore, transgenic treatment, temperature and fertilizer-N level interactions, and CO₂ and fertilizer-N level interactions all significantly affected the population dynamics of N. lugens. Specifically, high-N significantly enhanced the population dynamics of N. lugens fed on non-Bt rice grown under eTemp and Bt cultivar significantly reduced the population dynamics of N. lugens under eCO₂ regardless of N fertilizer levels. The study demonstrates that the planting of transgenic Bt rice would not increase the risk of increased N. lugens severity under the combined condition of elevated CO₂ and increased temperature, particularly under moderate level of N fertility. Full article

(This article belongs to the Special Issue Insecticidal Toxins: Advances in Discovery and PestControl Applications)

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13 pages, 1695 KiB

Open AccessArticle

Toxicity of Bacillus thuringiensis-Derived Pesticidal Proteins Cry1Ab and Cry1Ba against Asian Citrus Psyllid, Diaphorina citri (Hemiptera)

by Maria Teresa Fernandez-Luna, Pavan Kumar, David G. Hall, Ashaki D. Mitchell, Michael B. Blackburn and Bryony C. Bonning

Toxins 2019, 11(3), 173; https://doi.org/10.3390/toxins11030173 - 22 Mar 2019

Cited by 17 | Viewed by 4752

Abstract

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera), is an important pest of citriculture. The ACP vectors a bacterium that causes huanglongbing (HLB), a devastating and incurable disease of citrus. The bacterium Bacillus thuringiensis (Bt) produces multiple toxins with activity against a [...] Read more.

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera), is an important pest of citriculture. The ACP vectors a bacterium that causes huanglongbing (HLB), a devastating and incurable disease of citrus. The bacterium Bacillus thuringiensis (Bt) produces multiple toxins with activity against a diverse range of insects. In efforts to provide additional control methods for the ACP vector of HLB, we identified pesticidal proteins derived from Bt for toxicity against ACP. The trypsin proteolytic profiles of strain-derived toxins were characterized. Strain IBL-00200, one of six strains with toxins shown to have basal activity against ACP was selected for liquid chromatography-mass spectrometry (LC-MS/MS) identification of the individual Cry toxins expressed. Toxicity assays with individual toxins derived from IBL-00200 were then performed. The activated form of the Cry toxins Cry1Ab and Cry1Ba were toxic to ACP with LC₅₀ values of approximately 120 µg/mL. Disruption of the midgut epithelium was associated with the toxicity of both the IBL-00200-derived toxin mixture, and with Cry1Ba. With further optimization of the efficacy of Cry1Ab and Cry1Ba, these toxins may have practical utility against ACP. Bt toxins with activity against ACP may provide an additional tool for management of ACP and the associated HLB disease, thereby providing a more sustainable and environmentally benign approach than repeated application of broad-spectrum insecticides. Full article

(This article belongs to the Special Issue Insecticidal Toxins: Advances in Discovery and PestControl Applications)

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13 pages, 1997 KiB

Open AccessArticle

Granulovirus GP37 Facilitated ODVs Cross Insect Peritrophic Membranes and Fuse with Epithelia

by Xiangyang Liu, Wei Fang, Rui Fan, Linna Zhang, Chengfeng Lei, Jingjing Zhang, Wenkai Nian, Tao Dou, Shiheng An, Lin Zhou and Xiulian Sun

Toxins 2019, 11(3), 145; https://doi.org/10.3390/toxins11030145 - 04 Mar 2019

Cited by 9 | Viewed by 2911

Abstract

The Cydia pomonella granulovirus (CpGV) GP37 has synergistic effects on the infectivity of nucleopolyhedroviruses (NPVs), however, the mechanism employed is unclear. In this study, in vitro and in vivo binding assays indicated that GP37 efficiently bound to the midgut peritrophic membrane (PM) of [...] Read more.

The Cydia pomonella granulovirus (CpGV) GP37 has synergistic effects on the infectivity of nucleopolyhedroviruses (NPVs), however, the mechanism employed is unclear. In this study, in vitro and in vivo binding assays indicated that GP37 efficiently bound to the midgut peritrophic membrane (PM) of Spodoptera exigua larvae. Treatment with GP37 led to the damage of the PM’s compacted structure and the generation of the PM perforations, and the enhancement of the PM’s permeability. qPCR results further demonstrated that GP37 increased the ability of occlusion-derived virions (ODV) to cross the PM. R18-labeling experiments exhibited that GP37 also promoted the fusion of ODVs and insect midgut epithelia. Altogether, our present results revealed that the synergistic mechanism of GP37 to the infectivity of NPV might involve two parts. GP37 damaged the integrity of the PM after binding, which enhanced the PM’s permeability and increased the ability of ODVs to cross the PM, finally facilitating the ODVs reaching the midgut. In addition, GP37 promoted the fusion of ODVs and insect midgut epithelia. Our data expand the understanding of the mechanism used by baculovirus synergistic factors and provide a foundation for the development of high-efficiency baculoviral insecticides. Full article

(This article belongs to the Special Issue Insecticidal Toxins: Advances in Discovery and PestControl Applications)

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Review

Jump to: Research

18 pages, 647 KiB

Open AccessEditor’s ChoiceReview

Repertoire of the Bacillus thuringiensis Virulence Factors Unrelated to Major Classes of Protein Toxins and Its Role in Specificity of Host-Pathogen Interactions

by Yury V. Malovichko, Anton A. Nizhnikov and Kirill S. Antonets

Toxins 2019, 11(6), 347; https://doi.org/10.3390/toxins11060347 - 17 Jun 2019

Cited by 38 | Viewed by 5816

Abstract

Bacillus thuringiensis (Bt) is a Gram-positive soil bacteria that infects invertebrates, predominantly of Arthropoda phylum. Due to its immense host range Bt has become a leading producer of biopesticides applied both in biotechnology and agriculture. Cytotoxic effect of Bt, as [...] Read more.

Bacillus thuringiensis (Bt) is a Gram-positive soil bacteria that infects invertebrates, predominantly of Arthropoda phylum. Due to its immense host range Bt has become a leading producer of biopesticides applied both in biotechnology and agriculture. Cytotoxic effect of Bt, as well as its host specificity, are commonly attributed either to proteinaceous crystal parasporal toxins (Cry and Cyt) produced by bacteria in a stationary phase or to soluble toxins of Vip and Sip families secreted by vegetative cells. At the same time, numerous non-toxin virulence factors of Bt have been discovered, including metalloproteases, chitinases, aminopolyol antibiotics and nucleotide-mimicking moieties. These agents act at each stage of the B. thuringiensis invasion and contribute to cytotoxic properties of Bt strains enhancing toxin activity, ensuring host immune response evasion and participating in extracellular matrix degeneration. In this review we attempt to classify Bt virulence factors unrelated to major groups of protein toxins and discuss their putative role in the establishment of Bt specificity to various groups of insects. Full article

(This article belongs to the Special Issue Insecticidal Toxins: Advances in Discovery and PestControl Applications)

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