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1.
Arch Insect Biochem Physiol ; 104(1): e21661, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-32011765

RESUMO

Polycalin has been confirmed as a binding protein of the Cry toxins in a few Lepidoptera insects, but its function in the action mechanism of Cry1Ac and whether it is involved in resistance evolution are still unclear. In this study, Ligand blot and enzyme-linked immunosorbent assays showed that Helicoverpa armigera polycalin could specifically interact with Cry1Ac with a high affinity (Kd = 118.80 nM). Importantly, antisera blocking polycalin in H. armigera larvae decreased the toxicity of Cry1Ac by 31.84%. Furthermore, the relative gene and protein expressions were lower in Cry1Ac-resistant strain (LF60) than that in Cry1Ac-susceptible strain (LF). These findings indicated that H. armigera polycalin was a possible receptor of Cry1Ac and may be contributed to the resistance to Cry1Ac.

2.
Sci Rep ; 10(1): 301, 2020 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-31942011

RESUMO

MicroRNA-27a/b are small non-coding RNAs which are reported to regulate inflammatory response and cell proliferation. Although some studies have demonstrated that miR-27b is down-regulated in the oral specimens of patients suffering with oral lichen planus (OLP), the molecular mechanism of miR-27b decrease remains a large mystery, and the expression of miR-27a in OLP is not well explored. Here, we demonstrated both miR-27a and miR-27b, compared with healthy controls, were reduced in the oral biopsies, serum and saliva samples derived from OLP patients. The reductions of miR-27a/b were also confirmed in the lipopolysaccharide (LPS)- or activated CD4+ T cell-treated human oral keratinocytes (HOKs). Furthermore, we found vitamin D receptor (VDR) binding sites in the promoters of miR-27a/b genes and verified this finding. We also tested miR-27a/b levels in the oral epithelium from paricalcitol-treated, vitamin D deficient or VDR knockout mice. In the rescue experiments, we confirmed vitamin D and VDR inhibited LPS- or activated CD4+ T cell-induced miR-27a/b reductions in HOKs. In sum, our results show that vitamin D/VDR signaling induces miR-27a/b in oral lichen planus.

3.
Front Physiol ; 10: 1312, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31681018

RESUMO

Helicoverpa armigera is a universal pest around the world that has been extensively used as a model organism for agricultural pests. Calcineurin (CAN) is an important Ca2+-dependent phosphatase that is participated in various biological pathways. Here, we revealed that CAN inhibition significantly arrested H. armigera larval development by reducing larvae weight, prolonging development time and reducing pupate rates. Furthermore, CAN serves as an immune activator and regulates antimicrobial peptide (AMP; cecropin D, attacin, and gloverin) expression by binding with relish transcript factor in H. armigera. This study provides a potential target to control H. armigera by using synergistic agents for pesticides or plant-mediated RNA interference technology.

4.
Arch Insect Biochem Physiol ; 102(3): e21547, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30864250

RESUMO

Bt crop pyramids produce two or more Bt proteins active to broaden the spectrum of action and to delay the development of resistance in exposed insect populations. The cross-resistance between Bt toxins is a vital restriction factor for Bt crop pyramids, which may reduce the effect of pyramid strategy. In this review, the status of the cross-resistance among more than 20 Bt toxins that are most commonly used against 13 insect pests was analyzed. The potential mechanisms of cross-resistance are discussed. The corresponding measures, including pyramid RNA interference and Bt toxin, "high dose/refuge," and so on are advised to be taken for adopting the pyramided strategy to delay the Bt evolution of resistance and control the target pest insect.


Assuntos
Insetos , Controle Biológico de Vetores/métodos , Plantas Geneticamente Modificadas , Animais , Bacillus thuringiensis/genética , Proteínas de Bactérias , Toxinas Bacterianas/genética , Produtos Agrícolas/genética , Endotoxinas , Resistência a Inseticidas , Interferência de RNA
5.
Pest Manag Sci ; 75(4): 1099-1106, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30264537

RESUMO

BACKGROUND: Field-evolved resistance of Helicoverpa zea to Bacillus thuringiensis (Bt) toxin Cry1Ac was first reported more than a decade ago, yet the underlying mechanisms remain elusive. Towards understanding the mechanisms of resistance to Cry1Ac, we analyzed a susceptible (LAB-S) and two resistant (GA and GA-R) strains of H. zea. The GA strain was derived from Georgia and exposed to Bt toxins only in the field. The GA-R strain was derived from the GA strain and selected for increased resistance to Cry1Ac in the laboratory. RESULTS: Resistance to MVPII, a liquid formulation containing a hybrid protoxin similar to Cry1Ac, was 110-fold for GA-R and 7.8-fold for GA relative to LAB-S. In midgut brush border membrane vesicles, activity of alkaline phosphatase and aminopeptidase N did not vary significantly among strains. The activity of total proteases, trypsin-like proteases and chymotrypsin-like proteases was significantly lower for GA-R and GA than LAB-S, but did not differ between GA-R and GA. When H. zea midgut cells were exposed to Cry1Ac protoxin that had been digested with midgut extracts, toxicity was significantly lower for extracts from GA-R and GA relative to extracts from LAB-S, but did not differ between GA-R and GA. Transcriptional analysis showed that none of the five protease genes examined was associated with the decline in Cry1Ac activation in GA-R and GA relative to LAB-S. CONCLUSION: The results suggest that decreased Cry1Ac activation is a contributing field-selected mechanism of resistance that helps explain the reduced susceptibility of the GA-R and GA strains. Relative to the LAB-S strain, the two Cry1Ac-resistant strains had lower total protease, trypsin and chymotrypsin activities, a lower Cry1Ac activation rate, and Cry1Ac protoxin incubated with their midgut extracts was less toxic to H. zea midgut cells. © 2018 Society of Chemical Industry.


Assuntos
Proteínas de Bactérias/farmacologia , Endotoxinas/farmacologia , Proteínas Hemolisinas/farmacologia , Proteínas de Insetos/genética , Resistência a Inseticidas/genética , Inseticidas/farmacologia , Mariposas/genética , Peptídeo Hidrolases/genética , Animais , Bacillus thuringiensis/química , Trato Gastrointestinal/metabolismo , Proteínas de Insetos/metabolismo , Larva/enzimologia , Larva/genética , Larva/crescimento & desenvolvimento , Mariposas/enzimologia , Mariposas/crescimento & desenvolvimento , Peptídeo Hidrolases/metabolismo
6.
Front Physiol ; 9: 1653, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30524311

RESUMO

Helicoverpa armigera can develop resistance to Bacillus thuringiensis (Bt), which threaten the long-term success of Bt crops. In the present study, RNAseq was employed to investigate the midgut genes response to strains with different levels of resistance (LF5, LF10, LF20, LF30, LF60, and LF120) in H. armigera. Results revealed that a series of differentially expressed unigenes (DEGs) were expressed significantly in resistant strains compared with the LF-susceptible strain. Nine trypsin genes, ALP2, were downregulated significantly in all the six resistant strains and further verified by qRT-PCR, indicating that these genes may be used as markers to monitor and manage pest resistance in transgenic crops. Most importantly, the differences in DEG functions in the different resistant strains revealed that different resistance mechanisms may develop during the evolution of resistance. The immune and detoxification processes appear to be associated with the low-level resistance (LF5 strain). Metabolic process-related macromolecules possibly lead to resistance to Cry1Ac in the LF10 and LF20 strains. The DEGs involved in the "proton-transporting V-type ATPase complex" and the "proton-transporting two-sector ATPase complex" were significantly expressed in the LF30 strain, probably causing resistance to Cry1Ac in the LF30 strain. The DEGs involved in binding and iron ion homeostasis appear to lead to high-level resistance in the LF60 and LF120 strains, respectively. The multiple genes and different pathways seem to be involved in Cry1Ac resistance depending on the levels of resistance. Although the mechanisms of resistance are very complex in H. armigera, a main pathway seemingly exists, which contributes to resistance in each level of resistant strain. Altogether, the findings in the current study provide a transcriptome-based foundation for identifying the functional genes involved in Cry1Ac resistance in H. armigera.

7.
PLoS One ; 13(9): e0204154, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30216388

RESUMO

Helicoverpa armigera is an universal pest around the world, which has recovered again in recent years because of the adjustment of cropping structure and resistance to Bacillus thuringiensis (Bt) in China. As a new insecticide spinetoram is extensively used to control many pest insects, including H. armigera. However the lethal and sublethal effects of spinetoram on cotton bollworm have not been assessed. In the present study, the toxicity of spinetoram against cotton bollworm was tested under laboratory conditions. Results demonstrated spinetoram showed an excellent activity against H. armigera, especially, against Bt (Cry1Ac) resistant H. armigera. Treatment with spinetoram at the doses of 0.19 mg/kg and 0.36 mg/kg (LC8 and LC20 after 24h oral exposure) significantly arrested the development of surviving larvae and caused significant decrease in larvae wet weight. Besides, the survivors after spinetoram treatments showed significant reduction of pupation ratio, pupal weight, emergence ratio, longevity and fecundity of adults. At same time, spinetoram treatments resulted in significant increase in the prepupal and pupal periods of survivors. In summary, these results showed that spinetoram could be used as an effective pesticide to control H. armigera, especially Cry1Ac-ressitacne, consequently to take both lethal and sublethal effects to cotton bollworm into consideration in cotton bollworm control strategy.


Assuntos
Gossypium/parasitologia , Macrolídeos/toxicidade , Mariposas/efeitos dos fármacos , Testes de Toxicidade Aguda , Animais , Proteínas de Bactérias/toxicidade , Peso Corporal/efeitos dos fármacos , Endotoxinas/toxicidade , Fertilidade/efeitos dos fármacos , Proteínas Hemolisinas/toxicidade , Resistência a Inseticidas/efeitos dos fármacos , Larva/efeitos dos fármacos , Mariposas/fisiologia , Pupa/efeitos dos fármacos
8.
Front Physiol ; 9: 745, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-29971014

RESUMO

A pyramid strategy combining the crystal (Cry) 1A and 2A toxins in Bacillus thuringiensis (Bt) crops are active against many species of insects and nematode larvae. It has been widely used to delay pest adaption to genetically modified plants and broaden the insecticidal spectrum in many countries. Unfortunately, Cry2A can also bind with the specific receptor proteins of Cry1A. ATP-binding cassette (ABC) transporters can interact with Cry1A toxins as receptors in the insect midgut, and ABC transporter mutations result in resistance to Bt proteins. However, there is limited knowledge of the ABC transporters that specifically bind to Cry2Ab. Here, we cloned the ABCC1 gene in Helicoverpa armigera, which expressed at all larval stages and in nine different tissues. Expression levels were particularly high in fifth-instar larvae and Malpighian tubules. The two heterologously expressed HaABCC1 transmembrane domain peptides could specifically bind to Cry2Ab with high affinity levels. Moreover, transfecting HaABCC1 into the Spodoptera frugiperda nine insect cell significantly increased its mortality when exposed to Cry2Ab in vitro, and silencing HaABCC1 in H. armigera by RNA interference significantly reduced the mortality of larvae exposed to Cry2Ab in vivo. Altogether current results suggest that HaABCC1 serves as a functional receptor for Cry2Ab.

9.
Insect Sci ; 25(4): 655-666, 2018 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-28247982

RESUMO

While Cry1Ac has been known to bind with larval midgut proteins cadherin, APN (amino peptidase N), ALP (alkaline phosphatase) and ABCC2 (adenosine triphosphate-binding cassette transporter subfamily C2), little is known about the receptors of Cry2Ab. To provide a clue to the receptors of Cry2Ab, we tested the baseline cytotoxicity of activated Cry1Ac and Cry2Ab against the midgut and fat body cell lines of Helicoverpa zea and the ovary cell line of Spodoptera frugiperda (SF9). As expected, the descending order of cytotoxicity of Cry1Ac against the three cell lines in terms of 50% lethal concetration (LC50 ) was midgut (31.0 µg/mL) > fat body (59.0 µg/mL) and SF9 cell (99.6 µg/mL). By contrast, the fat body cell line (LC50 = 7.55 µg/mL) was about twice more susceptible to Cry2Ab than the midgut cell line (16.0 µg/mL), the susceptibility of which was not significantly greater than that of SF9 cells (27.0 µg/mL). Further, ligand blot showed the binding differences between Cry1Ac and Cry2Ab in the three cell lines. These results indicated that the receptors of Cry2Ab were enriched in fat body cells and thus largely different from the receptors of Cry1Ac, which were enriched in midgut cells.


Assuntos
Endotoxinas/toxicidade , Proteínas Hemolisinas/toxicidade , Animais , Bacillus thuringiensis/química , Proteínas de Bactérias/metabolismo , Linhagem Celular , Endotoxinas/metabolismo , Corpo Adiposo , Trato Gastrointestinal , Proteínas Hemolisinas/metabolismo , Ligação Proteica , Células Sf9 , Spodoptera
10.
J Invertebr Pathol ; 151: 197-200, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-29111356

RESUMO

In this study, the results showed that the population of midgut bacteria and larval mortality due to Cry1Ac are significantly reduced in antibiotic-treated larvae from Bt-susceptible, -resistant and field-collected strains (96S, BtR, FS respectively) of Helicoverpa armigera. The percentage reduction of larval mortality with increasing concentrations of antibiotics was significantly different among strains with the smallest effect observed in FS. It has been suggested that antibiotics could influence the toxicity of Cry1Ac, possibly by eliminating gut bacteria, hence gut bacteria might be playing essential roles in Bt-induced killing of H. armigera. But elimination of midgut microflora with antibiotics had no effect on resistance level.


Assuntos
Antibacterianos/farmacologia , Proteínas de Bactérias/metabolismo , Endotoxinas/metabolismo , Microbioma Gastrointestinal/efeitos dos fármacos , Proteínas Hemolisinas/metabolismo , Resistência a Inseticidas/efeitos dos fármacos , Mariposas/microbiologia , Controle Biológico de Vetores/métodos , Animais , Mariposas/efeitos dos fármacos
11.
Sci Rep ; 7: 46555, 2017 05 10.
Artigo em Inglês | MEDLINE | ID: mdl-28488696

RESUMO

A pyramid strategy combining the Cry1A and Cry2A toxins in Bt crops has been widely used throughout the world to delay pest adaption to transgenic crops and broaden the insecticidal spectrum. Midgut membrane-bound cadherin (CAD), aminopeptidase-N (APN) and alkaline phosphatase (ALP) are important for Cry1A toxicity in some lepidopteran larvae, but the proteins that bind Cry2A in the midgut of target insects and their role in the Cry2A mechanism of action are still unclear. In this study, we found that heterologously expressed CAD, APN4 and ALP2 peptides from the midgut of Helicoverpa armigera could bind to the Cry2Aa toxin with a high affinity. Additionally, the efficiency of Cry2Aa insecticidal activity against H. armigera larvae was obviously reduced after the genes encoding these proteins were silenced with specific siRNAs: CAD- and ALP2-silenced larvae showed significantly similar reductions in mortality due to the Cry2Aa toxin (41.67% and 43.06%, respectively), whereas a larger reduction in mortality was observed in APN4-silenced larvae (61.11%) than in controls. These results suggest that CAD, APN4 and ALP2 are involved in the mechanism of action of Cry2Aa in H. armigera and may play important functional roles in the toxicity of the Cry2Aa toxin.


Assuntos
Fosfatase Alcalina/metabolismo , Bacillus thuringiensis , Proteínas de Bactérias/farmacologia , Antígenos CD13/metabolismo , Caderinas/metabolismo , Endotoxinas/farmacologia , Proteínas Hemolisinas/farmacologia , Proteínas de Insetos/metabolismo , Inseticidas/farmacologia , Intestinos , Mariposas/metabolismo , Animais , Larva/metabolismo
12.
J Insect Physiol ; 98: 101-107, 2017 04.
Artigo em Inglês | MEDLINE | ID: mdl-28034678

RESUMO

Cry1A and Cry2A toxins, which are widely used in Bt transgenic crops, can specifically bind to insect midguts and exert their insecticidal effects. There are interactions between insect midgut-binding proteins and Cry1A toxins; however, little is known about the insect protein that specifically binds to Cry2A. Midgut membrane-bound alkaline phosphatases (ALPs), which are important for the binding of proteins to Cry1A, play dominant roles in Cry1A-mediated toxicity in some lepidopteran larvae. In this study, we cloned and expressed one partial ALP2 peptide from susceptible Spodoptera exigua larvae and studied the binding characteristics of SeALP2 with Cry2Aa. The ALPs proteins was expressed at all larval stages and highly expressed in the first and second instar larvae. The heterologously expressed SeALP2 peptide bound specifically to Cry2Aa with a high affinity. Knocking down ALP2 in vivo revealed that it plays an important role in the susceptibility of S. exigua to Cry2Aa. Based on these findings, we propose that ALP2 in S. exigua serves as a functional receptor for Cry2Aa.


Assuntos
Fosfatase Alcalina/genética , Proteínas de Bactérias/farmacologia , Endotoxinas/farmacologia , Proteínas Hemolisinas/farmacologia , Proteínas de Insetos/genética , Spodoptera/genética , Fosfatase Alcalina/metabolismo , Animais , Clonagem Molecular , DNA Complementar/genética , DNA Complementar/metabolismo , Proteínas de Insetos/metabolismo , Larva/genética , Larva/crescimento & desenvolvimento , Larva/metabolismo , Larva/microbiologia , Análise de Sequência de DNA , Spodoptera/crescimento & desenvolvimento , Spodoptera/metabolismo , Spodoptera/microbiologia
13.
PLoS One ; 11(6): e0156560, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27257885

RESUMO

Crystalline (Cry) proteins from Bacillus thuringiensis (Bt) are used extensively for insect control in sprays and transgenic plants, but their efficacy is reduced by evolution of resistance in pests. Here we evaluated reduced activation of Cry1Ac protoxin as a potential mechanism of resistance in the invasive pest Helicoverpa armigera. Based on the concentration killing 50% of larvae (LC50) for a laboratory-selected resistant strain (LF120) divided by the LC50 for its susceptible parent strain (LF), the resistance ratio was 1600 for Cry1Ac protoxin and 1200 for trypsin-activated Cry1Ac toxin. The high level of resistance to activated toxin as well as to protoxin indicates reduced activation of protoxin is not a major mechanism of resistance to Cry1Ac in LF120. For both insect strains, treatment with either the trypsin inhibitor N-a-tosyl-L-lysine chloromethyl ketone (TLCK) or the chymotrypsin inhibitor N-a-tosyl-L-phenylalanine chloromethyl ketone (TPCK) did not significantly affect the LC50 of Cry1Ac protoxin. Enzyme activity was higher for LF than LF120 for trypsin-like proteases, but did not differ between strains for chymotrypsin-like proteases. The results here are consistent with previous reports indicating that reduced activation of protoxin is generally not a major mechanism of resistance to Bt proteins.


Assuntos
Toxinas Bacterianas/farmacologia , Mariposas/efeitos dos fármacos , Precursores de Proteínas/farmacologia , Animais , Controle de Insetos , Resistência a Inseticidas , Larva/efeitos dos fármacos , Tosilina Clorometil Cetona/farmacologia
14.
Sci Rep ; 6: 19179, 2016 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-26755166

RESUMO

Lepidopteran midgut aminopeptidases N (APNs) are phylogenetically divided into eight clusters, designated as APN1-8. Although APN1 has been implicated as one of the receptors for Cry1Ac in several species, its potential role in the mode of action of Cry2Ab has not been functionally determined so far. To test whether APN1 also acts as one of the receptors for Cry1Ac in Helicoverpa zea and even for Cry2Ab in this species, we conducted a gain of function analysis by heterologously expressing H. zea APN1 (HzAPN1) in the midgut and fat body cell lines of H. zea and the ovarian cell line of Spodoptera frugiperda (Sf9) and a loss of function analysis by RNAi (RNA interference) silencing of the endogenous APN1 in the three cell lines using the HzAPN1 double strand RNA (dsRNA). Heterologous expression of HzAPN1 significantly increased the susceptibility of the three cell lines to Cry1Ac, but had no effects on their susceptibility to Cry2Ab. Knocking down of the endogenous APN1 made the three cell lines resistant to Cry1Ac, but didn't change cell lines susceptibility to Cry2Ab. The findings from this study demonstrate that HzAPN1 is a functional receptor of Cry1Ac, but not Cry2Ab.


Assuntos
Aminopeptidases/metabolismo , Endotoxinas/metabolismo , Mariposas/metabolismo , Aminopeptidases/genética , Animais , Linhagem Celular , Endotoxinas/toxicidade , Trato Gastrointestinal/metabolismo , Expressão Gênica , Técnicas de Silenciamento de Genes , Mariposas/genética , Ligação Proteica , Transfecção , Vesículas Transportadoras/metabolismo
15.
Insect Sci ; 23(4): 649-54, 2016 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-26314801

RESUMO

Transgenic crops are increasingly promoted for their practical effects on suppressing certain insect pests, but all transgenic crops are not equally successful. The insect pests can easily develop resistance against single Bacillus thuringiensis (Bt) toxin transgenic crops. Therefore, transgenic crops including two or more mixed Bt-toxins can solve this problem by delaying the resistance development and killing the majority of targeted pests before the evolution of resistance. It is important to test the controlling effects of transgenic crops including multiple mixed toxins on a particular insect pest. Previous research has checked the cross-resistance and interactions between Bt toxins Cry1Ac and Cry2Ab against one susceptible and four resistant strains of cotton bollworm. The results showed that independence was the main interaction type between two toxins for the susceptible strain, whereas synergism was the main interaction type for any one resistant strain. However, the optimal combinations of two toxins were not obtained. In the present study, we developed two multi-exponential equations (namely bi- and tri-exponential equations) to describe the combination effects of two Bt toxins. Importantly, the equations can provide predictions of combination effects of different continuous concentrations of two toxins. We compared these two multi-exponential equations with the generalized linear model (GLM) in describing the combination effects, and found that the bi- and tri-exponential equations are better than GLM. Moreover, the bi-exponential equation can also provide the optimal dose combinations for two toxins.


Assuntos
Bacillus thuringiensis/metabolismo , Endotoxinas/metabolismo , Proteínas Hemolisinas/metabolismo , Mariposas/efeitos dos fármacos , Animais , Endotoxinas/toxicidade , Gossypium/parasitologia , Proteínas Hemolisinas/toxicidade , Resistência a Inseticidas , Larva/efeitos dos fármacos , Modelos Teóricos , Mariposas/fisiologia
16.
Sci Rep ; 5: 15107, 2015 Oct 12.
Artigo em Inglês | MEDLINE | ID: mdl-26455902

RESUMO

Transgenic crops that produce Bacillus thuringiensis (Bt) proteins for pest control are grown extensively, but insect adaptation can reduce their effectiveness. Established mode of action models assert that Bt proteins Cry1Ab and Cry1Ac are produced as inactive protoxins that require conversion to a smaller activated form to exert toxicity. However, contrary to this widely accepted paradigm, we report evidence from seven resistant strains of three major crop pests showing that Cry1Ab and Cry1Ac protoxins were generally more potent than the corresponding activated toxins. Moreover, resistance was higher to activated toxins than protoxins in eight of nine cases evaluated in this study. These data and previously reported results support a new model in which protoxins and activated toxins kill insects via different pathways. Recognizing that protoxins can be more potent than activated toxins against resistant insects may help to enhance and sustain the efficacy of transgenic Bt crops.


Assuntos
Bacillus thuringiensis/química , Proteínas de Bactérias/toxicidade , Endotoxinas/toxicidade , Proteínas Hemolisinas/toxicidade , Proteínas de Insetos/antagonistas & inibidores , Precursores de Proteínas/toxicidade , Animais , Bacillus thuringiensis/patogenicidade , Bacillus thuringiensis/fisiologia , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Produtos Agrícolas/genética , Produtos Agrícolas/parasitologia , Endotoxinas/química , Endotoxinas/genética , Expressão Gênica , Proteínas Hemolisinas/química , Proteínas Hemolisinas/genética , Proteínas de Insetos/química , Proteínas de Insetos/metabolismo , Mucosa Intestinal/metabolismo , Intestinos/efeitos dos fármacos , Intestinos/fisiologia , Larva/efeitos dos fármacos , Larva/metabolismo , Larva/fisiologia , Lepidópteros/efeitos dos fármacos , Lepidópteros/metabolismo , Lepidópteros/fisiologia , Modelos Moleculares , Plantas Geneticamente Modificadas , Ligação Proteica , Precursores de Proteínas/química , Precursores de Proteínas/genética , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Transgenes
17.
J Invertebr Pathol ; 132: 149-156, 2015 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-26458274

RESUMO

To delay evolution of resistance by insect pests, farmers are rapidly increasing their use of transgenic crops producing two or more Bacillus thuringiensis (Bt) toxins that kill the same pest. A key condition favoring durability of these "pyramided" crops is the absence of cross-resistance between toxins. Here we evaluated cross-resistance in the major lepidopteran pest Helicoverpa zea (Boddie) to Bt toxins used in pyramids. In the laboratory, we selected a strain of this pest with Bt toxin Cry1Ac followed by selection with MVP II, a formulation containing a hybrid protoxin that is identical to Cry1Ac in the active portion of the toxin and 98.5% identical overall. We calculated the resistance ratio as the EC50 (concentration causing mortality or failure to develop beyond the first instar of 50% of larvae) for the laboratory-selected strain divided by the EC50 for its field-derived parent strain that was not selected in the laboratory. The resistance ratio was 20.0-33.9 (mean=27.0) for MVP II, 57.0 for Cry1Ac, 51.3 for Cry1A.105, 22.4 for Cry1Ab, 3.3 for Cry2Ab, 1.8 for Cry1Fa, and 1.6 for Vip3Aa. Resistance ratios were 2.9 for DiPel ES and 2.0 for Agree VG, which are commercial Bt spray formulations containing Cry1Ac, other Bt toxins, and Bt spores. By the conservative criterion of non-overlap of 95% fiducial limits, the EC50 was significantly higher for the selected strain than its parent strain for MVP II, Cry1Ac, Cry1A.105, Cry1Ab, Cry2Ab and DiPel ES. For Cry1Fa, Vip3Aa, and Agree VG, significantly lower susceptibility to a high concentration indicated low cross-resistance. The resistance ratio for toxins other than Cry1Ac was associated with their amino acid sequence similarity to Cry1Ac in domain II. Resistance to Cry1Ac and the observed cross-resistance to other Bt toxins could accelerate evolution of H. zea resistance to currently registered Bt sprays and pyramided Bt crops.


Assuntos
Proteínas de Bactérias/química , Produtos Agrícolas/genética , Endotoxinas/química , Proteínas Hemolisinas/química , Resistência a Inseticidas , Mariposas/efeitos dos fármacos , Animais , Larva/efeitos dos fármacos , Plantas Geneticamente Modificadas , Análise de Sequência de Proteína
18.
Sci Rep ; 5: 7714, 2015 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-25586723

RESUMO

To delay evolution of pest resistance to transgenic crops producing insecticidal proteins from Bacillus thuringiensis (Bt), the "pyramid" strategy uses plants that produce two or more toxins that kill the same pest. We conducted laboratory diet experiments with the cotton bollworm, Helicoverpa armigera, to evaluate cross-resistance and interactions between two toxins in pyramided Bt cotton (Cry1Ac and Cry2Ab). Selection with Cry1Ac for 125 generations produced 1000-fold resistance to Cry1Ac and 6.8-fold cross-resistance to Cry2Ab. Selection with Cry2Ab for 29 generations caused 5.6-fold resistance to Cry2Ab and 61-fold cross-resistance to Cry1Ac. Without exposure to Bt toxins, resistance to both toxins decreased. For each of the four resistant strains examined, 67 to 100% of the combinations of Cry1Ac and Cry2Ab tested yielded higher than expected mortality, reflecting synergism between these two toxins. Results showing minor cross-resistance to Cry2Ab caused by selection with Cry1Ac and synergism between these two toxins against resistant insects suggest that plants producing both toxins could prolong the efficacy of Bt cotton against this pest in China. Including toxins against which no cross-resistance occurs and integrating Bt cotton with other control tactics could also increase the sustainability of management strategies.


Assuntos
Proteínas de Bactérias/toxicidade , Endotoxinas/toxicidade , Gossypium/parasitologia , Proteínas Hemolisinas/toxicidade , Resistência a Inseticidas/efeitos dos fármacos , Mariposas/efeitos dos fármacos , Animais , Mariposas/fisiologia
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