Downregulation of APN1 and mutation in Bt Cry1Ac-resistant are genetically independent.

The resistance to the insecticidal protein Cry1Ac from the bacterium (Bt) in the cabbage looper, , has previously been identified to be associated with a frameshift mutation in the ABC transporter ABCC2 gene and with altered expression of the aminopeptidase N (APN) genes and , shown as missing of the 110-kDa APN1 (phenotype APN1¯) in larval midgut brush border membrane vesicles (BBMV). In this study, genetic linkage analysis identified that the APN1¯ phenotype and the mutation in Cry1Ac-resistant segregated independently, although they were always associated under Cry1Ac selection. The mutation and APN1¯ phenotype were separated into two strains respectively.

Receptor interactions of protoxin and activated Vip3Aa structural conformations in Spodoptera exigua.

Background: The Vip3Aa insecticidal protein, produced by Bacillus thuringiensis, has been effectively used in commercial Bt-crops to manage lepidopteran pests. Upon ingestion by larvae, the protoxin is processed by midgut proteases into the activated protein and binds specifically to its receptors in the midgut, leading to insect mortality. Cryo-EM resolution of the trypsin-processed Vip3Aa protein unveiled structural remodelling of the N-terminal region during the transition from protoxin to activated protein.

New Paralogs of the Transporter as Potential Receptors for Bt Cry1A Proteins.

The ATP-binding cassette (ABC) transporters are a superfamily of membrane proteins. These active transporters are involved in the export of different substances such as xenobiotics. ABC transporters from subfamily C (ABCC) have also been described as functional receptors for different insecticidal proteins from (Bt) in several lepidopteran species.

Mpp23Aa/Xpp37Aa Insecticidal Proteins from (Bacillales: Bacillaceae) Are Highly Toxic to (Coleoptera: Curculionidae) Larvae.

The beetle Boheman, 1843, is the main cotton pest, causing enormous losses in cotton. The breeding of genetically modified plants with resistance is seen as an important control strategy. However, the identification of molecules with high toxicity to this insect remains a challenge.

In vivo competition assays between Vip3 proteins confirm the occurrence of shared binding sites in Spodoptera littoralis.

Due to their different specificity, the use of Vip3 proteins from Bacillus thuringiensis in combination with the conventionally used Cry proteins in crop protection is being essential to counteract the appearance of insect resistance. Therefore, understanding the mode of action of Vip3 proteins is crucial for their better application, with special interest on the binding to membrane receptors as the main step for specificity. Derived from in vitro heterologous competition binding assays using I-Vip3A and other Vip3 proteins as competitors, it has been shown that Vip3 proteins share receptors in Spodoptera frugiperda and Spodoptera exigua brush border membrane vesicles (BBMV).

Alteration of a Cry1A Shared Binding Site in a Cry1Ab-Selected Colony of .

The Asian corn borer, (Guenée, 1854), is a highly damaging pest in Asia and the Pacific islands, and larvae feed mainly from corn crops. To determine the suitability of Bt-corn technology for the future control of this pest, understanding the potential to develop resistance to Cry1Ab and the basis of cross-resistance to other Cry1 proteins is of great interest. Here, we have explored the binding of Cry1A proteins to brush border membrane vesicles from two colonies, one susceptible (ACB-BtS) and one laboratory-selected with Cry1Ab (ACB-AbR).

Comparison of in vitro and in vivo binding site competition of Bacillus thuringiensis Cry1 proteins in two important maize pests.

Background: Binding site models, derived from in vitro competition binding studies, have been widely used for predicting potential cross-resistance among insecticidal proteins from Bacillus thuringiensis. However, because discrepancies have been found between binding data and observed cross-resistance patterns in some insect species, new tools are required to study the functional relevance of the shared binding sites.

Results: Here, an in vivo approach has been applied to the competition studies to establish the functional relevance of shared binding sites as determined by in vitro competition assays.

Critical Domains in the Specific Binding of Radiolabeled Vip3Af Insecticidal Protein to Brush Border Membrane Vesicles from spp. and Cultured Insect Cells.

Vegetative insecticidal proteins (Vip3) from Bacillus thuringiensis have been used, in combination with Cry proteins, to better control insect pests and as a strategy to delay the evolution of resistance to Cry proteins in Bt crops (crops protected from insect attack by the expression of proteins from B. thuringiensis). In this study, we have set up the conditions to analyze the specific binding of I-Vip3Af to Spodoptera frugiperda and Spodoptera exigua brush border membrane vesicles (BBMV).

Hetero-oligomerization of Bacillus thuringiensis Cry1A proteins enhance binding to the ABCC2 transporter of Spodoptera exigua.

The ATP binding cassette (ABC) transporters are membrane proteins that can act as putative receptors for Cry proteins from Bacillus thuringiensis (Bt) in the midgut of different insects. For the beet armyworm, Spodoptera exigua, ABCC2 and ABCC3 have been found to interact with Cry1A proteins, the main insecticidal proteins used in Bt crops, as well as Bt-based pesticides. The ABCC2 has shown to have specific binding towards Cry1Ac and is involved in the toxic process of Cry1A proteins, but the role of this transporter and how it relates with the Cry1A proteins is still unknown.

The Rapid Evolution of Resistance to Vip3Aa Insecticidal Protein in (Walker) Is Not Related to Altered Binding to Midgut Receptors.

Laboratory selection for resistance of field populations is a well-known and useful tool to understand the potential of insect populations to evolve resistance to insecticides. It provides us with estimates of the frequency of resistance alleles and allows us to study the mechanisms by which insects developed resistance to shed light on the mode of action and optimize resistance management strategies. Here, a field population of was subjected to laboratory selection with either Vip3Aa, Cry1Ab, or Cry1F insecticidal proteins from .

Response Mechanisms of Invertebrates to and Its Pesticidal Proteins.

Extensive use of chemical insecticides adversely affects both environment and human health. One of the most popular biological pest control alternatives is bioinsecticides based on This entomopathogenic bacterium produces different protein types which are toxic to several insect, mite, and nematode species. Currently, insecticidal proteins belonging to the Cry and Vip3 groups are widely used to control insect pests both in formulated sprays and in transgenic crops.

Toxins: Functional Characterization and Mechanism of Action.

()-based products are the most successful microbial insecticides to date [...

The Independent Biological Activity of Cry23Aa Protein Against .

The Cry23Aa/Cry37Aa proteins from (Bt) have been described toxic to larvae. In general, it is believed that Cry23Aa and Cry37Aa act jointly to exert the insecticidal activity, while there is no evidence of their toxicity individually. Therefore, in the present study, the contribution of each protein in the insecticidal activity toward larvae has been assessed.

Effect of substitutions of key residues on the stability and the insecticidal activity of Vip3Af from Bacillus thuringiensis.

Modern agriculture demands for more sustainable agrochemicals to reduce the environmental and health impact. The whole process of the discovery and development of new active substances or control agents is sorely slow and expensive. Vegetative insecticidal proteins (Vip3) from Bacillus thuringiensis are specific toxins against caterpillars with a potential capacity to broaden the range of target pests.

Reduced Membrane-Bound Alkaline Phosphatase Does Not Affect Binding of Vip3Aa in a Resistant Colony.

The Vip3Aa insecticidal protein from (Bt) is produced by specific transgenic corn and cotton varieties for efficient control of target lepidopteran pests. The main threat to this technology is the evolution of resistance in targeted insect pests and understanding the mechanistic basis of resistance is crucial to deploy the most appropriate strategies for resistance management. In this work, we tested whether alteration of membrane receptors in the insect midgut might explain the >2000-fold Vip3Aa resistance phenotype in a laboratory-selected colony of (Vip-Sel).

The ABCC2 Acts as a Cry1A Receptor Independently of its Nucleotide Binding Domain II.

ABC proteins are primary-active transporters that require the binding and hydrolysis of ATP to transport substrates across the membrane. Since the first report of an ABCC2 transporter as receptor of Cry1A toxins, the number of ABC transporters known to be involved in the mode of action of Cry toxins has increased. In , a mutation in the gene is described as genetically linked to resistance to the Bt-product Xentari.

Artefactual band patterns by SDS-PAGE of the Vip3Af protein in the presence of proteases mask the extremely high stability of this protein.

Vip3 proteins are secretable proteins from Bacillus thuringiensis with important characteristics for the microbiological control of agricultural pests. The exact details of their mode of action are yet to be disclosed and the crystallographic structure is still unknown. Vip3 proteins are expressed as protoxins that have to be activated by the insect gut proteases.

Role of Bacillus thuringiensis Cry1A toxins domains in the binding to the ABCC2 receptor from Spodoptera exigua.

Cry proteins from Bacillus thuringiensis (Bt) have been used to control insect pests either as formulated sprays or as in Bt-crops. However, field-evolved resistance to Bt proteins is threatening the long-term use of Bt products. The SeABCC2 locus has been genetically linked to resistance to a Bt bioinsecticide (Xentari™) in Spodoptera exigua (a mutation producing a truncated form of the transporter lacking an ATP binding domain was found in the resistant insects).

Changes in gene expression and apoptotic response in Spodoptera exigua larvae exposed to sublethal concentrations of Vip3 insecticidal proteins.

The insecticidal Vip3 proteins from Bacillus thuringiensis (Bt), along with the classical Bt Cry proteins, are currently used in Bt-crops to control insect pests, since they do not share the same mode of action. Here we characterized the response of Spodoptera exigua larvae after Vip3 challenge. The expression profile of 47 genes was analyzed in larvae challenged with three concentrations of Vip3Ca.

Unshared binding sites for Bacillus thuringiensis Cry3Aa and Cry3Ca proteins in the weevil Cylas puncticollis (Brentidae).

Bacillus thuringiensis Cry3Aa and Cry3Ca proteins have been reported to be toxic against the African sweetpotato pest Cylas puncticollis. In the present work, the binding sites of these proteins in C. puncticollis brush border vesicles suggest the occurrence of different binding sites, but only one of them is shared.

Insecticidal spectrum and mode of action of the Bacillus thuringiensis Vip3Ca insecticidal protein.

The Vip3Ca protein, discovered in a screening of Spanish collections of Bacillus thuringiensis, was known to be toxic to Chrysodeixis chalcites, Mamestra brassicae and Trichoplusia ni. In the present study, its activity has been tested with additional insect species and we found that Cydia pomonella is moderately susceptible to this protein. Vip3Ca (of approximately 90kDa) was processed to an approximately 70kDa protein when incubated with midgut juice in all tested species.

Susceptibility, mechanisms of response and resistance to Bacillus thuringiensis toxins in Spodoptera spp.

Bioinsecticides based on Bacillus thuringiensis have long been used as an alternative to synthetic insecticides to control insect pests. In this review, we focus on insects of the genus Spodoptera, including relevant polyphagous species that are primary and secondary pests of many crops, and how B. thuringiensis toxins can be used for Spodoptera spp.

Binding analysis of Bacillus thuringiensis Cry1 proteins in the sugarcane borer, Diatraea saccharalis (Lepidoptera: Crambidae).

Sugarcane borer (Diatraea saccharalis, F.) is an important corn pest in South America and United States. The aim of the present study was to analyze the susceptibility and binding interactions of three Cry1A proteins and Cry1Fa in a Brazilian D.

Shared binding sites for the Bacillus thuringiensis proteins Cry3Bb, Cry3Ca, and Cry7Aa in the African sweet potato pest Cylas puncticollis (Brentidae).

Bacillus thuringiensis Cry3Bb, Cry3Ca, and Cry7Aa have been reported to be toxic against larvae of the genus Cylas, which are important pests of sweet potato worldwide and particularly in sub-Saharan Africa. However, relatively little is known about the processing and binding interactions of these coleopteran-specific Cry proteins. The aim of the present study was to determine whether Cry3Bb, Cry3Ca, and Cry7Aa proteins have shared binding sites in Cylas puncticollis to orient the pest resistance strategy by genetic transformation.

Different binding sites for Bacillus thuringiensis Cry1Ba and Cry9Ca proteins in the European corn borer, Ostrinia nubilalis (Hübner).

Binding studies using (125)I-Cry9Ca and biotinylated-Cry1Ba proteins showed the occurrence of independent binding sites for these proteins in Ostrinia nubilalis. Our results, along with previously available binding data, indicate that combinations of Cry1A or Cry1Fa proteins with Cry1Ba and/or Cry9Ca could be a good strategy for the resistance management of O. nubilalis.