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Characterization of the resistance to Vip3Aa in Helicoverpa armigera from Australia and the role of midgut processing and receptor binding.

Chakroun M, Banyuls N, Walsh T, Downes S, James B, Ferré J - Sci Rep (2016)

Bottom Line: We found that, although relatively high, the frequency of alleles for resistance to Vip3Aa in field populations of H. armigera in Australia did not increase over the past four seasons until 2014/15.Vip3Aa-resistance does not confer cross-resistance to Cry1Ac or Cry2Ab.Proteolytic conversion of Vip3Aa protoxin into the activated toxin rendered the same products, though it was significantly slower in resistant insects.

View Article: PubMed Central - PubMed

Affiliation: ERI of Biotechnology and Biomedicine (BIOTECMED), Universitat de València, 46100 Burjassot, Spain.

ABSTRACT
Crops expressing genes from Bacillus thuringiensis (Bt crops) are among the most successful technologies developed for the control of pests but the evolution of resistance to them remains a challenge. Insect resistant cotton and maize expressing the Bt Vip3Aa protein were recently commercialized, though not yet in Australia. We found that, although relatively high, the frequency of alleles for resistance to Vip3Aa in field populations of H. armigera in Australia did not increase over the past four seasons until 2014/15. Three new isofemale lines were determined to be allelic with previously isolated lines, suggesting that they belong to one common gene and this mechanism is relatively frequent. Vip3Aa-resistance does not confer cross-resistance to Cry1Ac or Cry2Ab. Vip3Aa was labeled with (125)I and used to show specific binding to H. armigera brush-border membrane vesicles (BBMV). Binding was of high affinity (Kd = 25 and 19 nM for susceptible and resistant insects, respectively) and the concentration of binding sites was high (Rt = 140 pmol/mg for both). Despite the narrow-spectrum resistance, binding of (125)I-labeled Vip3Aa to BBMV of resistant and susceptible insects was not significantly different. Proteolytic conversion of Vip3Aa protoxin into the activated toxin rendered the same products, though it was significantly slower in resistant insects.

No MeSH data available.


Related in: MedlinePlus

Binding of 125I-Vip3Aa to BBMV from GR (susceptible) (●, ○, solid lines) and SP85 (resistant) (◼, ◻, broken lines) colonies at increasing concentrations of BBMV.The figure is representative of two independent experiments with different batches of labeled toxin.
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f2: Binding of 125I-Vip3Aa to BBMV from GR (susceptible) (●, ○, solid lines) and SP85 (resistant) (◼, ◻, broken lines) colonies at increasing concentrations of BBMV.The figure is representative of two independent experiments with different batches of labeled toxin.

Mentions: Specific binding of 125I-Vip3Aa to H. armigera BBMV was shown by incubating the labeled toxin in the absence and the presence of an excess of unlabeled Vip3Aa (Fig. 2). The difference between total binding and the binding in the presence of competitor is a measure of the specific binding. BBMV from the two colonies showed specific binding, indicating that the resistance was not due to an absence of binding to the epithelial membrane. To determine whether quantitative binding parameters were significantly different between the two colonies, competition binding assays were performed (Fig. 3). Incubation of a fixed amount of 125I-Vip3Aa with increasing concentrations of unlabeled protein showed that Vip3Aa fitted a one-site curve in both the resistant and the susceptible colony. Additionally, there were no significant differences in the equilibrium dissociation constants (Kd) and the concentration of binding sites (Rt) between the two colonies (Table 3). It is worth mentioning that no specific binding could be obtained with BBMV prepared from lyophilized tissue and, therefore, this type of preparation method does not preserve the binding sites involved in Vip3Aa binding.


Characterization of the resistance to Vip3Aa in Helicoverpa armigera from Australia and the role of midgut processing and receptor binding.

Chakroun M, Banyuls N, Walsh T, Downes S, James B, Ferré J - Sci Rep (2016)

Binding of 125I-Vip3Aa to BBMV from GR (susceptible) (●, ○, solid lines) and SP85 (resistant) (◼, ◻, broken lines) colonies at increasing concentrations of BBMV.The figure is representative of two independent experiments with different batches of labeled toxin.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837340&req=5

f2: Binding of 125I-Vip3Aa to BBMV from GR (susceptible) (●, ○, solid lines) and SP85 (resistant) (◼, ◻, broken lines) colonies at increasing concentrations of BBMV.The figure is representative of two independent experiments with different batches of labeled toxin.
Mentions: Specific binding of 125I-Vip3Aa to H. armigera BBMV was shown by incubating the labeled toxin in the absence and the presence of an excess of unlabeled Vip3Aa (Fig. 2). The difference between total binding and the binding in the presence of competitor is a measure of the specific binding. BBMV from the two colonies showed specific binding, indicating that the resistance was not due to an absence of binding to the epithelial membrane. To determine whether quantitative binding parameters were significantly different between the two colonies, competition binding assays were performed (Fig. 3). Incubation of a fixed amount of 125I-Vip3Aa with increasing concentrations of unlabeled protein showed that Vip3Aa fitted a one-site curve in both the resistant and the susceptible colony. Additionally, there were no significant differences in the equilibrium dissociation constants (Kd) and the concentration of binding sites (Rt) between the two colonies (Table 3). It is worth mentioning that no specific binding could be obtained with BBMV prepared from lyophilized tissue and, therefore, this type of preparation method does not preserve the binding sites involved in Vip3Aa binding.

Bottom Line: We found that, although relatively high, the frequency of alleles for resistance to Vip3Aa in field populations of H. armigera in Australia did not increase over the past four seasons until 2014/15.Vip3Aa-resistance does not confer cross-resistance to Cry1Ac or Cry2Ab.Proteolytic conversion of Vip3Aa protoxin into the activated toxin rendered the same products, though it was significantly slower in resistant insects.

View Article: PubMed Central - PubMed

Affiliation: ERI of Biotechnology and Biomedicine (BIOTECMED), Universitat de València, 46100 Burjassot, Spain.

ABSTRACT
Crops expressing genes from Bacillus thuringiensis (Bt crops) are among the most successful technologies developed for the control of pests but the evolution of resistance to them remains a challenge. Insect resistant cotton and maize expressing the Bt Vip3Aa protein were recently commercialized, though not yet in Australia. We found that, although relatively high, the frequency of alleles for resistance to Vip3Aa in field populations of H. armigera in Australia did not increase over the past four seasons until 2014/15. Three new isofemale lines were determined to be allelic with previously isolated lines, suggesting that they belong to one common gene and this mechanism is relatively frequent. Vip3Aa-resistance does not confer cross-resistance to Cry1Ac or Cry2Ab. Vip3Aa was labeled with (125)I and used to show specific binding to H. armigera brush-border membrane vesicles (BBMV). Binding was of high affinity (Kd = 25 and 19 nM for susceptible and resistant insects, respectively) and the concentration of binding sites was high (Rt = 140 pmol/mg for both). Despite the narrow-spectrum resistance, binding of (125)I-labeled Vip3Aa to BBMV of resistant and susceptible insects was not significantly different. Proteolytic conversion of Vip3Aa protoxin into the activated toxin rendered the same products, though it was significantly slower in resistant insects.

No MeSH data available.


Related in: MedlinePlus