Search results for "Invertebrate Microbiology"
showing 10 items of 42 documents
Genetic and Biochemical Approach for Characterization of Resistance to Bacillus thuringiensis Toxin Cry1Ac in a Field Population of the Diamondback M…
2000
ABSTRACT Four subpopulations of a Plutella xylostella (L.) strain from Malaysia (F 4 to F 8 ) were selected with Bacillus thuringiensis subsp. kurstaki HD-1, Bacillus thuringiensis subsp. aizawai , Cry1Ab, and Cry1Ac, respectively, while a fifth subpopulation was left as unselected (UNSEL-MEL). Bioassays at F 9 found that selection with Cry1Ac, Cry1Ab, B. thuringiensis subsp. kurstaki , and B. thuringiensis subsp. aizawai gave resistance ratios of >95, 10, 7, and 3, respectively, compared with UNSEL-MEL (>10,500, 500, >100, and 26, respectively, compared with a susceptible population, ROTH). Resistance to Cry1Ac, Cry1Ab, B. thuringiensis subsp. kurstaki , and B. thuringiensis subsp…
Specific binding of Bacillus thuringiensis Cry2A insecticidal proteins to a common site in the midgut of Helicoverpa species
2008
ABSTRACT For a long time, it has been assumed that the mode of action of Cry2A toxins was unique and different from that of other three-domain Cry toxins due to their apparent nonspecific and unsaturable binding to an unlimited number of receptors. However, based on the homology of the tertiary structure among three-domain Cry toxins, similar modes of action for all of them are expected. To confirm this hypothesis, binding assays were carried out with 125 I-labeled Cry2Ab. Saturation assays showed that Cry2Ab binds in a specific and saturable manner to brush border membrane vesicles (BBMVs) of Helicoverpa armigera . Homologous-competition assays with 125 I-Cry2Ab demonstrated that this toxi…
Lack of Cry1Fa binding to the midgut brush border membrane in a resistant colony of Plutella xylostella moths with a mutaton in the ABCC2 locus
2012
ABSTRACT Previous studies reported “mode 1” Bacillus thuringiensis resistance in a colony of diamondback moths (NO-QA), and recently, this resistance has been mapped to an ABC transporter ( ABCC2 ) locus. We report the lack of binding of Cry1Fa to insects derived from this colony and compare our data with those from other insects with ABCC2 -associated resistance.
Interaction of Bacillus thuringiensis Cry1 and Vip3A Proteins with Spodoptera frugiperda Midgut Binding Sites
2009
ABSTRACT Vip3Aa, Vip3Af, Cry1Ab, and Cry1Fa were tested for their toxicities and binding interactions. Vip3A proteins were more toxic than Cry1 proteins. Binding assays showed independent specific binding sites for Cry1 and Vip3A proteins. Cry1Ab and Cry1Fa competed for the same binding sites, whereas Vip3Aa competed for those of Vip3Af.
Specific binding of radiolabeled Cry1Fa insecticidal protein from Bacillus thuringiensis to midgut sites in lepidopteran species
2012
ABSTRACT Cry1Fa insecticidal protein was successfully radiolabeled with 125 I-Na. Specific binding to brush border membrane vesicles was shown for the lepidopteran species Ostrinia nubilalis , Spodoptera frugiperda , Spodoptera exigua , Helicoverpa armigera , Heliothis virescens , and Plutella xylostella . Homologous competition assays were performed to obtain equilibrium binding parameters ( K d [dissociation constant] and R t [concentration of binding sites]) for these six insect species.
Development and Characterization of Diamondback Moth Resistance to Transgenic Broccoli Expressing High Levels of Cry1C
2000
ABSTRACT A field-collected colony of the diamondback moth, Plutella xylostella , had 31-fold resistance to Cry1C protoxin of Bacillus thuringiensis . After 24 generations of selection with Cry1C protoxin and transgenic broccoli expressing a Cry1C protein, the resistance that developed was high enough that neonates of the resistant strain could complete their entire life cycle on transgenic broccoli expressing high levels of Cry1C. After 26 generations of selection, the resistance ratios of this strain to Cry1C protoxin were 12,400- and 63,100-fold, respectively, for the neonates and second instars by a leaf dip assay. The resistance remained stable until generation 38 (G38) under continuous…
Association of Cry1Ac toxin resistance in Helicoverpa zea (Boddie) with increased alkaline phosphatase levels in the midgut lumen.
2012
ABSTRACT Resistance to Bacillus thuringiensis Cry1Ac toxin was characterized in a population of Helicoverpa zea larvae previously shown not to have an alteration in toxin binding as the primary resistance mechanism to this toxin. Cry1Ac-selected larvae (AR1) were resistant to protoxins and toxins of Cry1Ab, Cry1Ac, and the corresponding modified proteins lacking helix α-1 (Cry1AbMod and Cry1AcMod). When comparing brush border membrane vesicles (BBMVs) prepared from susceptible (LC) and AR1 larval midguts, there were only negligible differences in overall Cry1Ac toxin binding, though AR1 had 18% reversible binding, in contrast to LC, in which all binding was irreversible. However, no differe…
In Vivo and In Vitro Binding of Vip3Aa to Spodoptera frugiperda Midgut and Characterization of Binding Sites by 125 I Radiolabeling
2014
ABSTRACT Bacillus thuringiensis vegetative insecticidal proteins (Vip3A) have been recently introduced in important crops as a strategy to delay the emerging resistance to the existing Cry toxins. The mode of action of Vip3A proteins has been studied in Spodoptera frugiperda with the aim of characterizing their binding to the insect midgut. Immunofluorescence histological localization of Vip3Aa in the midgut of intoxicated larvae showed that Vip3Aa bound to the brush border membrane along the entire apical surface. The presence of fluorescence in the cytoplasm of epithelial cells seems to suggest internalization of Vip3Aa or a fragment of it. Successful radiolabeling and optimization of the…
Bacillus thuringiensis Cry1Ac Toxin-Binding and Pore-Forming Activity in Brush Border Membrane Vesicles Prepared from Anterior and Posterior Midgut R…
2008
ABSTRACT It is generally accepted that Bacillus thuringiensis Cry toxins insert into the apical membrane of the larval midgut after binding to specific receptors, and there is evidence that the distribution of binding molecules along the midgut is not uniform. By use of the voltage-sensitive dye DiSC 3 (5) and 125 I-labeled Cry1Ac, we have measured the effect of Cry1Ac in terms of permeabilization capacity and of binding parameters on brush border membrane vesicles (BBMV) prepared from the anterior and the posterior regions of the larval midgut from two insect species, Manduca sexta and Helicoverpa armigera . The permeabilizing activity was significantly higher with BBMV from the posterior …
Toxicity and mode of action of Bacillus thuringiensis Cry proteins in the Mediterranean corn borer, Sesamia nonagrioides (Lefebvre)
2006
ABSTRACT Sesamia nonagrioides is one of the most damaging pests of corn in Spain and other Mediterranean countries. Bt corn expressing the Bacillus thuringiensis Cry1Ab toxin is being grown on about 58,000 ha in Spain. Here we studied the mode of action of this Cry protein on S. nonagrioides (binding to specific receptors, stability of binding, and pore formation) and the modes of action of other Cry proteins that were found to be active in this work (Cry1Ac, Cry1Ca, and Cry1Fa). Binding assays were performed with 125 I- or biotin-labeled toxins and larval brush border membrane vesicles (BBMV). Competition experiments indicated that these toxins bind specifically and that Cry1Aa, Cry1Ab, an…