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Appl. Environ. Microbiol., 11 1995, 3836-3842, Vol 61, No. 11
MK Lee, F Rajamohan, F Gould and DH Dean
The Bacillus thuringiensis toxin-binding properties of midgut epithelial
cells from two strains of Heliothis virescens were compared. One H.
virescens strains (YHD2) which was selected against CryIAc toxin had over
10,000-fold resistance to CryIAc toxin relative to the susceptible strain
and was cross-resistant to CryIAa and CryIAb. The second H. virescens
strain (YDK) was susceptible to these toxins in the order CryIAc >
CryIAb > CryIAa. Receptor-binding properties of CryIAa, CryIAb, and
CryIAc toxins were compared between the susceptible and resistant strains.
Saturation and competition-binding experiments were performed with brush
border membrane vesicles prepared from midguts of the susceptible and
resistant insects and 125I-labeled toxins. In the susceptible strain,
saturable, specific, and high-affinity binding of all three toxins was
observed. The relative binding-site concentration was directly correlated
with toxicity (CryIAc > CryIAb > CryIAa). In the resistant strains,
the binding affinities of CryIAb and CryIAc were similar to that observed
with the susceptible strain and ony minor differences in binding-site
concentration (Bmax) were observed. The major difference between the two
strains was the total lack of binding of CryIAa toxin to the brush border
membrane vesicles of the resistant strain. Heterologous competition-binding
experiments and ligand blot analysis supported the hypothesis that there
were multiple binding sites for the toxins. On the basis of results of the
present study, we propose that alterations in binding proteins shared by
all three toxins are a major factor in resistance. This suggests that not
all receptors of CryIAc might be involved in toxic function.
Copyright © 1995, American Society for Microbiology
Resistance to Bacillus thuringiensis CryIA delta-endotoxins in a laboratory-selected Heliothis virescens strain is related to receptor alteration
Department of Biochemistry, Ohio State University Columbus 43210, USA.
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