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Appl. Environ. Microbiol., Apr 1997, 1453-1459, Vol 63, No. 4
MK Lee, RM Aguda, MB Cohen, FL Gould and DH Dean
Insecticidal activity and receptor binding properties of Bacillus
thuringiensis toxins to yellow and striped rice stem borers (Sciropophaga
incertulas and Chilo suppresalis, respectively) were investigated. Yellow
stem borer (YSB) was susceptible to Cry1Aa, Cry1Ac, Cry2A, and Cry1C toxins
with similar toxicities. To striped stem borer (SSB), Cry1Ac, Cry2A, and
Cry1C were more toxic than Cry1Aa toxin. Binding assays were performed with
(sup125)I-labeled toxins (Cry1Aa, Cry1Ac, Cry2A, and Cry1C) and brush
border membrane vesicles (BBMV) prepared from YSB and SSB midguts. Both
Cry1Aa and Cry1Ac toxins showed saturable, high-affinity binding to YSB
BBMV. Cry2A and Cry1C toxins bound to YSB BBMV with relatively low binding
affinity but with high binding site concentration. To SSB, both Cry1Aa and
Cry1Ac exhibited high binding affinity, although these toxins are less
toxic than Cry1C and Cry2A. Cry1C and Cry2A toxins bound to SSB BBMV with
relatively low binding affinity but with high binding site concentration.
Heterologous competition binding assays were performed to investigate the
binding site cross-reactivity. The results showed that Cry1Aa and Cry1Ac
recognize the same binding site, which is different from the Cry2A or Cry1C
binding site in YSB and SSB. These data suggest that development of
multitoxin systems in transgenic rice with toxin combinations which
recognize different binding sites may be useful in implementing deployment
strategies that decrease the rate of pest adaptation to B. thuringiensis
toxin-expressing rice varieties.
Copyright © 1997, American Society for Microbiology
Determination of Binding of Bacillus thuringiensis (delta)-Endotoxin Receptors to Rice Stem Borer Midguts
Department of Biochemistry, The Ohio State University, Columbus, Ohio 43210; Entomology and Plant Pathology Division, International Rice Research Institute, Manila, Philippines; and Department of Entomology, North Carolina State University, Raleigh, North Carolina 27695
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