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Functional characterization of Bacillus thuringiensis Cry toxin receptors explains resistance in insects

Shiho Tanaka1, Haruka Endo1, Satomi Adegawa1

  • 1Graduate School of Bio-Applications and Systems Engineering, Tokyo University of Agriculture and Technology, Japan.

The FEBS Journal
|November 5, 2016
PubMed

Insights

Bacillus thuringiensis Cry toxins form pores with insect receptors. Bombyx mori ABC transporter C2 (BmABCC2) and cadherin-like receptor (BtR175-TBR) synergistically enhance Cry1Aa pore formation, crucial for insecticide activity.

Area of Science:

  • Molecular Biology
  • Insect Toxicology
  • Biochemistry

Background:

  • Bacillus thuringiensis Cry toxins are vital insecticides used in agriculture.
  • The precise mechanisms of Cry toxin receptor binding, specificity, and activity remain largely uncharacterized.
  • Understanding these interactions is key to developing effective pest control strategies.

Purpose of the Study:

  • To investigate the functional roles of Bombyx mori ABC transporter C2 (BmABCC2), BtR175-TBR, and BmAPN1 in Cry1Aa toxin-mediated pore formation.
  • To elucidate the synergistic effects between different Cry toxin receptors on pore formation activity.
  • To determine the contribution of specific receptors to insect resistance against Cry toxins.

Main Methods:

  • cRNAs encoding BmABCC2, BtR175-TBR, or BmAPN1 were injected into Xenopus oocytes.
  • Cry1Aa-dependent cation-selective pore formation was analyzed using two-electrode voltage clamp electrophysiology.
  • Toxin-receptor interactions and oligomerization were assessed in oocytes expressing single or multiple receptors.

Main Results:

  • BmABCC2 expression facilitated rapid, stable Cry1Aa-induced cation-selective pore formation.
  • BtR175-TBR alone did not induce significant pore formation, suggesting limited toxin entry.
  • Co-expression of BtR175-TBR and BmABCC2 showed a synergistic effect on Cry1Aa pore formation at lower toxin concentrations.
  • BmAPN1 bound Cry1Aa but did not mediate pore formation independently.

Conclusions:

  • BmABCC2 is crucial for Cry1Aa pore formation, while BtR175-TBR modulates this activity synergistically.
  • The synergistic interaction between BmABCC2 and BtR175-TBR is essential for efficient Cry1Aa pore formation and insecticidal activity.
  • Absence of synergistic receptor interactions, like in insects lacking BtR175-TBR but expressing BmABCC2, contributes to moderate Cry toxin resistance.
Keywords:
Bacillus thuringiensisBombyx moriABC transporter C2cadherin-like receptortwo-electrode voltage clamp

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