Abstract
Cry toxins produced by the bacterium Bacillus thuringiensis are effective biological insecticides. Cadherin-like proteins have been reported as functional Cry1A toxin receptors in Lepidoptera. Here we present data that demonstrate that a coleopteran cadherin is a functional Cry3Aa toxin receptor. The Cry3Aa receptor cadherin was cloned from Tenebrio molitor larval midgut mRNA, and the predicted protein, TmCad1, has domain structure and a putative toxin binding region similar to those in lepidopteran cadherin B. thuringiensis receptors. A peptide containing the putative toxin binding region from TmCad1 bound specifically to Cry3Aa and promoted the formation of Cry3Aa toxin oligomers, proposed to be mediators of toxicity in lepidopterans. Injection of TmCad1-specific double-stranded RNA into T. molitor larvae resulted in knockdown of the TmCad1 transcript and conferred resistance to Cry3Aa toxicity. These data demonstrate the functional role of TmCad1 as a Cry3Aa receptor in T. molitor and reveal similarities between the mode of action of Cry toxins in Lepidoptera and Coleoptera.
Highlights
Cry toxins produced by the bacterium Bacillus thuringiensis are effective biological insecticides
The Cry3Aa receptor cadherin was cloned from Tenebrio molitor larval midgut mRNA, and the predicted protein, TmCad1, has domain structure and a putative toxin binding region similar to those in lepidopteran cadherin B. thuringiensis receptors
A partial D. virgifera virgifera cadherin fragment corresponding to cadherin repeat (CR) domains 8 –10 was reported to bind activated Cry3Aa and Cry3Bb toxins and enhance toxin activity in several beetles, suggesting that cadherin plays a functional role in B. thuringiensis intoxication in beetles [29]
Summary
377–404 883–909 1023–1044 Adapter 4526–4548 1982–2001 2454–2473 1982–2001 2215–2234 401–420 567–584. The high degree of structural similarity among Cry1, -2, -3, and -4 toxins implies that they share a similar mode of action in insects [2, 31] To test this hypothesis, we evaluated whether a cadherin in the midgut of a B. thuringiensis-sensitive coleopteran is a functional receptor for coleopteran-specific Cry3Aa toxin. We demonstrate that reduced levels of the TmCad (T. molitor cadherin) transcript in actively feeding larvae correlate with a reduction in Cry3Aa toxicity. These results support the hypothesis that T. molitor cadherin is a functional Cry3Aa receptor analogous to lepidopteran cadherin receptors and highlight a common interface for Cry toxins in two major insect orders
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