A cadherin‐like protein influences B acillus thuringiensis   Cry 1 Ab toxicity in the oriental armyworm, M ythimna separata

Cadherins comprise a family of calcium‐dependent cell adhesion proteins that act in cell–cell interactions. Cadherin‐like proteins ( CADs ) in midguts of some insects act as receptors that bind some of the toxins produced by the B acillus thuringiensis ( Bt ). We cloned a CAD gene associated with larval midguts prepared from M ythimna separata . The full‐length cDNA ( MsCAD1 , G en B ank Accession No. JF 951432) is 5642 bp, with an open reading frame encoding a 1757 amino acid and characteristics typical of insect CADs . Expression of MsCAD1 is predominantly in midgut tissue, with highest expression in the 3rd‐ to 6th‐instars and lowest in newly hatched larvae. Knocking‐down MsCAD1 decreased Cry 1 Ab susceptibility, indicated by reduced developmental time, increased larval weight and reduced larval mortality. We expressed MsCAD1 in E . coli and recovered the recombinant protein, rMsCAD 1, which binds Cry 1 Ab toxin. Truncation analysis and binding experiments revealed that a contiguous 209‐aa, located in CR 11 and CR 12, is the minimal Cry 1 Ab binding region. These results demonstrate that MsCAD 1 is associated with Cry 1 Ab toxicity and is one of the Cry 1 Ab receptors in this insect. The significance of this work lies in identifying MsCAD 1 as a Cry 1 Ab receptor, which helps understand the mechanism of Cry 1 Ab toxicity and of potential resistance to Bt in M . separata .