APN3 Acts as a Functional Receptor of <i>Bacillus thuringiensis</i> Cry1Ac in <i>Grapholita molesta</i>

<i>Grapholita molesta</i> (Busck) (<i>Lepidoptera</i>: <i>Tortricidae</i>) is a worldwide <i>Rosaceae</i> fruit tree pest. Although the <i>Bacillus thuringiensis</i> (Bt) Cry1Ac proteins exhibit excellent insecticidal activity against <i>G. molesta</i>, there are no reported Bt receptors for <i>G. molesta</i>. In the preliminary screening, we identified <i>aminopeptidase N3</i> (<i>GmolAPN3</i>) as a potential receptor for Cry1Ac in <i>G. molesta</i>. Ligand blot and homologous competition experiments confirmed the simultaneous binding of interaction domains 2 (GluZincin superfamily domain) and 4 (ERAP1-C domain) of GmolAPN3 to activated Cry1Ac. In the cell toxicity bioassay, the overexpression of GmolAPN3 rendered Sf9 cells more susceptible to activated Cry1Ac. The results from dsRNA interference demonstrated that knockdown of <i>GmolAPN3</i> conferred resistance in <i>G. molesta</i> larvae against Cry1Ac. Our findings provide pioneering evidence for the role of GmolAPN3 as the first identified Bt receptor mediating both binding and toxicity of Cry1Ac in <i>G. molesta</i> and also offer theoretical guidance for understanding the mode of action of Cry1Ac in <i>G. molesta</i> and its field applications.