Up-Regulated Serpin Gene Involved in Cry1ac Resistance in Helicoverpa Armigera

Decreased protoxin activation because of lower enzymatic activities of trypsin and chymotrypsin was associated with resistance to Cry1Ac . Nevertheless, the mechanism of down regulated activities of trypsin and chymotrypsin in Cry1Ac resistance was poorly understood. Previously, we identified an endogenous serpin could inhibit the midgut proteases to activate Cry1Ac and reduce the insecticide activity to Helicoverpa armigera . Herein, we confirmed that proteases activities were significantly lower in Cry1Ac-resistant strain than that in susceptible strain and trypsin could enhance the toxicity of Cry1Ac to H. armigera . Although the amino acid sequence of serpin-e gene were identical between LFS susceptible and LF30 resistant strains, its relative expression in midgut was significantly higher in resistant than in susceptible strain during all developmental stages. Importantly, RNAi-mediated silencing of serpin-e gene expression improved protease activities and increased larval susceptibility to Cry1Ac protoxin in the resistant strain, supporting that high expression of serpin-e gene was involved in Cry1Ac resistance in H. armigera . These conclusions provide a new insight into understanding the role of serpin in the mechanisms underlying insect resistance to Bt toxins.