Down-Regulation of eIF3L Is Associated with Decreased Susceptibility of Helicoverpa armigera to Cry1Ac

Large-scale cultivation of transgenic Bt crops has led to target pest resistance to Bt proteins, especially Cry1Ac. Under persistent selection pressure, Helicoverpa armigera has evolved resistance to Bt proteins in both laboratory and field populations, highlighting an urgent need to comprehensively elucidate the molecular mechanisms underlying pest Bt resistance. Previous studies have confirmed that the eukaryotic translation initiation factor eIF2 plays a critical role in regulating Bt resistance. Our prior RNA-seq data showed significant differences in the expression level of eIF3L between susceptible and Cry1Ac-resistant strains of H. armigera. In this study, we further observed that the mRNA level of eIF3L was significantly reduced in larvae surviving Cry1Ac exposure. More importantly, heterologous expression of eIF3L increased the susceptibility of Sf9 cells to Cry1Ac. Consistently, knockdown of eIF3L was associated with reduced mortality in H. armigera larvae exposed to Cry1Ac. Together, our in vivo and in vitro results suggest that eIF3L is involved in Cry1Ac toxicity. Furthermore, eIF3L affects the expression of the Cry1Ac receptor genes CAD, ABCC2, and ABCC3. Collectively, these results indicate that down-regulation of eIF3L is associated with decreased susceptibility of H. armigera to Cry1Ac, providing novel insights into the molecular mechanisms underlying insect resistance to Bt proteins.