Characterization of an Ecdysone Oxidase from (L.) and Its Role in Bt Cry1Ac Resistance.

Understanding the molecular mechanisms underlying insect resistance to (Bt) pesticidal proteins is crucial for sustainable pest management. Here, we found that downregulation of the ecdysone oxidase gene () in the normal feeding stages contributes to increased 20-hydroxyecdysone (20E) titer and mediates resistance to the Bt Cry1Ac toxin. The gene was cloned and its expression was significantly downregulated in the midgut of Bt-resistant and Cry1Ac-selected . Silencing of the gene significantly reduced Cry1Ac susceptibility, and downregulation of the gene is closely linked to Cry1Ac resistance in . The PxEO protein metabolized ecdysone (E) and 20E , and its reduction elevated 20E titers and activated the MAPK-mediated -regulatory mechanism known to directly cause the resistance phenotype. Together with our recently reported 20E-degrading glucose dehydrogenase, this finding highlights a robust, multipronged, approach developed by this insect in its 20E-mediated defense against harmful agents.