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

Understanding the molecular mechanisms underlying insect resistance to Bacillus thuringiensis (Bt) pesticidal proteins is crucial for sustainable pest management. Here, we found that downregulation of the Plutella xylostella ecdysone oxidase gene (PxEO) in the normal feeding stages contributes to increased 20-hydroxyecdysone (20E) titer and mediates resistance to the Bt Cry1Ac toxin. The PxEO gene was cloned and its expression was significantly downregulated in the midgut of Bt-resistant and Cry1Ac-selected P. xylostella. Silencing of the PxEO gene significantly reduced Cry1Ac susceptibility, and downregulation of the PxEO gene is closely linked to Cry1Ac resistance in P. xylostella. The PxEO protein metabolized ecdysone (E) and 20E in vitro, and its reduction elevated 20E titers and activated the MAPK-mediated trans-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.