Functional Analysis of Odorant-Degrading Enzymes Responding to the Repellent Activity of 2,3-Dimethyl-6-(1-Hydroxy)-Pyrazine Against Plutella xylostella

Plutella xylostella is an important cruciferous crop pest with critical resistance to many chemical insecticides; 2,3-dimethyl-6-(1-hydroxy)-pyrazine has shown obvious repellent activity against P. xylostella with significant effects on the olfactory system. Here, we obtained 55 different expressions ODE (odorant-degrading enzyme) genes from the antennae of P. xylostella for 2,3-dimethyl-6-(1-hydroxy)-pyrazine treatment using RNA-seq. Three candidate PxylODEs were identified using RT-qPCR: PxylCYP9f2, PxylGSTe1, and PxylGSTs1. They each had log2-fold change values of 0.67, 2.39, and 2.08, respectively. PxylGSTs1 had a significant expression level in the antennae of P. xylostella adults, where the content in males was 3.60-fold higher than in females. Moreover, the binding style between PxylODEs and pyrazine was mainly hydrophobic, and the binding energy was −5.82 kcal mol−1 of PxylGSTs1, determined using molecular dynamics and docking. Finally, PxylGSTS1 was calculated to have a higher binding affinity to pyrazine with a Ki value of 11.63 μmol L−1 according to a fluorescence competitive binding experiment, which was validated with mutations of the TYR7 side chain. These findings illustrate that PxylGSTS1 plays an important role in the response to 2,3-dimethyl-6-(1-hydroxy)-pyrazine, which can be used in the green control of P. xylostella and other Lepidopteran pests in the field.