SlGSTE8 in Spodoptera litura participated in the resistance to phoxim and chlorpyrifos

Glutathione S-transferases (GSTs) were reported to participate in
insecticides resistance by metabolic and antioxidant activities. In our
previous study, an ε class gene of GSTs, SlGSTe8 in Spodoptera litura, was
screened out to be upregulated in a population resistant to pyrethroids
and organophosphates. SlGSTe8 was highly expressed in the larvae stage,
and the digestive tissue, foregut, midgut and hindgut. While the relative
expression level was low in the pupae stage and other tissues. To further
explore its role in the resistance to pyrethroids and organophosphates,
the metabolic activity to insecticides by its recombinant protein was
determined by Ultra Performance Liquid Chromatography, and its antioxidant
enzyme activity was evaluated by disc diffusion assay. The recombinant
protein showed significantly metabolic activity to phoxim and
chlorpyrifos, but not to fenvalerate, cyhalothrin or β-cypermethrin. After
incubation, the depletion rate of chlorpyrifos is 85.3%, higher than that
of phoxim (17.5%). Also, the inhibition zone around filter discs decreased
significantly after exposure to cumene hydroperoxide in recombinant
plasmid than vector only, suggesting significant antioxidant activity of
SlGSTE8. Further modeling and docking analysis indicated that the 3D
structure of SlGSTE8 were well shaped for phoxim and chlorpyrifos, with
the binding energy -5.58 and -5.15 kcal/mol, respectively. Our work
provides evidence that SlGSTe8 in S. litura plays important roles in
phoxim and chlorpyrifos resistance.