Identification of permethrin-inducible cytochrome P450s from the diamondback moth, Plutella xylostella (L.) and the possibility of involvement in permethrin resistance

Insect cytochrome P450 monooxygenases (P450s) are important enzymes involved in catalysis of many reactions leading to insecticide resistance. In this study, a PCR (polymerase chain reaction) technology using degenerate primers based on conserved P450 heme-binding region was employed to identify P450 cDNA sequences in a laboratory strain of the diamondback moth, Plutella xylostella (L.), which might have roles in permethrin resistance. Six distinct P450 cDNA sequences were isolated and were classified under CYP4 and CYP6 families. Real time RT-PCR analysis revealed that two of the cDNA clones, CYP6BG1 and CYP6BG2, were found overexpressed (4.9- and 3.8-fold, respectively) in fourth (last) instars of the resistant compared to the susceptible strain. The observed overexpression suggests potential implication in permethrin resistance. Since the phenomenon of P450 induction is also thought to contribute to resistance development, inducibility of the isolated P450s at the transcript level, specifically the overexpressed ones were analyzed and correlated with permethrin toxicity. Real time RT-PCR revealed significant induction of CYP6BG1 and CYP6BF1v4 in susceptible strains, but bioassay showed an insignificant decrease in permethrin toxicity to induced larvae.