Imidacloprid is hydroxylated by Laodelphax striatellus CYP6AY3v2.

Laodelphax striatellus (Fallén) is one of the most destructive pests of rice, and has developed high resistance to imidacloprid. Our previous work indicated a strong association between imidacloprid resistance and the overexpression of a cytochrome P450 gene CYP6AY3v2 in a L. striatellus imidacloprid resistant strain (Imid-R). In this study, a transgenic Drosophila melanogaster line that overexpressed the L. striatellus CYP6AY3v2 gene was established and was found to confer increased levels of imidacloprid resistance. Furthermore, CYP6AY3v2 was co-expressed with D. melanogaster cytochrome P450 reductase (CPR) in Spodoptera frugiperda 9 (SF9) cells. A carbon monoxide difference spectra analysis indicated that CYP6AY3v2 was expressed predominately in its cytochrome P450 (P450) form, which is indicative of a good-quality functional enzyme. The recombinant CYP6AY3v2 protein efficiently catalysed the model substrate P-nitroanisole to p-nitrophenol with a maximum velocity (Vmax ) of 60.78 ± 3.93 optical density (mOD)/min/mg protein. In addition, imidacloprid itself was metabolized by the recombinant CYP6AY3v2/nicotinamide adenine dinucleotide 2'-phosphate reduced tetrasodium salt (NADPH) CPR microsomes in in vitro assays (catalytic constant (Kcat ) = 0.34 pmol/min/pmol P450, michaelis constant (Km ) = 41.98 μM), and imidacloprid depletion and metabolite peak formation were with a time dependence. The data provided direct evidence that CYP6AY3v2 is capable of hydroxylation of imidacloprid and conferring metabolic resistance in L. striatellus.

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