Cloning and expression of cytochrome P450 CYP6B7 in fenvalerate‐resistant and susceptible Helicoverpa armigera (Hübner) from China

Abstract

Our previous studies have found that the levels of cytochrome P450 and oxidative activities of cytochrome P450 monooxygenases were enhanced in a fenvalerate‐resistant strain (HDFR) of Helicoverpa armigera (Hübner) in China, comparing with those of a susceptible strain (HDS). Here, we report the molecular cloning and gene expression of a specific P450 CYP6B7 from HDFR and HDS strain of H. armigera. Comparison of the deduced amino acid sequence showed that there were three substitutions of amino acids in the coding region of CYP6B7 cDNA of HDFR strain, comparing with that of HDS strain. Meanwhile, there were three mutative nucleotides in the intron of CYP6B7 genomic DNA in HDFR strain. Northern blotting analysis showed that the expression of CYP6B7 mRNA in HDFR strain of H. armigera was more than 5‐fold higher than that in HDS strain. Further studies indicated that the expression of CYP6B7 mRNA increased as the larvae developed; however, it was rarely detected in the pupae and adult stages. The results suggested that cytochrome P450 CYP6B7 plays an important role in the pyrethroid insecticide fenvalerate resistance of HDFR strain of H. armigera; over‐expression of CYP6B7 combined with relevant substitution of amino acids might be responsible for fenvalerate‐resistance in H. armigera from China.

Variation in P450-mediated fenvalerate resistance levels is not correlated with CYP337B3 genotype in Chinese populations of Helicoverpa armigera

“…One of these is CYP337B3, as already discussed. One of the others, CYP6B7, has been shown to be overexpressed in fenvalerate resistant strains in both Australia [37] and China [20,23] and its role in resistance was verified by RNA interference [22]. The other two, CYP9A12 and CYP9A14, which showed much higher expression (433-and 59-fold in the fatbody and 19-and 4.3-fold in the midgut) of the Chinese resistant strain tested, were subsequently shown to be capable of metabolizing fenvalerate after heterologous expression in yeast [20,38].…”

“…In the case of H. armigera, the resistance is generally due to enhanced metabolism, and bioassays with the P450 inhibitor piperonyl butoxide (PBO) and the esterase inhibitor S,S,S-tributyl phosphorotrithioate (DEF) implicate both in the resistance but find that the relative contributions of the two classes of enzyme to resistance vary among populations [6][7][8][9][10][11]. Several individual P450s [12][13][14][15][16][17] and esterases [10,18,19] have been shown to metabolize pyrethroids and some, specifically CYP337B3, CYP6B7, CYP9A12 and CYP9A14 [20][21][22][23], and CCE001a, CCE001c, CCE001d and CCE001i [10,18,19], have also been found to be more highly expressed in resistant strains in at least one study. However quantitative trait loci (QTL) mapping has only so far directly associated one enzyme, CYP337B3, with resistance [14].…”

Resistance of AustralianHelicoverpa armigerato fenvalerate is due to the chimeric P450 enzyme CYP337B3

“…So far, all other described P450s associated with insecticide resistance are expressed in susceptible insects and overexpressed in resistant insects (16,17,29,30,39,41,42,44,45,(52)(53)(54)(55)(56)(57). Overexpression can be caused by trans-(52) or cis-acting factors, the latter often associated with transposable element insertion in the promoter region (53,58,59).…”

Cloning and characterisation of NADPH-dependent cytochrome P450 reductase gene in the cotton bollworm,Helicoverpa armigera

“…The cotton bollworm ( Helicoverpa armigera Hübner) is one of the most important polyphagous insects that may cause severe losses in a wide range of agricultural and economic crops in almost all continents . Recently, more attention has been paid to H .…”