Constitutive Overexpression of Multiple Cytochrome P450 Genes Associated with Pyrethroid Resistance in Helicoverpa armigera

Abstract

Our previous studies showed that enhanced cytochrome P450-mediated detoxification is a major mechanism responsible for pyrethroid resistance in a laboratory-selected strain (YGF) of Helicoverpa armigera (Hübner). Two new cytochrome P450 genes, CYP9A12 and CYP9A14 (encoding 531 and 530 amino acid residues, respectively) were isolated from the fat body of the YGF strain of H. armigera. The mRNA expression levels of these two CYP9 P450 genes, together with CYP6B7 and CYP4G8 (previously reported to be overexpressed in pyrethroid-resistant strains), were assessed by real-time quantitative reverse transcription-polymerase chain reaction in the final instars of a field-derived YG strain (with seven-fold resistance to the pyrethroid fenvalerate) and the YGF strain (selected from the YG strain with fenvalerate in the laboratory, with 1,690-fold resistance to fenvalerate). The mRNA expression levels of CYP9A12, CYP9A14, and CYP6B7 in the fat body of the YGF strain increased to 433-, 59-, and 9.3-fold, respectively, compared with the YG strain, whereas no overexpression was revealed for CYP4G8. CYP9A12 and CYP9A14 had 19- and 4.3-fold overexpression in the midgut of the YGF strain compared with the YG strain, respectively, but CYP6B7 and CYP4G8 were not overexpressed. The current study provided evidence that constitutive overexpression of multiple cytochrome P450 genes (CYP9A12, CYP9A14, and CYP6B7) is associated with pyrethroid resistance in H. armigera.

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).…”

Transposable elements are enriched within or in close proximity to xenobiotic-metabolizing cytochrome P450 genes

“…Multiple P450 genes exist in a given genome, some of which may function as essential housekeeping genes involved in the biosynthesis of hormones [18,19]; others may act as environmental response genes involved in the biosynthesis of toxic compounds for plant defense or pathogens attack or in the detoxification of naturally-occurring and synthetic xenobiotics [2,17,20]. To address the issue of whether TEs mediate genomic changes in the environmental response P450 genes, we scanned two alleles (one from a laboratory colony, another from a cell line) per each of the six xenobiotic-metabolizing Helicoverpa zea P450 genes, CYP6B8, CYP6B27, CYP9A12v3, CYP9A14, CYP321A1 and CYP321A2 [21][22][23][24][25], for the presence of TE insertions by genome walking and sequence analysis. Twelve novel TEs, including LINEs (long interspersed nuclear elements), SINEs (short interspersed nuclear elements), MITEs (miniature inverted-repeat transposable elements), one fulllength transib-like transposon, and one full-length Tcllike DNA transpson, are identified from their introns, exons or flanking regions.…”

“…Two cDNA sequences representing CYP9A12 and CYP9A14 were isolated from a pyrethroid-resistant strain of Helicoverpa armigera [25], the old world sibling species of H. zea. The fact that the CYP9A12 and CYP9A14 transcripts in the pyrethroid-selected resistant strain are overexpressed 433-and 59-fold in the fatbody and 19-and 4.3-fold in the midgut, respectively, in comparison with the unselected parental strain, indicates that these two P450s are associated with pyrethroid resistance [25].…”

Characterization of Drosophila melanogaster cytochrome P450 genes

“…For example, CYP6B1v1 and CYP6B3v1 from the black swallowtail butterfly, Papilio polyxenes, can metabolize the furanocoumarins it is exposed to in its diet (32,33). Numerous individual P450s have also been implicated in insecticide resistance in different insect populations (34)(35)(36)(37)(38).…”