Spontaneous transposition of HzSINE1 into CYP321A2 is undetectable in the field populations of Helicoverpa zea

The enrichment of transposable elements (TEs) within allelochemical- and insecticide-metabolizing P450 alleles in Helicoverpa zea enables these P450s to gain TE-introduced adaptive variations otherwise not readily available to cope with the ever-changing and diverse xenobiotic stress factors in varying cropping systems. The critical role of each TE-inserted P450 allele depends on whether the inserted P450 allele is more adaptive than its TE-free counterpart or not. Previous study has reported a HzSINE1-inserted CYP321A2 allele in a laboratory strain of H. zea reared with xenobiotic-free artificial diets. Here we show that the HzSINE1-inserted CYP321A2 allele transcribes into two HzSINE1 sequence-containing mutant mRNA isoforms of different length that encode an identical C terminus-truncated and heme-binding region deleted non-functional P450. Nonetheless, HzSINE1 insertion does not disrupt the regulatory functional aspect of CYP321A2 since this allele is constitutively expressed and highly inducible by the allelochemicals xanthotoxin, quercetin and chlorogenic acid. Furthermore, while the HzSINE1-inserted CYP321A2 allele is fixed in the laboratory strain, the insertion is purged in the bifenthrin-resistant strain and the Georgia field population of H. zea. To sum up, the HzSINE1-inserted CYP321A2 allele represents an allelochemical-inducible non-functional P450 allele that is selected against in the field populations frequently encountering toxic plant allelochemicals and synthetic insecticides. However, such an insertion can reach fixation under the xenobiotic-free laboratory rearing conditions most likely due to random genetic drift across multiple generations.