CYTOCHROME-P450 GENES FROM HELICOVERPA-ARMIGERA - EXPRESSION IN A PYRETHROID-SUSCEPTIBLE AND PYRETHROID-RESISTANT STRAIN

The molecular basis of metabolic resistance to pyrethroids in Helicove rpa armigera is currently under debate, Substantial indirect evidence supports a role for both esterase- and cytochrome-P450-mediated metabo lism, However, the relative roles played by these two mechanisms in fi eld-based resistance is uncertain, Our understanding of the importance of P450-mediated metabolism is hindered by the paucity of cloned gene s from this species, and the corresponding absence of data on rates of insecticide metabolism by functionally expressed P450s, To facilitate P450; gene isolation from H, armigera we used degenerate primers, in. the reverse transcriptase-polymerase chain reaction (RT-PCR) to clone P450 gene fragments from the RNA of a pyrethroid-resistant strain. He re we report the isolation of eight new P450 genes: seven from the CYP 4 family and one CYP9, One of these genes, CYP4G8, is two-fold over-ex pressed in the resistant strain, whereas the other CYP4s showed either similar or undetectable levels of expression, CYP9A3 appears to be a homolog of the putatively resistance-associated CYP9A1 of Heliothis vi rescens, However, no difference in expression between the H, armigera strains was detected, CYP6B2, a gene previously reported to be over-ex pressed in a different pyrethroid-resistant strain of H, armigera, als o revealed non-detectable levels of expression in both strains, These observations suggest that different P450s may be over-expressed in dif ferent resistant strains, and emphasize that recombinant expression wi ll be necessary in order to define precisely their individual substrat e specificities and ability to metabolize pyrethroids, The gene fragme nts described here represent an important first step in this direction , (C) 1997 Elsevier Science Ltd.