CYP6B3: a second furanocoumarin-inducible cytochrome P450 expressed in Papilio polyxenes

Cytochrome P450 monooxygenases in the larvae of Papilio polyxenes (black swallowtail) (Lepidoptera: Papilionidae) are capable of detoxifying linear and angular furanocoumarins found in their host plants. The CYP6B1 locus, which is transcriptionally induced in these larvae in response to xanthotoxin, encodes a P450 that principally metabolizes linear furanocoumarins such as xanthotoxin and bergapten. We have now cloned CYP6B3 cDNA derived from a second locus that is evolutionarily related to the CYP6B1 locus. Reverse transcription-PCR Southern analyses have demonstrated that CYP6B3 transcripts are expressed in response to a wider range of linear and angular furanocoumarins but at lower abundance than CYP6B1 transcripts. Whereas CYP6B1 transcripts are expressed at a low detectable level in uninduced control larvae and at high levels in xanthotoxin-induced larvae, CYP6B3 transcripts are nearly undetectable in control larvae and are highly induced by xanthotoxin and bergapten (linear furanocoumarins) as well as by angelicin and sphondin (angular furanocoumarins). The fact that these two CYP6B loci are differentially regulated by these four furanocoumarins indicates that P. polyxenes has adapted to the presence of the wide range of furanocoumarins in its host plants by diversifying its P450 isozyme structure and its furanocoumarin-responsive regulatory cascades.