Cytochromes P450 are both induced by and metabolize furanocoumarins, a class of toxic plant allelochemicals found in the hostplants of Papilio caterpillars. Papilio glaucus, the Eastern tiger swallowtail, is a generalist within the genus and rarely encounters furanocoumarins in its diet. CYP6B4, a cytochrome P450 gene isolated from its midgut, is constitutively expressed at negligible levels but is highly induced in the presence of xanthotoxin, a linear furanocoumarin. The promoter of CYP6B4 contains a xenobiotic response element to xanthotoxin (XRE-Xan) that activates xanthotoxin-inducible transcription of CYP6B1, a gene isolated from Papilio polyxenes, a specialist on furanocoumarin-containing plants. We transfected insect Sf9 cells with reporter plasmids that contain varying lengths of the CYP6B4 promoter, with and without XRE-Xan, fused to the reporter gene chloramphenicol acetyl transferase (CAT). We then treated cells with xanthotoxin in methanol(1 ug/ul) and methanol alone and measured changes in CAT activity. For comparison, we also transfected cells with a region of the CYP6B1 promoter that contains XRE-Xan. Relative CAT activity was signficantly induced by xanthotoxin when XRE-xan was present in the promoter of CYP6B4, but activity was signicantly lower for CYP6B4 than CYP6B1. Differences in transcriptional regulation of CYP6B4 and CYP6B1 reflect the breadth of diets that P. glaucus and P. polyxenes utilize in nature and suggest a molecular mechanism for the expansion of host range observed in Papilio butterflies.
Species 1: Lepidoptera Papilionidae Papilio glaucus (Eastern tiger swallowtail)
Keywords: coevolution, transcription
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