A cytochrome P450 from juvenile mustard leaf beetles hydroxylates geraniol, a key step in iridoid biosynthesis

Abstract

AbstractJuveniles of the leaf beetle Phaedon cochleariae synthesize iridoid via the mevalonate pathway to repel predators. The normal terpenoid biosynthesis is integrated into the dedicated defensive pathway by the ω-hydroxylation of geraniol to 8-hydroxygeraniol. Here we identify and characterize the geraniol 8-hydroxylase as a P450 monooxygenase using integrated transcriptomic and proteomic analyses. In the fat body, 73 individual cytochrome P450s were identified. The double stranded RNA (dsRNA)-mediated knock down of CYP6BH5 led to a significant reduction of 8-hydroxygeraniol-glucoside in the hemolymph and, later, of the chrysomelidial in the defensive secretion. Heterologously expressed CYP6BH5 converted geraniol to 8-hydroxygeraniol. In addition to geraniol, CYP6BH5 also catalyzes other monoterpenols, such as nerol and citronellol, into the corresponding α, ω-dihydroxy compounds.HighlightsThe geraniol 8-hydroxylase in Phaedon cochleariae was identified as a cytochrome P450 CYP6BH5.RNA interference emphasized the importance of CYP6BH5 in iridoid biosynthesis.In vitro enzyme assays showed that recombinant CYP6BH5 is a substrate promiscuous enzyme, converting the ω-hydroxylation of geraniol, nerol, citronellol but not linalool.Homology modeling suggested the -OH group of the substrate plays an important role in coordinating the substrates with the enzyme’s catalytic cavity.