The first cytochrome P450 in ferns: Evidence for its involvement in phytoecdysteroid biosynthesis in Polypodium vulgare

The fern Polypodium vulgare is a phytoecdysteroid (PE)-producing plant. Cultures of P. vulgare prothalus produce PE, whereas prothalus-derived callus cultures do not. However, this callus line can transform topically applied ecdysone (E) to 20-hydroxyecdysone (20E), which is the last step in the biosynthetic pathway of the main plant PE. This hydroxylation is catalysed by a cytochrome P450 enzyme. E treatment of the callus line results in an increased amount of P450, showing a linear correspondence between the amount of P450 and in vivo E 20-hydroxylation activity, estimated by measuring the bioconversion of E to 20E. This activity can be inhibited by molecules that bind to the P450-heme group. E shows a P450-substrate-binding spectrum with microsomes that overexpress the P450 protein. Finally, a P450 protein was purified from E-treated calli, this being the first P450 to be described in the pterydophyte group.