Recombinant Botryotinia fuckeliana Presilphiperfolan-8-beta-ol synthase (BOT2)

Presilphiperfolan-8-beta-ol synthase; part of the gene cluster that mediates the biosynthesis of botrydial. Botrydial is necessary for colonization of plant tissue by the T4 strain. It is a strain-dependent virulence factor since highly aggressive strains like SAS56 or B05 still retain substantial virulence when botrydial synthesis is impaired, since they produce also botcinic acid. The first step of botrydial biosynthesis is performed by the sesquiterpene synthase BOT2 which catalyzes the cyclization of farnesyl diphosphate (FPP) to presilphiperfolan-8-beta-ol (PSP). The cytochrome P450 monooxygenase BOT4 then catalyzes the hydroxylation at C-4 to give a probotryane intermediate. Acetylation of the hydroxyl at C-4 is carried out by the acetyltransferase BOT5, followed by the combined action of the P450 monooxygenases BOT3 and BOT1, to yield finally the glycol, via the regio- and stereospecific hydroxylations at C-10 and C-15 of the probotryane intermediates, respectively. The cleavage of the C10-C15 bond of probotryane skeleton is an intriguing and chemically important reaction, which could be mediated by some of the monooxygenases or by a combination of them. It is possible that either BOT3 or BOT1 would oxidize either the 10- or the 15-hydroxy group to the hydroperoxide derivative, which would then undergo heterolytic fragmentation to give the dialdehyde botrydial. Finally, the dehydrogenase BOT7 might be involved in the conversion of botrydial to dihydrobotrydial.