Myrothecium roridum Tri4 encodes a multifunctional oxygenase required for three oxygenation steps

The biosyntheses of both macrocyclic trichothecenes in Myrothecium roridum and simple trichothecenes in Fusarium species begin with the cyclization of farnesyl pyrophosphate to form the sesquiterpene hydrocarbon trichodiene. A previous study showed that Myrothecium has a cluster of 3 genes that are homologous with Fusarium trichothecene genes: Tri4, a P450 oxygenase; Tri5, the sesquiterpene cyclase; and Tri6, a zinc-finger regulatory gene. Fusarium graminearum Tri4 (FgTri4) and M. roridum MrTri4 (MrTri4) have 66.9% identity. In this study, MrTri4 was expressed in Fusarium verticillioides. Liquid cultures of transformant strains expressing MrTri4 converted exogenous trichodiene to isotrichodiol, indicating that MrTri4 controls 3 oxygenation steps and that the product of MrTRI4 is isotrichodiol.