Submitted to: Canadian Journal of Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/25/2007
Publication Date: 5/1/2007
Citation: Mc Cormick, S.P., Alexander, N.J. 2007. Myrothecium roridum Tri4 encodes a multifunctional oxygenase required for three oxygenation steps. Canadian Journal of Microbiology. 53:572-579. Interpretive Summary: The mold Myrothecium roridum causes diseases of melons and tomatoes. This mold makes macrocyclic trichothecene mycotoxins that are a hazard to human health. Trichothecenes are protein synthesis inhibitors but the unique structural features of macrocyclic trichothecenes make them 10 fold more toxic than Fusarium trichothecenes. In Fusarium, a group of fifteen well characterized genes controls the production of the toxins. In this report, we focus on a Myrothecium gene (Tri4) that begins the process of making a toxic compound by adding oxygens to a non toxic hydrocarbon backbone. When this gene is knocked out, the fungus cannot make toxins. We transferred Tri4 from Myrothecium into another fungus, Fusarium verticillioides, and found that this gene controlled three steps, including the addition of the epoxide group required for toxicity. A better understanding of this early toxin gene is of interest to researchers developing molecular strategies for reducing toxins in agricultural commodities like wheat.
Technical Abstract: Myrothecium roridum produces macrocyclic trichothecenes, the biosynthesis of which share a common beginning step with simple trichothecenes typically produced by Fusarium species, the cyclization of farnesyl pyrophosphate to form the sesquiterpene hydrocarbon trichodiene. A previous study showed that Myrothecium has a cluster of three 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 Myrothecium 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 three oxygenation steps and that the product of MrTRI4 is isotrichodiol.