EVIDENCE FOR A GENE-CLUSTER INVOLVING TRICHOTHECENE-PATHWAY BIOSYNTHETIC GENES IN FUSARIUM-SPOROTRICHIOIDES

Two overlapping cosmid clones (Cos1-1 and Cos9-1) carrying the Tox5 ge ne were isolated from a library of F. sporotrichioides strain NRRL 329 9 genomic DNA. These cosmids were used to transform three T-2 toxin-de ficient mutants that are blocked at different steps in the trichothece ne pathway. Both cosmids restored T-2 toxin production to Tox3-1- or T ox4-1- mutants but neither restored T-2 toxin production to a Tox1-2- mutant. The production of T-2 toxin by the complemented Tox3-1- and To x4-1- mutants, as well as the production of diacetoxyscirpenol by the cosmid-transformed Tox1-2- mutant, were 2- to 10- fold higher than in strain NRRL 3299. In addition, those transformants carrying Cos9-1 pro duced significantly higher levels of trichothecenes than transformants carrying Cos1-1. Two different DNA fragments (FSC13-9 and FSC14-5), r epresenting the region of overlap between the cosmid clones, were isol ated. These fragments specifically complemented either the Tox3-1- mut ant (FSC14-5) or the Tox4-1- mutant (FSC13-9). The trichothecene-produ ction phenotype of these transformants was similar to NRRL 3299. These results suggest that two or more genes involved in the biosynthesis o f trichothecenes are closely linked to Tox5.