Concordant evolution of trichothecene 3-O-acetyltransferase and an rDNA species phylogeny of trichothecene-producing and non-producing fusaria and other ascomycetous fungi

The cereal pathogen Fusarium graminearum species complex (e.g. Fusarium asiaticum, previously referred to as F graminearum lineage 6) produces the mycotoxin trichothecene in infected grains. The fungus has a gene for self-defence, Tri101, which is responsible for 3-O-acetylation of the trichothecene skeleton in the biosynthetic pathway. Recently, trichothecene non-producers Fusarium oxysporum and Fusarium fujikuroi (teleomorph Gibberella fujikuroi) were shown to have both functional (Tri201) and non-functional (pseudo-Tri101) trichothecene 3-O-acetyltransferase genes in their genome. To gain insight into the evolution of the trichothecene genes in Gibberella species, the authors examined whether or not other (pseudo-)biosynthesis-related genes are found near Tri201. However, sequence analysis of a 12 kb region containing Tri201 did not result in identification of additional trichothecene (pseudo-)genes in F oxysporum. In a further attempt to find other trichothecene (pseudo-)genes from the non-producer, the authors examined whether or not the non-trichothecene genes flanking the ends of the core trichothecene gene cluster (i.e. the Tri5 cluster) comprise a region of synteny in Gibberella species. However, it was not possible to isolate trichothecene (pseudo-)genes from F oxysporum (in addition to the previously identified pseudo-Tri101), because synteny was not observed for this region in F asiaticum and F oxysporum. In contrast to this unsuccessful identification of additional trichothecene (pseudo-)genes in the non-producer, a functional trichothecene 3-O-acetyltransferase gene could be identified in fusaria other than Gibberella: Fusarium decemcellulare and Fusarium solani; and in an ascomycete from a different fungal genus, Magnaporthe grisea. Together with the recent functional identification of Saccharomyces cerevisiae ScAYT1, these results are suggestive of a different evolutionary origin for the trichothecene 3-O-acetyltransferase gene from other biosynthesis pathway genes. The phylogeny of the 3-O-acetyltransferase was mostly concordant with the rDNA species phylogeny of these ascomycetous fungi.