Asexuality in Fusarium oxysporum: Mechanisms and Relationship between Pathogenicity-Diversity

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Mating type (MAT) loci were cloned from asexual ascomycetes Fusarium oxysporum and Alternaria alternata by PCR-based strategy. Structure of the MAT loci in the genome of F. oxysporum was compared to that of Gibberella fujikuroi, a sexual relative of F. oxysporum. MAT1-1 idiomorph encodes three genes (Mat1-1-1, MAT1-1-2, and MAT1-1-3) which were highly homologous between the two species; MAT1-2 idiomorph encodes single MAT1-2-1 gene that was also homologous between the species. All of the MAT genes were confirmed to be expressed in asexual F. oxysporum when it was cultured on MM medium as well as in the sexual G. fujikuroi. A. alternata MAT genes (MAT1-1-1 and MAT1-2-1) were also expressed on MM medium and moreover both genes were proved to be functional by heterologous expression in Cochliobolus heterostrophus. These results suggested that the cause of asexuality in ascomycetes does not depend on MAT loci.