Cloning of the mating type loci from Pyrenopeziza brassicae reveals the presence of a novel mating type gene within a discomycete MAT 1-2 locus encoding a putative metallothionein-like protein.

The mating type loci were cloned from Pyrenopeziza brassicae by chromosome walking from a mating type-linked polymerase chain reaction (PCR) fragment and shown to be idiomorphic by sequence analysis. The MAT 1-1 locus is approximately 3.2 kb and contains a single gene encoding a putative high-mobility group (HMG) domain protein. The MAT 1-2 locus is approximately 3.9 kb with three open reading frames (ORFs) encoding a putative HMG domain, an alpha-1 domain and metallothionein-like proteins. The putative alpha-1 domain ORF on MAT 1-2 is transcribed in the opposite orientation to the other two transcripts and extends into non-idiomorphic sequence. This is the first report of sequence analysis of the mating type loci from a discomycete fungus, which has revealed an interesting mating type infrastructure within the MAT 1-2 locus. Although metallothionein-like proteins have been implicated in a number of processes in animals and plants, they have not to date been implicated in the mating process of filamentous fungi. Possible roles for metallothionein-like proteins in the mating process are discussed.