Novel mating-type-associated genes and gene fragments in the genomes of Mycosphaerellaceae and Teratosphaeriaceae fungi

The mating-type (MAT1) locus encodes transcription factors essential for the onset of the sexual cycle in ascomycete fungi. This locus has been characterised in only a few heterothallic, plant pathogenic Mycosphaerellaceae and Teratosphaeriaceae. We used available genome sequences for Mycosphaerellales species to investigate the presence of two unique mating-type-associated features. The accessory MAT1 genes, MAT1-1-10 (MATORF2) and MAT1-2-12 (MATORF1), typically occurred in both MAT idiomorphs of Mycosphaerellaceae species. In contrast, they were associated with only one idiomorph in Teratosphaeriaceae species. In Pseudocercospora, phylogenetic analyses showed that homologs present in different idiomorphs were paralogous and subject to different selective pressures, indicating that their evolution is linked to mating type. In almost half of the investigated Mycosphaerellales genomes, numerous short fragment sequences, almost identical to portions of the MAT1-1-1 and MAT1-2-1 genes, were present in multiple areas outside of the MAT1 locus. Aligned to the MAT1 genes, these sequences resembled an mRNA transcript. Fragment sequences were similar among species groups and occurred at the same genomic positions, implying that monophyletic groups have the same origins of these sequences. Although the functions of the MAT fragment sequences and accessory MAT1 genes remain unknown, both were expressed in the representative Mycosphaerellaceae and Teratosphaeriaceae species that were investigated.