Isolation and characterisation of the mating-type (MAT) locus from Rhynchosporium secalis

The mating-type (MAT) genes from Rhynchosporium secalis were isolated using PCR-based methods. Characterisation of the MAT idiomorphs suggests that R. secalis is closely related to the discomycetes Pyrenopeziza brassicae and Tapesia yallundae in terms of sequence and MAT locus gene composition. The MAT1-2 idiomorph contains a single gene encoding a protein with a high-mobility group (HMG) DNA-binding domain. The MAT1-1 idiomorph contains two genes, one encoding a protein with a HMG domain and the other encoding an alpha box domain. A second, previously undescribed, intron was identified within the P. brassicae MAT1-2-1 gene. Two introns were also present in the corresponding gene in R. secalis and this showed the similarity between these genes at the discomycete MAT1-2 locus. Using PCR, we identified isolates of both mating types from barley crops in different parts of the UK and showed that the composition of the MAT idiomorphs is conserved in these isolates. These findings support the hypothesis that R. secalis is a heterothallic discomycete which has an as yet unidentified teleomorph.