Diversity of Mating-Type Chromosome Structures in the Yeast Zygosaccharomyces rouxii Caused by Ectopic Exchanges between MAT-Like Loci

We investigated sex chromosome diversity in Zygosaccharomyces rouxii (Z. rouxii). In the current study, we show that the organization of the mating-type (MAT) locus is highly variable in the Z. rouxii population, indicating the MAT, HML, and HMR loci are translocation hotspots. Although NBRC1130 and CBS732 were originally two stocks of the type strain of the species, only NBRC1130 retains the original karyotype. A reciprocal translocation between the MAT and HMR loci appears to have occurred during the early passage culture of CBS732, which was used for genome sequencing. In NBRC1733, NBRC0686, NBRC0740 and NBRC1053, the terminal region of the chromosome containing the HMR locus was replaced with the chromosomal region to the left of the MAT or HML loci. The translocation events found in NBRC1733, NBRC0686, NBRC0740, and NBRC1053 were reconstructed under our experimental conditions using the DA2 background, and the reconstruction suggests that the frequency of this type of translocation is approximately 10(−7). These results suggest that the MAT and MAT-like loci were the susceptible regions in the genome, and the diversity of mating-type chromosome structures in Z. rouxii was caused by ectopic exchanges between MAT-like loci.