Artificial Mating-Type Conversion and Repetitive Mating for Polyploid Generation

The yeast Saccharomyces cerevisiae is one of the best-understood biological systems and can produce numerous useful compounds. Sexual hybridization (mating) can drive dramatic evolution of yeasts by the inheritance of half of the parental genomic information from each cell. Unfortunately, half of the parental genomic information is lost in individual cells in the next generation. Additionally, recombination of homologous chromosomes during meiosis gives rise to diversity in the next generation; hence, it is commonly employed to identify targets from diverse cell populations, based on the mating machinery. Here, we established a system for generating polyploids that inherit all genetic information from the parental strains via artificial mating-type conversion and repetitive mating. We prepared α-type haploid strains whose chromosomes were tagged with genes encoding fluorescent proteins or transcriptional factors. Only the mating-type locus was successfully converted from α-type to a-type sequence by the endonuclease Ho, and the resultant a-type cells mated with each α-type haploid to yield an a/α-type diploid strain with all genetic information from both parental strains. Importantly, we repeatedly converted the mating-type of polyploid cells to obtain a-type cells capable of mating with α-type cells. This approach can potentially facilitate yeast-strain development with unparalleled versatility, utilizing vast available resources.