Development of growth selection systems to isolate a-type or α-type of yeast cells spontaneously emerging from MATa/α diploids

Background: Manufacture of MATa and MAT alpha yeast cells is required for crossbreeding, a procedure that permits hybridization and the generation of new heterozygous strains. Crossbreeding also can be performed with a- and alpha- type of cells, which have the same mating abilities as MATa and MAT alpha haploid cells, respectively. Results: In this work, we describe a method to generate a- and alpha- type of cells via the naturally-occurring chromosomal aberration in parental MATa/alpha diploids. We successfully designed suitable genetic circuits for expression of the URA3 selection marker gene to permit isolation of a- and alpha- type of cells, respectively, on solid medium lacking uracil. Furthermore we succeeded in generation of zygotes by mating of both the manufactured a- and alpha- type of yeast cells. Conclusions: This process does not require exposure to mutagens such as UV irradiation, thereby avoiding the accumulation of undesirable mutations that would detract from the valuable traits that are under study. All the genetic modifications in the current study were introduced into yeast cells using plasmids, meaning that these traits can be removed without altering the genome sequence. This approach provides a reliable and versatile tool for scientific research and industrial yeast crossbreeding.