The cell type ofRhodosporidium toruloides after protoplast fusion between strains of identical and opposite mating type

Protoplast fusions between strains of identical and of opposite mating type were performed. Sexual crosses and protoplast fusions inRhodosporidium toruloides led to different hybrid types. Sexual crosses gave rise exclusively to a dikaryotic mycelium. In protoplast fusions between strains of identical mating type (A ora), monokaryotic yeast-like hybrids which sustained the parental mating type were obtained. In protoplast fusions between strains of opposite mating type, the majority of the hybrids belonged to theMyc ⁺ type, i.e., the hybrids grew like yeasts, able to switch over spontaneously to mycelial growth. In addition to theMyc ⁺ types, up to 10% real yeast hybrids and less than 5% dikaryotic mycelia were obtained. Obviously the cell type inR. toruloides is under the control of the mating type alleles.