Identification of a Diploid Self-sporulating Cycle in the Basidiomycetous Yeast Rhodosporidium toruloides

Self-sporulating diploid and aneuploid cells were identified in the life cycle of Rhodosporidium toruloides by microscopic observation of nuclear behaviour, microphotometry of DNA content, and genetic characterization of progeny. From a sexual cross between haploid A- and a-type strains, diploid progeny with both A and a mating-type loci and aneuploid progeny with either A or a mating-type locus were isolated in addition to haploid progeny. The diploid isolates propagated by budding in yeast form and eventually developed monokaryotic hyphae. The diploid hyphae formed uninucleate teliospores and blastospores from which diploid yeast cells were isolated (self-sporulating). Aneuploids carrying the A or a mating-type isolated from a sexual cross and from self-sporulating diploids entered the sexual cycle like haploid cells. The life cycle consisting of sexual and self-sporulating cycles is presented.