Mitochondrial inheritance in haploid x non-haploid crosses in Cryptococcus neoformans

In the basidiomycetous yeast Cryptococcus neoformans, fusants and meiotic progeny from haploid-haploid (HH) crosses between strains of mating type a (MAT a) and mating type alpha (MATalpha) typically inherit mitochondrial DNA (mtDNA) from the MAT a parent. In this study, we investigated the mtDNA inheritance pattern in haploid x non-haploid crosses. A total of 420 meiotic progeny and 173 fusants were obtained from five crosses and analyzed for two polymorphic mitochondrial markers. The percentage of meiotic progeny and fusants inheriting mtDNA from MATalpha or MATalpha/alpha parents ranged from 8 to 50%. The leakage was significantly greater than those observed in HH crosses, indicating that mtDNA inheritance is not uniparental in haploid x non-haploid crosses in C. neoformans. In addition, mtDNA leakage in the fusants, but not the meiotic progeny, of the MATalpha/alpha x MAT a cross was significantly higher than that in the MAT a/a x MATalpha cross, suggesting that the diploid parents with different mating types contribute differently in determining fusant mtDNA genotype in these crosses. Flow cytometry analysis revealed that meiotic progeny population of each cross was of mixed ploidy while the ploidy level of the selected fusants ranged from diploid to triploid.