The mating type-specific homeodomain genes SXI1α and SXI2a coordinately control uniparental mitochondrial inheritance in Cryptococcus neoformans

In the great majority of sexual eukaryotes, mitochondrial genomes are inherited almost exclusively from a single parent. While many hypotheses have been proposed to explain this phenomenon, very little is known about the genetic elements controlling uniparental mitochondria inheritance. In the bipolar, isogamous basidiomycete yeast Cryptococcus neoformans, progeny from crosses between strains of mating type a (MATa) and mating type alpha (MAT alpha) typically inherit mitochondrial DNA (mtDNA) from the MATa parent. We recently demonstrated that a mating type alpha (MAT alpha)-specific gene SXI1 alpha, controls mitochondrial inheritance in C. neoformans. Here, we show that another homeodomain gene SXI2a in the alternative mating type MATa is also required for uniparental mtDNA inheritance in this fungus. Disruption of SXI2a resulted in biparental mtDNA inheritance in the zygote population with significant numbers of progeny inheriting mtDNA from the MATa parent, the MAT alpha parent, and both the MATa and the MAT alpha parents. In addition, progeny from same-sex mating between MAT alpha strains showed a biparental mitochondrial inheritance pattern. Our results suggest that SXI1 alpha and SXI2a coordinately control uniparental mitochondrial inheritance in C. neoformans.