Deletion of the sex-determining gene SXI1α enhances the spread of mitochondrial introns in Cryptococcus neoformans .

Background: Homing endonuclease genes (HEGs) are widely distributed genetic elements in the mitochondrial genomes of a diversity of eukaryotes. Due to their ability to self-propagate within and between genomes, these elements can spread rapidly in populations. Whether and how such elements are controlled in genomes remains largely unknown.

Results: Here we report that the HEG-containing introns in the mitochondrial COX1 gene in Cryptococcus neoformans are mobile and that their spread in sexual crosses is influenced by mating type ( MAT ) α-specific homeodomain gene SXI1 α. C. neoformans has two mating types, MAT a and MAT α . In typical crosses between strains of the two mating types , only a small portion (< 7%) of diploid fusants inherited the HEGs from the MAT α parent. However, disruption of the SXI1 α gene resulted in the majority (> 95%) of the diploid fusants inheriting the HEG-containing introns from the MAT α parent, a frequency significantly higher than those of intronless mitochondrial genes.

Conclusions: Our results suggest that SXI1 α not only determines uniparental mitochondrial inheritance but also inhibits the spread of HEG-containing introns in the mitochondrial genome in C. neoformans .