Characterization of Sex and Meiosis in the Fungal Pathogen Candida lusitaniae

Sexual reproduction of eukaryotic species provides an adaptive advantage over organisms that replicate asexually. Many genes essential for sex have been identified in the model yeast S. cerevisiae, and are conserved in the human pathogen Candida lusitaniae.  Interestingly, C. lusitaniae is able to complete a meiotic program even though it has lost IME1, the master regulator of S. cerevisiae meiosis.  This observation suggests that C. lusitaniae has evolved an alternative transcriptional regulation of meiosis.  In this study, we used genetic and genomic approaches to explore the regulation of the complete sexual life cycle of C. lusitaniae.  Our gene profiling showed that many homologs of S. cerevisiae mating and meiosis genes have a similar temporal order of gene expression during the C. lusitaniae sexual cycle. Surprisingly, however, we observed induction of the pheromone response pathway during meiosis and, conversely, expression of meiosis genes during mating.  We further show that cells actively secrete pheromone during meiosis and that the key meiotic regulator, IME2, is necessary for both mating and meiosis in C. lusitaniae.  The simultaneous expression of both mating and meiosis genes is reminiscent of a fused sexual program similar to that in the distantly related yeast, Schizoasaccharomyces pombe. Our study therefore establishes a novel model of sexual regulation in C. lusitaniae that shows both similarities and differences with the mating cycles of S. cerevisiae and S. pombe, and begins to shed light on the evolution of the sexual program in ascomycete yeast.