Sex, MAT, and the Evolution of Fungal Virulence
While many fungi have a characterized sexual cycle, the pathogenic fungi represent a special example in which sexuality is uncommon and sexual mechanisms are unusual or cryptic. Given their evolutionary relationship to model organisms such as Saccharomyces cerevisiae, it is striking that many species of pathogenic fungi have never been observed to mate in the laboratory despite population genetic evidence for recombining population structures. The study of the role of sexual cycles of pathogenic fungi therefore takes center stage, promising to reveal much about how these pathogenic microbes evolve, enabling infection of humans and continued adaptation to unique challenges, such as the advent of new therapeutic interventions. This chapter provides a summary of our current knowledge of the role of mating in pathogenic fungi and discusses future directions in this field. It reviews recent studies that shed light on the role of sex and the evolution of virulence in Cryptococcus neoformans. MAT was subjected to ongoing intraand interallelic gene conversion, and inversions that suppress recombination that may be driven by the high transposon content of the locus. The infectious particle of the primary pathogen Cryptococcus immitis is also an asexually produced structure, the arthroconidium. Pneumocystis jiroveci is a common fungal pathogen of humans that is often acquired early in life. The mechanisms by which organisms recombine their genomes to produce recombinant offspring are central to our understanding of how organisms evolve and adapt to new environments.
