Sexual Reproduction of Cryptococcus
This chapter reviews the discovery of both opposite-sex and unisexual reproduction and illustrates how these pathways are molecularly controlled and the central cell biology questions that remain to be addressed. Fungal sexual reproduction is genetically regulated by the mating-type locus (MAT), a specialized region of the genome that is idiomorphic or allelic between different sexes. Similar to the model fission yeast Schizosaccharomyces pombe, mating and meiosis of Cryptococcus neoformans occur sequentially in response to limitation or specific nutrient cues. Other environmental cues such as light and temperature also affect mating of C. neoformans. Those factors that have been connected to the sexual reproduction of C. neoformans are summarized in the chapter. Furthermore, several Cryptococcus species can be isolated from trees and fermenting fruits, suggesting that there might be potential plant-fungus interactions that contribute to sexual reproduction of C. neoformans and Cryptococcus gattii in nature. Apart from nutritional cues, other environmental signals also influence sexual reproduction. However, the predominance of the α mating type (>99%) in the Cryptococcus population represents a paradox as to how sexual reproduction might occur in this essentially unisexual population. The discovery of same-sex mating in C. neoformans resulted in a paradigm shift in considering how genetic diversity is generated in a unisexual population and the evolutionary role of a unisexual reproductive mode. Moreover, the transitions that occur in the fungal kingdom between heterothallic outbreeding and homothallic inbreeding modes promise to reveal general features by which sexual reproduction enhances fitness and enables evolutionary success throughout biology.
