Abstract
The heterothallic basidiomycetous fungus Cryptococcus neoformans has two mating types, MATa and MATα. Morphological progression of bisexual reproduction in C. neoformans is as follows: yeast to hyphal transition, filament extension, basidium formation, meiosis, and sporulation. C. neoformans Cdk-related kinase 1 (CRK1) is a negative regulator of bisexual mating. In this study, we characterized the morphological features of mating structures in the crk1 mutant and determined the genetic interaction of CRK1 in the regulatory networks of sexual differentiation. In the bilateral crk1 mutant cross, despite shorter length of filaments than in the wild-type cross, dikaryotic filaments and other structures still remained intact during bisexual mating, but the timing of basidium formation was approximately 18 h earlier than in the cross between wild type strains. Furthermore, gene expression analyses revealed that CRK1 modulated the expression of genes involved in the progression of hyphal elongation, basidium formation, karyogamy and meiosis. Phenotypic results showed that, although deletion of C. neoformans CRK1 gene increased the efficiency of bisexual mating, filamentation in the crk1 mutant was blocked by MAT2 or ZNF2 mutation. A bioinformatics survey predicted the C. neoformans GATA transcriptional factor Gat1 as a potential substrate of Crk1 kinase. Our genetic and phenotypic findings revealed that C. neoformans GAT1 and CRK1 formed a regulatory circuit to negatively regulate MAT2 to control filamentation progression and transition during bisexual mating.
Highlights
Cryptococcus spp. are a group of basidiomycetous fungi that can be isolated from pigeon droppings, soil and trees and cause meningitis in humans [1,2]
Our results demonstrated that deletion of GAT1 can only partially restore the repression of dikaryotic filamentation and gene expression conferred by Cdk-related kinase 1 (CRK1) overexpression, suggesting that Gat1 may not be the only downstream target of Crk1 to regulate bisexual mating
Previous studies indicated that C. neoformans CRK1 plays a negative role in cell fusion and pheromone expression in bisexual mating [29]
Summary
Cryptococcus spp. are a group of basidiomycetous fungi that can be isolated from pigeon droppings, soil and trees and cause meningitis in humans [1,2]. Infection with two major Cryptococcus species, C. neoformans and C. gattii, results in cryptococcosis [3]. C. gattii is distributed in tropical or subtropical areas and infects immunocompetent individuals [4,5,6], whereas C. neoformans is the major human fungal pathogen that infects AIDS patients worldwide. C. neoformans grows vegetatively as yeast cells and is a bipolar heterothallic fungus that has mating type MATa and MATα cells. The life cycle of C. neoformans has been described [7]. Several environmental conditions, such as nitrogen starvation, room temperature, and the presence of mating pheromone, trigger bisexual differentiation and same-sex mating in C. neoformans. Sexual development in C. neoformans starts with a morphological transition from a yeast form to a filamentous hypha
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