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Diversity of Species and Sexual Reproduction in the Fungal Genus Cryptococcus
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| 자료유형 | 학위논문 |
|---|---|
| 서명/저자사항 | Diversity of Species and Sexual Reproduction in the Fungal Genus Cryptococcus. |
| 개인저자 | Passer, Andrew Ryan. |
| 단체저자명 | Duke University. Molecular Genetics and Microbiology. |
| 발행사항 | [S.l.]: Duke University., 2019. |
| 발행사항 | Ann Arbor: ProQuest Dissertations & Theses, 2019. |
| 형태사항 | 148 p. |
| 기본자료 저록 | Dissertations Abstracts International 81-04B. Dissertation Abstract International |
| ISBN | 9781088333938 |
| 학위논문주기 | Thesis (Ph.D.)--Duke University, 2019. |
| 일반주기 |
Source: Dissertations Abstracts International, Volume: 81-04, Section: B.
Advisor: Heitman, Joseph. |
| 이용제한사항 | This item must not be sold to any third party vendors.This item must not be added to any third party search indexes. |
| 요약 | Speciation is a central mechanism of biological diversification. While speciation is well studied in plants and animals, in comparison, relatively little is known about speciation in fungi. One fungal model is the Cryptococcus genus, which is best known for the pathogenic Cryptococcus neoformans/Cryptococcus gattii species complex that causes >200,000 new human infections annually. Elucidation of how these species evolved into important human-pathogenic species remains challenging and can be advanced by studying the most closely related nonpathogenic species, Cryptococcus amylolentus and Tsuchiyaea wingfieldii. However, these species have only four known isolates, and available data were insufficient to determine species boundaries within this group. By analyzing full-length chromosome assemblies, we reappraised the phylogenetic relationships of the four available strains, confirmed the genetic separation of C. amylolentus and T. wingfieldii (now Cryptococcus wingfieldii), and revealed an additional cryptic species, for which the name Cryptococcus floricola is proposed. The genomes of the three species are ~ 6% divergent and exhibit significant chromosomal rearrangements, including inversions and a reciprocal translocation that involved intercentromeric ectopic recombination, which together likely impose significant barriers to genetic exchange. Using genetic crosses, we show that while C. wingfieldii cannot interbreed with any of the other strains, C. floricola can still undergo sexual reproduction with C. amylolentus. However, most of the resulting spores were inviable or sterile or showed reduced recombination during meiosis, indicating that intrinsic postzygotic barriers had been established.A second organism of interest from the Cryptococcus genus is C. depauperatus. This organism is unusual among the genus for its continuously activated sexual cycle. While other members of the genus enter their sexual cycle only under special circumstances, C. depauperatus is a homothallic (self-fertile) species that constantly produces basidiospores when grown on solid media. We sought to discover what genetic elements were responsible for its behavior. We began by analyzing its genome and found homologs of MF慣, a gene encoding an alpha pheromone, and STE3, a gene encoding a pheromone receptor. A phylogenetic analysis of the two genes shows that they are from opposite mating types and should be compatible with one another. To test whether MF慣 encodes a functional pheromone, we heterologously expressed it as a transgene in MATa and MAT慣 strains of C. neoformans. MATa cells with the transgene became self-filamentous, while MAT慣 cells were unaffected. We then made MATa MF慣 mutants that had a deletion of STE3 or STE6 (the pheromone exporter gene). All of the deletion mutants lost the propensity to self-filament. Therefore, MF慣 encodes a pheromone that can be detected by the Ste3 receptor of MATa cells and exported by Ste6. Additionally, we found that growth in liquid culture suppresses sporulation in C. depauperatus and used this fact to compare mRNA expression levels between cultures that were actively sporulating and those that were not. MF慣, STE3, and STE6 were all upregulated under conditions that permit sporulation. Thus, we have shown that one factor contributing to the constant sexual cycle of C. depauperatus is that it produces a pheromone and a pheromone receptor that are compatible with each other. |
| 일반주제명 | Microbiology. Genetics. |
| 언어 | 영어 |
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