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Conflict between reproductive gene trees and species phylogeny among heterothallic and pseudohomothallic members of the filamentous ascomycete genus Neurospora
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Evolutionary Biology.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Evolutionary Biology.
Department of Forest Mycology and Pathology, Swedish University of Agricultural Sciences.
Department of Ecology and Evolutionary Biology, University of Michigan.
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2010 (English)In: Fungal Genetics and Biology, ISSN 1087-1845, E-ISSN 1096-0937, Vol. 47, no 10, 869-878 p.Article in journal (Refereed) Published
Abstract [en]

In this study, we investigated the genealogies of genes important for sexual identity, i.e. mating-type (mat) and pheromone-receptor (pre) genes, among heterothallic and peudohomothallic taxa of Neurospora. The resulting genealogies were compared with the species phylogeny derived from non-coding sequences. We found conflicting topologies between the reproductive genealogies and the species phylogeny, and these conflicts were supported by both node support analyses and likelihood tests on the relative fit of datasets to alternative phylogenetic hypotheses. We argue that reproductive genes are more permeable to gene flow, i.e. are more often introgressed between species of Neurospora, than other parts of the genome. Certain conflicts between the species phylogeny and both mat genealogies were observed, suggesting that the two mating-type idiomorphs were selectively introgressed into a species from a single ancestral source. Taken together, the results presented here highlight complex evolutionary trajectories of reproductive genes in the fungal kingdom, which may be of importance for reproductive behavior in natural populations.

Place, publisher, year, edition, pages
2010. Vol. 47, no 10, 869-878 p.
Keyword [en]
Ascomycota, Evolution, Heterothallism, Mating type, Pheromone receptor, Pseudohomothallism
National Category
Biological Sciences
URN: urn:nbn:se:uu:diva-167867DOI: 10.1016/j.fgb.2010.06.008ISI: 000281999900009PubMedID: 20601044OAI: oai:DiVA.org:uu-167867DiVA: diva2:488658
Available from: 2012-02-02 Created: 2012-02-02 Last updated: 2016-04-26Bibliographically approved
In thesis
1. On the Evolution of Reproductive Systems in Neurospora
Open this publication in new window or tab >>On the Evolution of Reproductive Systems in Neurospora
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis was to study the evolution of reproductive systems and reproductive traits in the fungal genus Neurospora. More specifically, I have investigated the evolutionary forces shaping the genes involved in sexual reproduction, focusing on mating-type (mat) and pheromone receptor (pre) genes. Neurospora contains species exhibiting three different mating systems, i.e., heterothallism (self-incompatibility), homothallism (self-compatibility) and pseudohomothallism (partial self-incompatibility). First, a robust phylogeny of Neurospora was established. The phylogenetic analyses revealed multiple independent transitions in reproductive life style during the evolutionary history of the genus. We argued for a heterothallic ancestor of the genus, although our subsequent ancestral reconstruction analyses favored a homothallic ancestor. To be able to settle the ancestral mating system, we zoomed in on the structural architecture of the mat-locus in four homothallic species of Neurospora, thought to have arisen from independent transitions. Our results led us to suggest two different genetic mechanisms (translocation and unequal crossover) to explain the transitions in mating system from heterothallism to homothallism. We pointed out that the mating-system transitions in Neurospora are unidirectional, and suggested that transposable elements might be driving the transitions. In conclusion, we suggest a heterothallic ancestor for Neurospora, and that at least six transitions to homothallism and two transitions to pseudohomothallism have occurred in its evolutionary history. Further, we used the phylogeny of Neurospora as a framework to test if the evolution of pre-genes (pre-1 and pre-2) in hetero- and homothallic Neurospora is dependent on mating systems and/or even the homothallic clades themselves (i.e., mating-system and/or switch-dependent). The molecular evolution results suggest that pre-1 and pre-2 are overall functional in both homothallic and heterothallic Neurospora. The molecular evolution of pre-1 seems to be independent of mating-system or homothallic clade, and we detected signs for positive selection in the C-terminal tail. For pre-2 we found no support for mating-system dependent evolution, but indications for switch-dependent evolution. In this study we also included expression analyses of both pre- as well as mat-genes, with the prospect to assess functionality and regulation. During this thesis work, we also performed a phylogenetic study were we found that reproductive genes might be more permeable to introgression than other genes, which is in contrast to theoretical expectations. In the last study, we confirmed the co-existence of two alternative splice variants of the pheromone receptor gene pre-1 in Neurospora crassa, and performed expression profiles studies using quantitative RT-PCR. I hope this thesis work will further strengthen Neurospora as a model for research in evolutionary genetics.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 41 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 895
Neurospora, mating type, pheromone receptor, phylogeny, gene expression, heterothallism, homothallism, pseudohomothallism, alternative splicing
National Category
Natural Sciences
Research subject
Biology with specialization in Evolutionary Genetics
urn:nbn:se:uu:diva-167875 (URN)978-91-554-8265-7 (ISBN)
Public defence
2012-03-16, Lindahlsalen, EBC, Norbyvägen 14, Uppsala, 09:15 (English)
Available from: 2012-02-24 Created: 2012-02-02 Last updated: 2012-03-01Bibliographically approved

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