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Open Access Research article

Analyses of expressed sequence tags in Neurospora reveal rapid evolution of genes associated with the early stages of sexual reproduction in fungi

Kristiina Nygren15, Andreas Wallberg2, Nicklas Samils1, Jason E Stajich3, Jeffrey P Townsend4, Magnus Karlsson1 and Hanna Johannesson5*

Author Affiliations

1 Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Box 7026, SE-75007, Uppsala, Sweden

2 Department of Medical Biochemistry and Microbiology, Uppsala University, Box 582, SE-751, Uppsala, Sweden

3 Department of Plant Pathology and Microbiology, University of California at Riverside, 900 University Avenue, Riverside, CA, 92521, USA

4 Department of Ecology and Evolutionary Biology, Yale University, 165 Prospect St., New Haven, CT, 06520-8106, USA

5 Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18 D, SE-752 36, Uppsala, Sweden

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BMC Evolutionary Biology 2012, 12:229  doi:10.1186/1471-2148-12-229

Published: 27 November 2012

Abstract

Background

The broadly accepted pattern of rapid evolution of reproductive genes is primarily based on studies of animal systems, although several examples of rapidly evolving genes involved in reproduction are found in diverse additional taxa. In fungi, genes involved in mate recognition have been found to evolve rapidly. However, the examples are too few to draw conclusions on a genome scale.

Results

In this study, we performed microarray hybridizations between RNA from sexual and vegetative tissues of two strains of the heterothallic (self-sterile) filamentous ascomycete Neurospora intermedia, to identify a set of sex-associated genes in this species. We aligned Expressed Sequence Tags (ESTs) from sexual and vegetative tissue of N. intermedia to orthologs from three closely related species: N. crassa, N. discreta and N. tetrasperma. The resulting four-species alignments provided a dataset for molecular evolutionary analyses. Our results confirm a general pattern of rapid evolution of fungal sex-associated genes, compared to control genes with constitutive expression or a high relative expression during vegetative growth. Among the rapidly evolving sex-associated genes, we identified candidates that could be of importance for mating or fruiting-body development. Analyses of five of these candidate genes from additional species of heterothallic Neurospora revealed that three of them evolve under positive selection.

Conclusions

Taken together, our study represents a novel finding of a genome-wide pattern of rapid evolution of sex-associated genes in the fungal kingdom, and provides a list of candidate genes important for reproductive isolation in Neurospora.

Keywords:
Neurospora; Reproductive genes; dN/dS; Speciation; Microarray