Email updates

Keep up to date with the latest news and content from BMC Evolutionary Biology and BioMed Central.

Open Access Research article

The evolutionary trajectory of the mating-type (mat) genes in Neurospora relates to reproductive behavior of taxa

Lotta Wik1, Magnus Karlsson2 and Hanna Johannesson3*

Author Affiliations

1 Swedish University of Agricultural Sciences, Department of Biomedical Sciences and Veterinary Public Health, Husargatan 3, SE-75123 Uppsala, Sweden

2 Swedish University of Agricultural Sciences, Department of Forest Mycology and Pathology, Ulls väg 26, SE-750 07 Uppsala, Sweden

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

For all author emails, please log on.

BMC Evolutionary Biology 2008, 8:109  doi:10.1186/1471-2148-8-109

Published: 11 April 2008

Abstract

Background

Comparative sequencing studies among a wide range of taxonomic groups, including fungi, have led to the discovery that reproductive genes evolve more rapidly than other genes. However, for fungal reproductive genes the question has remained whether the rapid evolution is a result of stochastic or deterministic processes. The mating-type (mat) genes constitute the master regulators of sexual reproduction in filamentous ascomycetes and here we present a study of the molecular evolution of the four mat-genes (mat a-1, mat A-1, mat A-2 and mat A-3) of 20 Neurospora taxa.

Results

We estimated nonsynonymous and synonymous substitution rates of genes to infer their evolutionary rate, and confirmed that the mat-genes evolve rapidly. Furthermore, the evolutionary trajectories are related to the reproductive modes of the taxa; likelihood methods revealed that positive selection acting on specific codons drives the diversity in heterothallic taxa, while among homothallic taxa the rapid evolution is due to a lack of selective constraint. The latter finding is supported by presence of stop codons and frame shift mutations disrupting the open reading frames of mat a-1, mat A-2 and mat A-3 in homothallic taxa. Lower selective constraints of mat-genes was found among homothallic than heterothallic taxa, and comparisons with non-reproductive genes argue that this disparity is not a nonspecific, genome-wide phenomenon.

Conclusion

Our data show that the mat-genes evolve rapidly in Neurospora. The rapid divergence is due to either adaptive evolution or lack of selective constraints, depending on the reproductive mode of the taxa. This is the first instance of positive selection acting on reproductive genes in the fungal kingdom, and illustrates how the evolutionary trajectory of reproductive genes can change after a switch in reproductive behaviour of an organism.