Canadian Forest Service Publications

Unequal recombination and evolution of the mating-type (MAT) loci in the pathogenic fungus Grosmannia clavigera and relatives. 2013. Tsui, C.K.-M.; DiGuistini, S.; Wang, Y.; Feau, N.; Dhillon, B.; Bohlmann, J.; Hamelin, R.C. Genes, Genomes, Genetics 3: 465-480.

Year: 2013

Available from: Laurentian Forestry Centre

Catalog ID: 34764

Language: English

CFS Availability: PDF (request by e-mail)

Abstract

Sexual reproduction in fungi is regulated by the mating-type (MAT) locus where recombination is suppressed. We investigated the evolution of MAT loci in eight fungal species belonging to Grosmannia and Ophiostoma (Sordariomycetes, Ascomycota) that include conifer pathogens and beetle symbionts. The MAT1-2 idiomorph/allele was identified from the assembled and annotated Grosmannia clavigera genome, and the MAT locus is flanked by genes coding for cytoskeleton protein (SLA) and DNA lyase. The synteny of these genes is conserved and consistent with other members in Ascomycota. Using sequences from SLA and flanking regions, we characterized the MAT1-1 idiomorph from other isolates of G. clavigera and performed dotplot analysis between the two idiomorphs. Unexpectedly, the MAT1-2 idiomorph contains a truncated MAT1-1-1 gene upstream of the MAT1-2-1 gene that bears the high-mobility-group domain. The nucleotide and amino acid sequence of the truncated MAT1-1-1 gene is similar to its homologous copy in the MAT1-1 idiomorph in the opposite mating-type isolate, except that positive selection is acting on the truncated gene and the alpha(a)-box that encodes the transcription factor has been deleted. The MAT idiomorphs sharing identical gene organization were present in seven additional species in the Ophiostomatales, suggesting that the presence of truncated MAT1-1-1 gene is a general pattern in this order. We propose that an ancient unequal recombination event resulted in the ancestral MAT1-1-1 gene integrated into the MAT1-2 idiomorph and surviving as the truncated MAT1-1-1 genes. The a-box domain of MAT1-1-1 gene, located at the same MAT locus adjacent to the MAT1-2-1 gene, could have been removed by deletion after recombination due to mating signal interference. Our data confirmed a 1:1 MAT/sex ratio in two pathogen populations, and showed that all members of the phiostomatales studied here including those that were previously deemed asexual have the potential to reproduce sexually. This ability can potentially increase genetic variability and can enhance fitness in new, ecological niches.

Plain Language Summary

Researchers studied the reproduction of fungal species belonging to the genera Ophiostoma and Grosmannia. Grosmannia species are associated with forest diseases such as black-stain root disease, which attacks many conifers in British Columbia including lodgepole pine, white spruce and Western hemlock. Grosmannia fungi are also responsible for blue-stain disease, which decreases the market value of forest products. Species of the genus Ophiostoma are at the root of several forest diseases, including Dutch elm disease, which destroyed some 600,000 elms in Quebec between 1945 and 1960.

These fungal species were recognized as having asexual reproduction. However, the results of this research demonstrate that they have the potential to reproduce sexually. This ability could increase the genetic variability of these fungi, thus allowing them to adapt to new environmental conditions.

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