Gene duplication and loss are important mechanistic antecedents in generating functional diversification. Here we adopted a phylogenomic approach with fungi of very different virulence and habitat to survey and characterize their serine proteinases (subtilases and trypsins) with the goal of providing a framework of information on these important enzymes, as well as improving understanding of general processes in fungal gene family evolution. The survey was based on 9 fungal genomes and expressed sequence tags from the insect pathogen Metarhizium anisopliae. Comparing subtilases between species revealed that basidiomycetes (Cryptococcus neoformans, Coprinus cinereus, Ustilago maydis) and saprophytic ascomycetes (Saccharomyces cerevisiae, Schizosaccharomyces pombe, Aspergillus nidulans, Neurospora crassa) lack the large gene families encoding secreted enzymes found in the pathogenic ascomycetes (M. anisopliae, M agnaporthe grisea, Fusarium graminearum). Patterns of intron loss and the degree of divergence between paralogs indicate that the proliferation of subtilisins classes I and II in pathogens occurred after the basidiomycete/ascomycete split but predated radiation of ascomycete lineages. This suggests that the early ascomycetes had a lifestyle that selected for multiple proteases, while the current disparity in gene numbers between ascomycete lineages results from retention of genes in pathogens that have been lost in saprophytes. However, the pathogens retained and occasionally expanded different gene families. Thus, M. grisea has 15 class I subtilisins and 6 class II subtilisins, while M. anisopliae and F. graminearum each possess 11 class II subtilisins but three or fewer class I subtilisins. This reveals evolutionary selection of different gene families among Ascomycete fungi. A prevailing trend towards lineage specific gene loss was shown by the distribution of trypsins across 35 representative fungi. Trypsin genes are lacking in most saprophytes, but are present in a basidiomycete insect symbiont (Septobasidium canescens), most zygomycetes and many ascomycete plant and insect pathogens. The patchy distribution of trypsins suggest that their phylogenetic breadth will have been much wider in early fungi than currently and confirms the dynamic nature of the fungal genome.
Full conference title:
23rd Fungal Genetics Conference
- Fungal Genetics Conference 23rd (2002)