Two ascomycete classes based on fruiting-body characters and ribosomal DNA sequence

Area of Science:

• Mycology
• Molecular Systematics
• Fungal Phylogenetics

Background:

• Traditional ascomycete classification relies on fruiting body morphology, which is increasingly recognized as unreliable due to convergent evolution.
• The lack of stable unifying characters hinders the classification of major ascomycete groups and supraordinal relationships.

Purpose of the Study:

• To investigate the phylogenetic relationships within Ascomycota using molecular data.
• To determine if molecular data can provide stable characters for unifying ascomycete groups and enabling supraordinal classification.

Main Methods:

• Sequencing of both strands of 18S ribosomal DNA (rDNA) from nine ascomycete fungi.
• Phylogenetic analysis incorporating three additional sequences from GenBank.
• Inference of phylogeny using 162 informative sites from 1,700 bp of DNA sequence data, with yeast as an outgroup.

Main Results:

• Phylogenetic analysis divided the studied fungi into two distinct groups.
• These molecularly defined groups showed strong correlation with traditional classifications based on fruiting body types (cleistothecia and perithecia).
• Genera like Talaromyces, Ajellomyces capsulatus, Eremascus albus, and Ascosphaera apis were placed within the plectomycete group, while the Dutch elm disease fungus grouped with pyrenomycetes.

Conclusions:

• Molecular data, specifically 18S rDNA sequences, provide robust characters for ascomycete classification.
• The findings support the division of ascomycetes into two major clades, largely corresponding to the traditional classes Plectomycetes and Pyrenomycetes.
• This molecular approach offers a more stable foundation for resolving ascomycete phylogeny and supraordinal classification.