New Branch in Fungal Evolution Discovered

A new study by University of Alberta scientists has helped to classify ~600 fungi that, previously, lacked a place among the fungi family tree. The study, led by Dr. Toby Spribille, assistant professor at Alberta, is published in Current Biology.

“Ascomycota account for about two-thirds of named fungal species. Over 98% of known Ascomycota belong to the Pezizomycotina, including many economically important species as well as diverse pathogens, decomposers, and mutualistic symbionts,” write Spribille and colleagues.

Ascomycota is a phylum of the Fungi kingdom. There are three subphyla of Ascomycota: Pezizomycotina, Saccharomycotina and Taphrinomycotina.

Our current knowledge on Pezizomycotina evolution has been based on sampling well-defined taxonomic classes. But Spribille and colleagues argue that “considerable diversity exists in undersampled and uncultured, putatively early-diverging lineages”, and the effects of these on evolutionary models has been understudied. These early-diverging lineages are the focus of Spribille and team’s latest study, where they obtained the genomes of 30 lineages and used DNA-based dating techniques to explore their evolution.

The researchers liken these fungi to Australian creatures called monotremes, which produce milk and have nipples, but lay eggs. They have defied classification systems, and at one point, debate stirred as to whether they were even real. “Though nobody thought our fungi were fake, it’s similar because they all look totally different,” says Spribille.

Finding a classification home for fungi

The researchers found that all classes but one descended from a single origin over 300 million years ago. The data suggests they were once “sprinkled” across seven different classes, a “high-level grouping” that would be similar to how we sub-group animals.

“They were classified, but they were classified into such different parts of the fungal side of the tree of life that people never suspected they were related to each other,” says Dr. David Díaz-Escandón, who conducted the research as part of his PhD thesis.

The level of variation among the fungi was high – including “eerie” tongue-shaped fungi that sprout vertically from the ground and a fungus found in tree sap in Northern Alberta.

“What is really fascinating is that despite these fungi looking so different, they have a lot in common at the level of their genomes,” says Spribille. “Nobody saw this coming.”

The researchers hypothesize that this group of fungi depend on other organisms to survive. “Their small genomes mean this class of fungi have lost much of their ability to integrate some complex carbohydrates,” said Spribille. “When we go back to look at each of these fungi, suddenly we see all of them are in a kind of symbiosis.”

The findings emphasize the need for broader study of fungal evolution, focusing particularly on how fungi inherit their biotechnological traits. The team also propose that the data could help support our understanding of previous extinction events in the fungi family tree: “We think it’s likely that the diversity we see today is just the tip of the iceberg that survived. And we don’t have that many examples of this kind of thing in fungi,” Spribille concludes.

Reference: Díaz-Escandón D, Tagirdzhanova G, Vanderpool D, et al. Genome-level analyses resolve an ancient lineage of symbiotic ascomycetes. Current Biology. doi: 10.1016/j.cub.2022.11.014.

This article is a rework of a press release issued by the University of Alberta. Material has been edited for length and content.