Another dark taxon comes to light: Semicentenialomycetes, a new class within the Pucciniomycotina (Basidiomycota), and its first described representative, Semicentenialea rex

Abstract

Only a small fraction of the global fungal diversity is described, and a large number of fungal sequences from environmental DNA (eDNA) lack relevant reference sequences for taxonomic identification in metabarcoding studies. Among these are several deeply divergent fungal lineages, hypothesized to be class- and order-level lineages, currently known only by eDNA sequences. Here, we formally describe the first representative of one such lineage, previously referred to as Clade GS 25, now captured in culture.

We use a phylogenomic approach to test the phylogenetic placement and taxonomic rank hypothesized for this lineage and present the formally described Semicentenialea rex sp. nov. as the first known species in the novel class Semicentenialomycetes (Pucciniomycotina, Basidiomycota). Semicentenialea rex sp. nov. was isolated from pine roots taken from a podzol soil profile in a pine forest in central Sweden and shows an affinity to mineral soil horizons in this habitat.

The same species was isolated independently from pine roots collected in central Finland. Additionally, we provide the first phylogenomic resolution of Pucciniomycotina, using reference genomes from all described classes with the exception of Cryptomycocolacomycetes. In addition to expanding our knowledge about the diversity of Pucciniomycotina, our study highlights the importance of continued culturing efforts in combination with eDNA studies to uncover hidden fungal diversity.

Furthermore, our data provide insights into the strengths and limitations associated with amplicon sequence variants, different similarity cut-offs, and genome-derived ribosomal operons.