The Assembled and Annotated Genome of the Fairy-Ring Fungus Marasmius oreades

Marasmius oreades is a basidiomycete fungus that grows in so called fairy rings, which are circular, underground mycelia common in lawns across temperate areas of the world. Fairy rings can be thought of as natural, long-term evolutionary experiments. As each ring has a common origin and expands radially outwards over many years, different sectors will independently accumulate mutations during growth. The genotype can be followed to the next generation, as mushrooms producing the sexual spores are formed seasonally at the edge of the ring. Here, we present new genomic data from 95 single-spore isolates of the species, which we used to construct a genetic linkage map and an updated version of the genome assembly. The 44-Mb assembly was anchored to 11 linkage groups, producing chromosome-length scaffolds. Gene annotation revealed 13,891 genes, 55% of which contained a pfam domain. The repetitive fraction of the genome was 22%, and dominated by retrotransposons and DNA elements of the KDZ and Plavaka groups. The level of assembly contiguity we present is so far rare in mushroom-forming fungi, and we expect studies of genomics, transposons, phylogenetics, and evolution to be facilitated by the data we present here of the iconic fairy-ring mushroom. Significance Genome assemblies of mushroom-forming fungi with complete chromosome sequences are currently rare, and the large clade of Marasmius is particularly undersampled, obstructing studies of genome evolution in this part of the fungal tree of life. Here, the nearly gapless chromosome and mitochondrion sequences of Marasmius oreades, commonly known as the Scotch bonnet or fairy-ring mushroom, are presented, alongside a high-quality gene annotation and repeat library. These data resources open up the opportunity to answer detailed questions about mushroom evolution.

Automated summary

Marasmius oreades, commonly known as the Scotch bonnet or fairy-ring mushroom, has a nearly gapless chromosome and mitochondrion sequences presented in this study, along with high-quality gene annotation and repeat library. These data resources provide an opportunity to answer detailed questions about mushroom evolution, as genome assemblies of mushroom-forming fungi with complete chromosome sequences are currently rare.