Snowball-like mushroom morphologies and a novel gene family required for fruiting body development

The morphogenesis of sexual fruiting bodies of fungi is a complex process determined by a genetically encoded programme. Fruiting bodies reached highest complexity levels in the Agaricomycetes, yet, the underlying genetics is currently poorly known. In this work, we functionally characterised an unannotated gene we term snb1, whose expression level increases rapidly during fruiting body initiation. According to phylogenetic analyses, orthologues of snb1 are present in almost all Agaricomycetes and may represent a novel conserved gene family that plays a substantial role in fruiting body development. We disrupted snb1 using CRISPR/Cas9 in the agaricomycete model organism Coprinopsis cinerea. Snb1 mutants formed unique, snowball-shaped, rudimentary fruiting bodies that could not differentiate caps, stipes and lamellae. We took advantage of this phenotype to study fruiting body differentiation using RNA-Seq analyses. This revealed a multitude of differentially regulated genes and gene families that may be related to tissue differentiation and the formation of structures. Taken together, the novel gene family of snb1 and the differentially expressed genes in the snb1 mutants provide valuable insights into the complex mechanisms underlying tissue differentiation in the Agaricomycetes. Wild type Coprinopsis cinerea (AmutBmut1) and snb1 knock out mutant strains were sampled for RNA sequencing. From both strains, samples were collected after 24 h (secondary hyphal knots) and 48 h (stage 1 primordia) post-light induction. Each sample group contains three biological replicates.