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The Cys2His2 zinc finger protein gene c2h2 of Schizophyllum commune is involved in mushroom formation. Its inactivation results in a strain that is arrested at the stage of aggregate formation. In this study, the c2h2 orthologue of Agaricus bisporus was over-expressed in this white button mushroom forming basidiomycete using Agrobacterium-mediated transformation. Morphology, cap expansion rate, and total number and biomass of mushrooms were not affected by over-expression of c2h2. However, yield per day of the c2h2 over-expression strains peaked 1 day earlier. These data and expression analysis indicate that C2H2 impacts timing of mushroom formation at an early stage of development, making its encoding gene a target for breeding of commercial mushroom strains.

Recent genome-wide studies have demonstrated that fungi possess the machinery to alternatively splice pre-mRNA. However, there has not been a systematic categorization of the functional impact of alternative splicing in a fungus. We investigate alternative splicing and its functional consequences in the model mushroom forming fungus Schizophyllum commune. Alternative splicing was demonstrated for 2,285 out of 12,988 expressed genes, resulting in 20% additional transcripts. Intron retentions were the most common alternative splicing events, accounting for 33% of all splicing events, and 43% of the events in coding regions. On the other hand, exon skipping events were rare in coding regions (1%) but enriched in UTRs where they accounted for 57% of the events. Specific functional groups, including transcription factors, contained alternatively spliced genes. Alternatively spliced transcripts were regulated differently throughout development in 19% of the 2,285 alternatively spliced genes. Notably, 69% of alternatively spliced genes have predicted alternative functionality by loss or gain of functional domains, or by acquiring alternative subcellular locations. S. commune exhibits more alternative splicing than any other studied fungus. Taken together, alternative splicing increases the complexity of the S. commune proteome considerably and provides it with a rich repertoire of alternative functionality that is exploited dynamically.

Establishment of the dikaryotic mycelium and formation of fruiting bodies are highly complex developmental programmes that are activated by a combination of environmental cues. A wide variety of proteins are expected to regulate and coordinate these programmes or to fulfil enzymatic conversions or structural roles. With the identification of the first genes involved in mushroom development, we are only at the beginning of understanding fruiting body formation. The process of identification of genes will be accelerated by whole genome expression studies and increased availability of molecular tools to assign functions to genes. Establishment of the dikaryon and emergence of fruiting bodies in basidiomycetes are regulated by the mating-type genes. These genes encode DNA-binding proteins and pheromones and their receptors. Regulation of fruiting by the mating-type genes is mediated by downstream transcription factors. Several genes encoding such regulatory proteins have now been identified. Regulatory circuits ultimately activate genes encoding structural proteins or enzymes that are involved in fruiting body formation. The role of hydrophobins is well established. They enable hyphae to escape the aqueous environment to allow fruiting body development. Moreover, they coat aerial structures and line air channels in mushrooms. The hydrophobic coating irreversibly directs growth of hyphae into the air, allows dispersal of spores and ensures gas exchange in fruiting bodies under humid conditions. Apart from hydrophobins, phenolics polymerised by the action of laccases may contribute to surface hydrophobicity of fruiting bodies. These enzymes have also been proposed to cross-link cell walls of hyphae in the fruiting bodies but this still has to be established. Experimental evidence indicates that cytochrome P450 enzymes, lectins, haemolysins and expansins also function in mushroom development. Lectins may be involved in aggregation of hyphae, haemolysins in signalling p