Agaricus bisporus is the model fungus for the adaptation, persistence, and growth in the humic-rich leaf-litter environment. Aside from its ecological role, A. bisporus has been an important component of the human diet for over 200 y and worldwide cultivation of the “button mushroom” forms a multibillion dollar industry. We present two A. bisporus genomes, their gene repertoires and transcript profiles on compost and during mushroom formation. The genomes encode a full repertoire of polysaccharide-degrading enzymes similar to that of wood-decayers. Comparative transcriptomics of mycelium grown on defined medium, casing-soil, and compost revealed genes encoding enzymes involved in xylan, cellulose, pectin, and protein degradation are more highly expressed in compost. The striking expansion of heme-thiolate peroxidases and β-etherases is distinctive from Agaricomycotina wood-decayers and suggests a broad attack on decaying lignin and related metabolites found in humic acid-rich environment. Similarly, up-regulation of these genes together with a lignolytic manganese peroxidase, multiple copper radical oxidases, and cytochrome P450s is consistent with challenges posed by complex humic-rich substrates. The gene repertoire and expression of hydrolytic enzymes in A. bisporus is substantially different from the taxonomically related ectomycorrhizal symbiont Laccaria bicolor . A common promoter motif was also identified in genes very highly expressed in humic-rich substrates. These observations reveal genetic and enzymatic mechanisms governing adaptation to the humic-rich ecological niche formed during plant degradation, further defining the critical role such fungi contribute to soil structure and carbon sequestration in terrestrial ecosystems. Genome sequence will expedite mushroom breeding for improved agronomic characteristics.
Mushrooms, such as Coprinus cinereus, possess large families of pheromones and G-protein-coupled receptors that are sequestered at the B mating-type locus and whose function is to confer vast numbers of different mating types. This ability results from complex patterns of cognate and noncognate pheromone/ receptor pairings, which potentially offer a unique insight into the molecular interaction between receptor and ligand. In this study we have identified many more members of these families by molecular analysis of strains collected worldwide. There are three groups of genes at each B locus. We have identified two alleles of group 1, five alleles of group 2, and seven alleles of group 3, encoding in total 14 different receptors and 29 different pheromones. The specificity of many newly identified alleles was determined by transformation analysis. One striking finding was that receptors fall into groups based on sequence homology but these do not correspond to the groups defined by position, indicating that complex evolutionary processes gave rise to the B loci. While additional allelic versions may occur in nature, the number of B specificities possible by combination of the alleles that we describe is 70, close to previous estimates based on population analysis. T HE role of pheromone signaling in fungal matingand receptors were first identified as mating-type deterhas largely been elucidated from studies of the budminants and map to what has been designated the B ding yeast Saccharomyces cerevisiae. This fungus has just mating-type locus. A second mating-type locus, A, entwo mating types and pheromones are secreted to act codes the subunits of a transcription factor belonging as chemoattractants for identifying compatible mating to the homeodomain family (Kü es et al. 1994a) that is partners. Binding of a pheromone to an appropriate necessary, together with pheromone signaling, to proreceptor on the cell surface triggers an intracellular mote the initial stages of sexual development. Compati-G-protein-linked MAP kinase cascade that results in ble A genes encode versions of the proteins that can changes in growth direction to permit cell fusion, which heterodimerize following cell fusion, an interaction that is then followed immediately by nuclear fusion (reis analogous to that between the MATa1 and MAT␣2 viewed by Kurjan 1993). Once cells are diploid, pheromating-type proteins in mated cells of S. cerevisiae (remone signaling ceases.viewed by Johnson 1995). Pheromone signaling also plays an essential role in In contrast to S. cerevisiae, compatible cell fusion in mating in basidiomycete fungi (reviewed by Casselton C. cinereus is not followed immediately by nuclear fusion, and Olesnicky 1998), but in mushroom species such as but by an extended vegetative phase in which the nuclei Coprinus cinereus, unlike S. cerevisiae, there is no evidence from each mate remain paired in each cell, a phase that pheromones have a role in mate attraction (Olesknown as the dikaryophase or dikaryon. The B matingnicky et ...
Double-stranded RNA (dsRNA) has been isolated from Agaricus bisporus fruit bodies exhibiting a wide range of disease symptoms. The symptoms which occurred singularly or in combination included ; bare cropping areas on commercial beds (primordia disruption), crop delay, premature veil opening, off-or brown-coloured mushrooms, sporophore malformations and loss of crop yield. All symptoms were associated with loss of yield and/or product quality. Collectively, these symptoms are described as mushroom virus X (MVX) disease. The dsRNA titre was much lower than that previously encountered with the La France viral disease of mushrooms and a modified cellulose CF11 protocol was used for their detection. A broad survey of cultivated mushrooms from the British industry identified dsRNA elements ranging between 640 bp and 20.2 kbp; the majority have not previously been described in A. bisporus. 26 dsRNA elements were identified with a maximum of 17, apparently non-encapsidated dsRNA elements, in any one sample. Three dsRNAs (16.2, 9.4 and 2.4 kbp) were routinely found in mushrooms asymptomatic for MVX. Previously, La France disease was effectively contained and controlled by minimising the on-farm production and spread of basidiospores. Our on-farm observations suggest that MVX could be spread by infected spores and/or mycelial fragments.
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