The Agaricus genome project
An international consortium of scientists from seven countries has been working to complete the sequencing and analyses of the Agaricus bisporus genome. The genome sequencing was funded by the USA’s Department of Energy, the Joint Genome Initiative and the Community Sequencing Program; transcriptomic data were provided by the UK’s Horticultural Development Company (HDC) and the Institut National de la Recherche Agronomique (INRA) of France funded much of the bioinformatics analysis. The first release of the genome sequence was made in 2010 and the scientific paper on the sequence and analysis was published in 2012. The genomes of two A. bisporus strains were sequenced, one a cultivated European strain and the other isolated from the Sonoran Desert in California, USA. These genomes code for 10,438 and 11,289 protein-coding genes respectively. Analyses of the two genomes reveal that they contain the necessary genes for the degradation of polymers (lignin, cellulose, hemicellulose and proteins) found in dead plant material (e.g. leaves and wood); however this fungus grows poorly on dead leaves unless they are already partially decomposed. Further analysis of the genome and transcriptome (which genes expressed, where and when) offers a molecular explanation of how A. bisporus grow in the specific niche of partially decomposed humic-rich leaves. Compared with other wood- or leaf-degrading fungi, A. bisporus has a larger number of genes specialising in metabolising the toxic breakdown products of lignin and these genes are ‘switched on’ in the presence of humic substances. This has led to a proposal for a new econutritional classification of fungi degrading humified dead plant material as ‘humicolous’. The humic niche has environmental importance beyond mushroom cultivation. Humic substances are a major component of soil organic matter, so important for soil structure, water- and nutrient-holding characteristics, and humus also represents a large proportion of global sequestered carbon, important in carbon cycling and climate change.