Molecular aspects of growth and fruiting of the edible mushroom Agaricus bisporus

Abstract

Contains fulltext : 18664.pdf (publisher's version ) (Open Access)The research described in this thesis was part of a project aimed at the isolation of marker genes and the development of a genetic map of the white button mushroom Agaricus bisporus. The thesis concentrates on molecular aspects of growth and fruiting of A. bisporus. In order to study the genetic processes that are involved in fruiting of A. bisporus, we focused on the cloning and characterisation of genes that are specifically expressed during fruit body development and maturation. Two fruit body specific genes identified by differential screening techniques appeared to encode small hydrophobic cell wall proteins belonging to the fungal family of surface-active hydrophobins. One of those proteins, HYPA, is part of a protective layer surrounding the mushroom caps. It showed, like other fungal hydrophobins, a self-assembling behaviour which was shown by in vitro studies using Atomic Force Microscopy. Additionally, to study genetic aspects of compost utilisation by A. bisporus, we aimed at the cloning of genes involved in the release of sugars from the plant polysaccharides present in compost. Cloning and characterisation of one of such genes, the xlnA gene encoding an endo-1,4-`-xylanase, gave us a better insight in the regulation of enzymes that can degrade lignocellulosic compounds of compost. Expression studies with xlnA and cel3, encoding a cellobiohydrolase, showed that both genes are strongly induced on compost and the regulation of their transcription seems to be an elegant example of adaptation of a fungus to its natural niche. Furthermore, experiments were focused on the isolation and characterisation of housekeeping genes. Cloning of the housekeeping genes pgkA, pkiA and aldA enabled us to compare the structure of A. bisporus genes with homologous genes of related organisms and to monitor their expression in different parts of mature mushrooms. The cloning of large number of genes combined with chromosome separation techniques forms a solid base for the development of a gene-based linkage map and will make A. bisporus more amenable for breeding purposes191 p