The phase change from vegetative to reproductive growth in Agaricus\ud bisporus is a complex process involving changes in morphology at least in part\ud regulated genetically and influenced by various environmental signals. This work\ud was aimed at understanding how the morphology changes, and the specific\ud environmental parameters are involved, and which genes show changes in\ud transcription during the phase change process in A. bisporus.\ud Different resources and methodologies were developed and applied to\ud investigate this process including digital time-lapse photography, genome database\ud assembly, design, validation and normalisation of a custom oligonucleotide gene\ud expression microarray and analysis of microarray-generated gene expression profiles\ud showing the response of this fungus under stimulatory and non-stimulatory\ud environmental conditions.\ud Key stages that occur during reproductive differentiation and development\ud were identified and defined. It was found that temperature and the mushroom\ud volatile, 1-octen-3-ol, act as an on/off switches as they block specific stages of the\ud phase change while carbon dioxide acts as a quantitative regulator as high amounts\ud of this molecule reduce the number of primordia and fruit bodies that develop.\ud Gene expression profiles were constructed showing the changes in gene\ud expression in peat-based A. bisporus samples, grown under commercial cultivation\ud conditions which were designed to stimulate reproductive growth, and experimental\ud cultivation conditions which were designed to separate out the effects of the three\ud environmental parameters mentioned previously. It was found that 52 genes were\ud differentially expressed in A. bisporus during the phase change from vegetative\ud mycelium into fruit body primordia. A comparison with the gene expression profiles\ud constructed for the experimental growth conditions, in correlation with\ud morphological observations enabled the separation of these 52 genes into 3 clusters.\ud One cluster contained 4 genes that are likely to be involved in the regulation of the\ud “early” phase change, a second cluster contained 11 genes that are likely to be\ud involved in the regulation of the “late” phase change and the third cluster contained\ud 37 genes that are likely to be involved with physiological processes supporting the\ud phase change
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