ISOLATION OF EXPRESSED SEQUENCE TAGS OF AGARICUS-BISPORUS AND THEIR ASSIGNMENT TO CHROMOSOMES

The genome of the cultivated basidiomycete Agaricus bisporus Horst U1 and of its homokaryotic parents has been characterized by using an opt imized method of pulsed-field gel electrophoresis. Expressed sequence tags obtained as expressed cDNAs from a primordial tissue-derived cDNA library and a number of previously isolated genes were used to identi fy the individual chromosomes of the parental lines of Horst U1. The g enome consists of 13 chromosomes, and its total size is 31 Mb. For tho se chromosomes that could not be resolved by contour-clamped homogeneo us electric field electrophoresis, the segregation of marker genes was studied in a set of 86 homokaryotic offspring of Horst U1. At least t wo markers were assigned to each individual chromosome. In this way al l individual chromosomes were unequivocally identified. The large size difference observed between the homologous chromosomes IX, harboring the rDNA repeat, was shown to be largely due to a higher copy number o f rDNA in parental strain H97 than in parental strain H39.