We have constructed a genetic linkage map of the edible basidiomycete Pleurotus ostreatus (var. Florida). The map is based on the segregation of 178 random amplified polymorphic DNA and 23 restriction fragment length polymorphism markers; four hydrophobin, two laccase, and two manganese peroxidase genes; both mating type loci; one isozyme locus (est1); the rRNA gene sequence; and a repetitive DNA sequence in a population of 80 sibling monokaryons. The map identifies 11 linkage groups corresponding to the chromosomes of P. ostreatus, and it has a total length of 1,000.7 centimorgans (cM) with an average of 35.1 kbp/cM. The map shows a high correlation (0.76) between physical and genetic chromosome sizes. The number of crossovers observed per chromosome per individual cell is 0.89. This map covers nearly the whole genome of P. ostreatus.Pleurotus ostreatus (oyster mushroom) is an edible mushroom that occupies the second most important position in the world mushroom market, led by the button mushroom Agaricus bisporus (5, 49). Besides its importance for food production, P. ostreatus is interesting for applications such as paper pulp bleaching, cosmetics, and the pharmaceutical industry. These different applications have fueled research on specific aspects of Pleurotus biochemistry and molecular biology (4,8,20,(31)(32)(33)(34)42).Despite its economic importance, only a limited number of genetic studies of P. ostreatus have been done because of the difficulty in performing directed crosses between strains, contradictory data about the size and organization of its genetic material, and the lack of a genetic linkage map for it. Moreover, breeding of new P. ostreatus strains with a higher agricultural or industrial value has been traditionally carried out by trial and error because of the aforementioned reasons (2).In order to facilitate the design of programs aimed to improve the strains currently available, it is important to increase our knowledge of the genome organization of this fungus. However, the study of the organization of the P. ostreatus genome has been hampered by the small size of fungal chromosomes and by the occurrence of intranuclear mitosis (15). Different authors have reported different chromosome numbers for this species (15,41,51), and only recently has this number been determined using pulsed-field gel electrophoresis (32). This species contains 11 chromosomes that account for a total genomic size of about 35.1 Mbp per haploid genome. Furthermore, chromosome length polymorphisms occur between the homologous chromosomes present in each of the two nuclei in the dikaryon. Electrophoretic separation of P. ostreatus chromosomes allowed the physical mapping of some genes or phenotypic markers on specific chromosomes (for instance, the A mating locus physically mapped on chromosome III and the B locus was on chromosome IX) (32).The use of molecular markers combined with the construction of linkage maps is a potent strategy for designing breeding strategies and for attempting positional cloning of genes ...

Pleurotus ostreatus is a hetertothallic homobasidiomycete whose mating is controlled by a bifactorial tetrapolar genetic system. Although this mechanism is well accepted, there is a lack of knowledge about its molecular basis, as the incompatibility loci have not been cloned and sequenced. As a first step towards the elucidation of the molecular structure of the A-type incompatibility locus, molecular markers have been isolated which correspond to genomic sequences present in different strains of P. ostreatus but not in other higher basidiomycetae. These markers reveal single-copy genetic regions in which some degree of genetic variability can be detected.

The white rot fungus Pleurotus ostreatus is an edible basidiomycete with increasing agricultural and biotechnological importance. Genetic manipulation and breeding of this organism are restricted because of the lack of knowledge about its genomic structure. In this study, we analyzed the genomic constitution ofP. ostreatus by using pulsed-field gel electrophoresis optimized for the separation of its chromosomes. We have determined that it contains 11 pairs of chromosomes with sizes ranging from 1.4 to 4.7 Mbp. In addition to chromosome separation, the use of single-copy DNA probes allowed us to resolve the ambiguities caused by chromosome comigration. When the two nuclei present in the dikaryon were separated by protoplasting, analysis of their karyotypes revealed length polymorphisms affecting various chromosomes. This is, to our knowledge, the clearest chromosome separation available for this species.

The switch from budding to filamentous growth is a key aspect of invasive growth and virulence for the fungal phytopathogen Ustilago maydis. The cyclic AMP (cAMP) signaling pathway regulates dimorphism in U. maydis, as demonstrated by the phenotypes of mutants with defects in protein kinase A (PKA). Specifically, a mutant lacking the regulatory subunit of PKA encoded by the ubc1 gene displays a multiple-budded phenotype and fails to incite disease symptoms, although proliferation does occur in the plant host. A mutant with a defect in a catalytic subunit of PKA, encoded by adr1, has a constitutively filamentous phenotype and is nonpathogenic. We employed serial analysis of gene expression to examine the transcriptomes of a wild-type strain and the ubc1 and adr1 mutants to further define the role of PKA in U. maydis. The mutants displayed changes in the transcript levels for genes encoding ribosomal proteins, genes regulated by the b mating-type proteins, and genes for metabolic functions. Importantly, the ubc1 mutant displayed elevated transcript levels for genes involved in phosphate acquisition and storage, thus revealing a connection between cAMP and phosphate metabolism. Further experimentation indicated a phosphate storage defect and elevated acid phosphatase activity for the ubc1 mutant. Elevated phosphate levels in culture media also enhanced the filamentous growth of wild-type cells in response to lipids, a finding consistent with PKA regulation of morphogenesis in U. maydis. Overall, these findings extend our understanding of cAMP signaling in U. maydis and reveal a link between phosphate metabolism and morphogenesis.Development and virulence are regulated by cyclic AMP (cAMP)/protein kinase A (PKA) and mitogen-activated protein (MAP) kinase signaling pathways in several fungi, including the corn smut pathogen Ustilago maydis (13,38,46). Mating of haploid U. maydis cells, which are nonpathogenic and yeast-like, leads to the formation of infectious, dikaryotic hyphae. This process is regulated by two unlinked mating-type loci, a and b. Cell recognition and fusion of conjugation tubes are controlled by the a mating-type locus encoding a pheromone (mfa)-pheromone receptor (pra) system that acts through a conserved MAP kinase module (8). Several components of the MAP kinase module have been identified, including the MAP kinase kinase kinase Ubc4, the MAP kinase kinase Fuz7/Ubc5, the MAP kinase Ubc3/Kpp2, and the putative adaptor protein Ubc2 (1,5,(46)(47)(48)50).