LOCALIZATION OF THE MATING-TYPE GENE IN AGARICUS-BISPORUS

The cultivated mushroom Agaricus bisporus is secondarily homothallic. Most basidia produce two basidiospores, each of which receives two of the four postmeiotic nuclei. Usually, the two packaged nuclei carry co mpatible mating types. Previous studies suggested that there may be on ly a single mating type locus in A. bisporus. In this study, we determ ined whether the mating type segregated as a single Mendelian determin ant in a cross marked with 64 segregating molecular markers. To score mating types, each of the 52 homokaryotic offspring from this cross wa s paired with each of the two progenitor homokaryons. Compatible matin gs were identified by the formation of genetically stable heterokaryon s which were verified by assay of restriction fragment length polymorp hisms (RFLPs). Data for screening mycelial interactions on petri plate s as well as fruit body formation were compared with the RFLP results. Mating types of 43 of the 52 homokaryotic offspring were determined o n the basis of RFLP analysis. Our results indicate (i) there is a segr egating mating type gene in A. bisporus, (ii) this mating type gene is on the largest linkage group (chromosome 1), (iii) mycelial interacti ons on petri plates were associated with heterokaryon formation under selected conditions, (iv) fruit body formation was dependent upon the mating type gene, and (v) compatible mating types may not always be su fficient for fruiting.