Common-B Heterokaryosis and Fruiting in Schizophyllum commune

Abstract

Common-B hetero-karyons (A1 Bl : A2 Bl) of S. commune Fr. (Fungi: Basidio-mycetes) were established by 3 methods: (1) illegitimate Buller phenomenon (di-mon matings); (2) direct isolation of heterokaryotic hyphae under the microscope; (3) mating auxotrophs with complementary nutritional requirements and selection of the prototrophic hetero-karyon on minimal medium. Small plugs of mycelium taken from matings of (3) gave growth on minimal medium only when taken from the region of confrontation of the 2 mycelia; nuclear migration either does not occur or it is restricted to a distance of no more than 2mm. In all the studied heterokaryons the septa are provided with pseudoclamps, which start their development like clamp connections of dikaryons but whose tips fail to fuse with the corresponding proximal cells. A pseudo-clamp has either no nucleus or 1 nucleus; it may develop into a side branch which grows backwards and in turn carries pseuoclamps. The apical cells are uni- or binucleate (rarely multinucleate), the rest uninucleate. The progeny of a common -B fruit body showed segregation, independent assortment, and linkage for 5 markers as expected from meiosis. It thus appears that the sexual process sensu stricto (i.e., karyogamy and meiosis) is not blocked by the incompatibility conferred by the B-homozygosity. The lack of any breakdown of 1 of the heterokaryons following maceration and other results, suggest that at least in this common-B mycelium the 2 genomes exist within 1 uninucleate cell. It is, therefore, possible that this mycelium is diploid.