Genetics of secondarily homothallic basidiomycetes

Abstract

SUMMARYThe random migration of meiotic products to give binucleate spores in secondarily homothallic basidiomycetes gives frequencies of nuclear association which have not previously been recognised.For a single segregating factor in two-spored species, the probability of a basidiospore receiving unlike nuclei is twice that of it receiving like nuclei.Consequently random spore progenies can be expected to yield genotypic ratios of 1:4: 1 with the heteroallelic class predominating. If eight nuclei are present in the basidia of four-spored species then random migration would favour unlike over like pairing in the proportion 4:3; this would give a genotypic ratio of 3 :8:3. Extrapolations are made for two and n factors, and the expected phenotypic ratios for mating-type factors, auxotrophic markers and sporophore characters are derived. Second division segregation and chromosome mapping are also considered.Random nuclear migration in secondarily homothallic basidiomycetes favours heteroallelism and provides a simple explanation for the regularly observed preponderance of isolates heteroallelic for mating-type.

Spore behaviors reveal a category of mating-competent infertile heterokaryons in the offspring of the medicinal fungus Agaricus subrufescens

“…This represents the rate of loss of parental heterozygosity at this locus. Different rates of homoallelism have been considered (for the history, see Challen and Elliott 1989) until Langton and Elliott (1980) re-interpreted the consequence of random migration in pseudohomothallism. In a bisporic random model (i.e., four meiotic products migrating at random in two spores), the theoretical rate is 1/3 (Langton and Elliott 1980).…”

“…Different rates of homoallelism have been considered (for the history, see Challen and Elliott 1989) until Langton and Elliott (1980) re-interpreted the consequence of random migration in pseudohomothallism. In a bisporic random model (i.e., four meiotic products migrating at random in two spores), the theoretical rate is 1/3 (Langton and Elliott 1980). In the tetrasporic random model, a 3/7 rate of homoallelism at any locus had been proposed by Langton and Elliott (1980).…”

“…In a bisporic random model (i.e., four meiotic products migrating at random in two spores), the theoretical rate is 1/3 (Langton and Elliott 1980). In the tetrasporic random model, a 3/7 rate of homoallelism at any locus had been proposed by Langton and Elliott (1980). However, taking in consideration the fact that 1/7 of these spores are true homokaryons since they receive nuclei from the same postmeiotic mitosis as represented in Fig.…”

Strain improvement in the cultivated mushroom Agaricus bisporus

“…and contrasting mating-type has been attributed to the non-random alignment of the meiotic spondles (EVANS, 1959) . It could also result quite simply from the random migration of the meiotic products to give binucleate spores (LANGTON & ELLIOTT, 1980) . Whatever the mechanism, the self-fertility of single spores promotes a `closed' life-cycle and imposes a degree of inbreeding .…”

Gene segregation in the two-spored basidiomycete Coprinus bilanatus

“…Evans (1953) working with the cultivated mushroom noted that the second meiotic spindles were often crossed and orientated in line with the long axis of the basidium. Langton and Elliott (1980) suggested that the dikaryotic spores were formed as a result of the random association of two of the four meiotic products into each spore. They noted that the random migration of the nuclei into the two spores would result in 2/3rds of the spores being dikaryotic.…”