Control of basidiospore production by a nuclear gene in the fungus Coprinus congregatus

Summary The genetical control of basidiospore production by sporophores of the fungus Coprinus congregatus was studied. This species is characterized by a bipolar compatibility control, and homokaryons with complementary alleles A1 and A2 can be distinguished apart. We confirmed that the pale mushroom phenotype of the fungus is determined by a nuclear gene symbolized pal. This gene also controls a sporeless character and segregates independently of the mating-type locus. Dikaryons homoallelic for the pal^– allele produce typical pale and sporeless sporophores, while heteroallelic (pal⁺, pal^–) and homoallelic (pal⁺, pal⁺) dikaryons produce normal or almost normal sporulating sporophores. In order to segregate homokaryons homoallelic for the pal gene (A1, pal^–; A1, pal⁺, A2, pal^–; A2, pal⁺), the following protocols were used: (a) the dikaryotization of stock homokaryons containing the pal⁺ allele and of each mating type, A1 or A2, by dikaryotic mycelia homoallelic for the pal^– allele; (b) the culturing of homokaryotic mycelia issuing from the germination of basidiospores from sporophores produced by dikaryotic mycelia heterokaryotic for the pal gene; (c) the culturing of mycelia grown from protoplasts obtained from dikaryons homoallelic for the pal^– allele (D6 strain), and from homokaryons heteroallelic for the pal gene (H8), or homoallelic for pal^#x002B;+ allele (H7). These techniques enabled us to segregate homokaryons of the four types defined above and were indispensable in the segregation of the pal^– homoallelic homokaryons as no basidiospores were produced by typical pale mushrooms.