The exp1 gene essential for pileus expansion and autolysis of the inky cap mushroom Coprinopsis cinerea (Coprinus cinereus) encodes an HMG protein.

The homobasidiomycete Coprinopsis cinerea is a member of the fungi known as inky cap mushrooms, and its fruiting-body pileus autolyzes soon after completion of the development. During the last 3h of the development, the pileus exhibits umbrella-like expansion: the pileal tissue is cracked at the base of each gill and then each gill tissue is split to form a V-shape, as seen in a cross section. We identified two C. cinerea mutants defective in both pileus expansion and autolysis. The defects in both mutants are due to recessive mutations in a single gene, designated exp1. The exp1 gene is predicted to encode an HMG1/2-like protein with two HMG domains. The transcription of exp1 is strongly induced in the pileus 3h before pileus expansion. This result, together with the fact that the exp1 mutations cause a specific developmental phenotype, suggest that Exp1 is a novel, transcriptional regulator controlling the final phase of fruiting-body morphogenesis.

Identification and characterisation of structural maintenance of chromosome 1 (smc1) mutants of Coprinopsis cinerea.

A Coprinopsis cinerea homokaryotic fruiting strain was mutagenised, identifying a mutant that exhibited a hyphal growth temperature sensitive defect and hyphal knot development defect at an early fruiting stage, even at the hyphal growth permissive temperature. Microscopic observation suggested that the mutant nuclei exhibited defects in the metaphase to anaphase transition at the restrictive temperature. The gene in which the mutation occurred was cloned, sequenced and determined to be homologous to smc1. Sequence analyses of the mutant revealed deletion of 28 base pairs in the 19th intron of the Cc.smc1 gene, resulting in complete failure of splicing of that intron and in insertion of 14 amino acids in the C-terminal region of the Cc.Smc1 protein. We isolated eight hyphal growth revertants and identified four intragenic suppressors. All were the result of amino acid substitutions in the C-terminal region. Three of the suppressors caused reversion of the arrest in an early fruiting stage. One of the suppressors exhibited cold sensitivity and failed to suppress the fruiting defect, suggesting that flexibility of a lobe in the C-terminal region is important for proper function of Cc.Smc1.

A linkage map of the basidiomycete Coprinus cinereus based on random amplified polymorphic DNAs and restriction fragment length polymorphisms.

A genetic linkage map of the basidiomycete Coprinus cinereus was constructed on the basis of the segregation of 219 RAPD markers, 28 RFLP markers and the A and B mating-type loci among 40 random basidiospore progeny from a single cross between a wild-type homokaryon, KF(3)#2, and an AmutBmut strain, #326. Thirteen linkage groups covering a total of 1346cM were identified and correlated to the 13 chromosomes of this fungus by hybridization of RFLP and RAPD marker probes to CHEF blots. These probes also revealed chromosome length polymorphisms (CLP), which could be associated with haplotype plots of the progeny. The average kb/cM ratio in this cross was approximately 27.9kb/cM. The AmutBmut strain undergoes sexual development without mating, because of mutations in both A and B mating-type loci, and has been used to identify mutations affecting developmental processes such as dikaryosis, fruit body morphogenesis, and meiosis. The markers in the map, especially the RAPD ones, would facilitate mapping of genes responsible for such mutations induced in the AmutBmut strain.