XVI International Botanical Congess

Coprinus cinereus produces tetrads of spores. Basidial nuclei undergo two meiotic divisions, and each of the four products migrates into a spore. Mutants defective in meiosis, such as spo11-1 fail to undergo the meiotic divisions and produce white caps. spo11 encodes a type II topoisomerase which in other systems initiates DNA DSBs required for meiotic recombination. We screened for suppression of the spore formation defect. Oidia from the spo11-1 strain were mutagenized, and 5001 surviving colonies were collected. Mycelia were induced to fruit. Of the 1385 isolates that produced fruiting bodies, 8 produced grey caps. All 8 produced more spores than the spo11-1 mutant, and the percent viability of these spores was higher than that of the starting strain. Three strains formed dyads: two nuclei after meiosis, followed by two spores per basidiu.