Fruiting body development in the Basidiomycete Coprinopsis cinerea

Fruiting body development in Coprinopsis cinerea follows a conserved scheme defined by day and night phases, with well predictable distinct stages over the time. Fruiting starts with primary hyphal knot (PHK) formation in the dark, followed by light-induced compact aggregates, secondary hyphal knots (SHKs) in which stipe and cap tissues differentiate. Primordium development (P1 to P5) takes five days to culminate on day 6 of development in karyogamy, meiosis and subsequent basidiospore production which parallel fruiting body maturation. Development is regulated at distinct steps by light, temperature, humidity, nutrients, CO₂ and metals like copper. Light signals induce formation of SHKs, differentiation of tissues within the growing primordia, and karyogamy. Without light, ‘dark stipes’ are formed from SHKs with elongated stipes and underdeveloped caps. Copper addition has the same effect in all conditions. Lack of aeration before light-induced formation of SHKs fully blocks fruiting. When SHKs have been formed prior to blockage of air, development arrests. Block in aeration at P1 to P3 leads in light to outgrowth of ‘dark stipe’-like structures. When plates are air-sealed at the P4 or P5 fruiting body maturation happens with reduced sporulation. Mutants in light reception can form ‘dark stipes’ in light while the phenotype in others may arise from defects in regulation by aeration. Most mutants in fruiting are however simply blocked at specific steps. In a collection of about 1500 strains, mutations did not evenly distribute over the complete pathway. High numbers of mutants are available in hyphal know formation, comparably few in the subsequent steps up to P3. Larger sets of mutants exist for P4 and P5 when karyogamy and meiosis have to occur in the basidia and fruiting body maturation has to be initiated. Mutant numbers may reflect the genetic complexity of specific steps in fruiting.