Mating-type genes and hyphal fusions in filamentous basidiomycetes

From dikaryon to diploid

“…In C. cinerea the nuclei maintain a distance of 15e20 mm from each other (Kamada et al, 1993), whereas in S. commune they appear to be closer (Schuurs et al, 1998). Movement of the migrant nucleus through the cells of the recipient hypha requires partial dissolution of the dolipore septum (Casselton et al, 1971;Giesy and Day, 1965;Raudaskoski, 1998Raudaskoski, , 2015, which is the characteristic septum of fungi in the Agaricomycotina (see for example, Moore and McAlear, 1962;M€ uller et al, 2000;Orlovich and Ashford, 1994;Raudaskoski, 1998;van Driel et al, 2009). Paired nuclei in the tip cell divide in synchrony.…”

“…Recognition of different mating type alleles occurs intracellularly after cell fusion. Once a bridge is established between compatible hyphae, a reciprocal exchange of nuclei occurs, and the migrant nucleus from one mate moves to the tip cell of the recipient mate, where it pairs with the resident nucleus, establishing the dikaryon (Raudaskoski, 1998(Raudaskoski, , 2015. In C. cinerea the nuclei maintain a distance of 15e20 mm from each other (Kamada et al, 1993), whereas in S. commune they appear to be closer (Schuurs et al, 1998).…”

“…Next, the clamp cell fuses with the subapical cell forming a clamp connection and delivers the nucleus to the subapical cell restoring the dikaryotic state to this cell. The cross walls separating the apical, subapical, and clamp cell contain dolipore septa (Raudaskoski, 2015). Early researchers realized that there was a close association between the synchronous division of nuclei in the apical cell and the formation of clamp connections, although, they also recognized that exceptions exist in which nuclear division of a dikaryon occurs in the absence of clamp connections (Raper, 1966).…”

“…Nuclear migration, septum dissolution and fusion of the clamp cell (hook) with the subapical cell are controlled by the B locus. Pairing of nuclei, conjugate division, and clamp cell formation are controlled by the A locus (Casselton and Olesnicky, 1998;K€ ues et al, 2011;Raper, 1966;Raudaskoski and Kothe, 2010;Stankis and Specht, 2007). Transcriptome analysis of strains with an active A, active B, or active A and B has led to identification of genes differentially regulated in each of these pathways (Erdmann et al, 2012).…”

“…In the latter case, the nuclei may have the same or different genotype at the mating type loci (Hibbett et al, 1994;Raper, 1966). Cell fusion and karyogamy are temporally and spatially separated in the life cycle of the majority of basidiomycete fungi, exemplified by Coprinopsis cinerea and Schizophyllum commune, which have long been used as model organisms for studies, among others, on mating type determination, fruiting body development, and somatic recombination (Casselton and Olesnicky, 1998;K€ ues, 2000;Papazian, 1954;Parag, 1962;Raper, 1966;Raudaskoski and Kothe, 2010;Stankis and Specht, 2007).…”