Role of peg formation in clamp cell fusion of homobasidiomycete fungi

Abstract

In most filamentous basidiomycetes, clamp cells are found at the septa of dikaryotic mycelia. Clamp cell formation starts at hyphal tip cells with the development of a lateral bulge at a position slightly apical to the future septum. Relative to the growth direction of the hypha, the protrusion expands backwards into a hook-like structure. Next, the two genetically different haploid nuclei within the hyphal tip cell divide. A septum appears between clamp cell and hyphal tip cell, thereby trapping one nucleus within the clamp cell. Another septum is laid within the hypha, separating a nucleus of the other type in the newly generated subapical hyphal cell from the two different nuclei kept together in the new apical hyphal cell. Through fusion of clamp and subapical cell, the two solitary nuclei become united within the subapical hyphal compartment. In 1933, Buller described subapical formation of a peg to which the clamp cell fuses as an additional, subsequently neglected step in this series of events. In this study, we represent evidence for subapical peg formation and its role in clamp cell fusion. Our observations potentially indicate a B mating type regulated extracellular communication between clamp and subapical hyphal cell.

Evolution of the Bipolar Mating System of the Mushroom Coprinellus disseminatus From Its Tetrapolar Ancestors Involves Loss of Mating-Type-Specific Pheromone Receptor Function

“…Transformants receiving both A and B mating type genes grow fluffy with some septa having fused clamp connections. At other septa, the apical cell displays an unfused clamp while the subapical side produces an enlarged peg (Kü es et al 1998(Kü es et al , 2002Badalyan et al 2004). Phenotypes of strain 218 transformants receiving C. disseminatus constructs 99.1Aa,16.3Aa,99.1Ab,or 98.2Ab were indistinguishable from phenotypes of transformants with native A mating-type genes ( Figure 7A).…”

“…Cotransformations used 1 mg DNA for each plasmid. Transformants were picked onto minimal medium (Granado et al 1997) and checked for A-regulated clamp cell production (Kü es et al 1992) and B-regulated subapical peg formation and clamp cell fusion (Badalyan et al 2004) under a microscope. Functional expression of pheromone receptor and/ or pheromone genes was further analyzed in mating reactions (O'Shea et al 1998) on YMG/T medium (Granado et al 1997) with monokaryon PS004-2 (A42, B1; P. Srivilai, unpublished data).…”

An Essential Gene for Fruiting Body Initiation in the Basidiomycete Coprinopsis cinerea Is Homologous to Bacterial Cyclopropane Fatty Acid Synthase Genes

“…Like homokaryon AmutBmut (Kertesz-Chaloupková et al 1998; Badalyan et al 2004), the mutant forms fused clamp cells at the hyphal septa and produces 10 9 oidia/ plate in a light-dependent manner, indicating that mating-type functions in mutant 6-031 are not affected. Mutant 6-031 forms primary hyphal knots in the dark that mature into sclerotia when cultures are further kept in the dark (not shown).…”

Basidiomycete Mating Type Genes and Pheromone Signaling

“…This includes the initial pairing of the haploid nuclei with different A and B specificities and the synchronous division of the nuclear pair in association with the initial development of the clamp cell, the hook formation. Different B genes are then needed for the fusion of the hook cell to the subapical cell, which completes the clamp connection formation (4,49,80) (Fig. 1).…”

“…(2) As a consequence of nuclear migration, multinucleate hyphae occur in the interaction zone of the mates. Unfused clamp connections (pseudoclamps) in the multinucleate hyphae are seen as a function of A-regulated development (3), which then controls the pairing of different nuclei followed by the hook cell formation and synchronous nuclear division (4). After separation of the sister nuclei, a cross wall is formed at the base of the hook and in the hypha (5).…”