No 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.

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In this paper we describe the initial genetic analysis of some developmental REMI and UV mutants of the selfcompatible homokaryon Amut Bmut. We show that such homokaryons can mate with each other although in fruitbodies we often found spores of only one parent. Crosses with monokaryons of different mating types gave some indications about numbers of mutations and linkage of genetic markers. In most cases, however, we observed an uneven distribution of markers, most likely because of loss of certain progeny. Our results necessitate the construction of monokaryons as closely related to homokaryon AmutBmut as possible but with different mating type loci.

Plasmids usually integrate ectopically into the genome of the homobasidiomycete Coprinus cinereus in transformations. Often, integration occurs at multiple sites indicating that more than one plasmid copy was incorporated. This feature prompted us to study transformation with mixtures of several different plasmids in several genetic backgrounds. We found multiple cotransformation to be efficient even with four different plasmids. Simultaneous uptake of a second plasmid was between 5-55%, of two additional plasmids between 3-18% and 3% for three additional plasmids. These high frequencies make possible the analysis of interactions between different heterologous genes introduced into the same nucleus.