Asexual sporulation in coprinus cinereus: structure and development of oidiophores and oidia in an amut bmut homokaryon

Polak, E., Hermann, R., Kues, U., and Aebi, M. 1997. Asexual sporulation in Coprinus cinereus: Structure and development of oidiophores and oidia in an Amut Bmut homokaryon. 22, 112-126. Coprinus cinereus strain AmutBmut is a homokaryon with mutations in both mating type loci. It produces asexual spores (oidia) in sticky liquid droplets on specialized aerial structures (oidiophores). These oidiophores have uninucleate cells and are organized as those of the monokaryon 5026 from which the strain derived. However, unlike in the monokaryon, oidiophores in strain AmutBmut are induced by light. Young oidiophores are easily detected upon light induction and the process of oidiophore development is readily followed in this strain. Fully grown oidiophores consecutively give rise to short branches (oidial hyphae) that break up into two or occasionally three uninucleate oidia (arthroconidia) until up to 200 oidia are collected at the tip of the oidiophore. Mature spores are enclosed by a mucilage and a double-layered primary cell wall with hair-like structures except for the sides of former cell attachments. In a summary of our microscopic observations on developing oidiophores and nuclear stainings we present a model showing the successive steps of oidiophore and spore development.

The origin of multiple mating types in mushrooms

Having multiple mating types greatly improves the chances of meeting a compatible mating partner, particularly in an organism like the mushroom that has no sexual differentiation and no mechanism for signalling to a likely mate. Having several thousands of mating types, as some mushrooms do, is, however, remarkable - and even more remarkable is the fact that individuals only recognise that they have met a compatible mate after their cells have fused. How are such large numbers of mating types generated and what is the nature of the intracellular interaction that distinguishes self from non- self? Answers to these fascinating questions come from cloning some of the mating type genes of the ink cap mushroom Coprinus cinereus. A successful mating in Coprinus triggers a major switch in cell type, the conversion of a sterile mycelium with uninucleate cells (monokaryon) to a fertile mycelium with binucleate cells (dikaryon) which differentiates the characteristic fruit bodies. The mating type genes that regulate this developmental switch map to two multiallelic loci designated A and B and these must both carry different alleles for full mating compatibility. A and B independently regulate different steps in the developmental switch, making it possible to study just one component of the system and work in our laboratory has concentrated on understanding the structure and function of the A genes. It is estimated that some 160 different A mating types exist in nature, any two of which can together trigger the A-regulated part of sexual development. The first clue to how such large numbers are generated came from classical genetic analysis, which identified two functionally redundant A loci, (alpha) and beta. Functional redundancy is, indeed, the key to multiple A mating types and, as seen in Fig.1, molecular cloning has identified many more genes than was possible by recombination analysis.