Absidia, Ampelomyces, fusion parasitism, hyphal surface,
mucoralean fungi, nuclear fusion, Parasitella, trisporic acid,
The zygomycete Parasitella parasitica is a facultative fusion parasite of many but not all mucoralean fungi. In model experiments with one of the natural hosts, Absidia glauca, the propagation success of the host is reduced not more than approximately 40% at the level of sporangiospore formation, but growth of the parasite is increased considerably. Infection is inevitably accompanied by the formation of a limited cytoplasmic fusion between the parasite and its host. This process leads to frequent parasexual recombination events by transfer of genes from the parasite to the host. In this respect, the Parasitella biology offers one of very few experimental systems, where horizontal gene transfer in eukaryotes can be studied in the laboratory at molecular and biochemical levels. The infection process bears many similarities to the sexual system in zygomycetes. Especially primary recognition of the partners is mediated by the same type of diffusible and partly volatile compounds, the carotene-related derivatives of trisporic acid. This parasexual system is described here in comparison to sexual development in zygomycetes, and open questions are pointed out that should be addressed by the community.