Relationships between sexual processes and parasitic interactions in the host–pathogen systemAbsidia glauca–Parasitella parasitica

Abstract

Parasitella parasitica is a facultative parasite of many Mucorales including Absidia glauca. The infection process includes the formation of a plasmatic continuum between host and parasite, which allows the invasion of the host by nuclei of the parasite. This process gives rise to interspecies recombinants. Auxotrophic A. glauca mutants are complemented by the transfer of genes from the parasite to the host. At the molecular level, we could show that plasmid-coded genes are also transferred. The successful formation of infection structures is mating-type dependent. Parasitella parasitica exclusively infects hosts belonging to the complementary mating type. The formation of infection structures is correlated with the ability to synthesise the sex pheromone trisporic acid, which is produced in mixed cultures by compatible combinations between host and parasite. Normally, trisporic acid is formed by a cooperative biosynthesis involving both mating types. Trisporic acid seems to be involved also in mediating the recognition between P. parasitica and A. glauca. To test the hypothesis of direct hormonal correlations between sex and parasitism, we have isolated one of the key enzymes for trisporic acid synthesis, dihydromethyltrisporic acid dehydrogenase, sequenced the N-termini of some proteolytic cleavage products, and have started to isolate the corresponding gene. Key words: mycoparasitism, zygomycetes, trisporic acid, Absidia glauca, Parasitella parasitica, Mucor.