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.

Role of Horizontal Gene Transfer in the Evolution of Fungi

“…Though intriguing, this research has left many questions unanswered. Mechanisms are unknown for the processes of DNA transfer, the selectivity of transfer, the basis for the replication, and instability of the transferred genes in the recipient (174). Working hypotheses favor a view in which foreign DNA may enter the nuclei in Absidia via a pathway analogous to transformation, after the nuclei in Parasitella disintegrate, and that the foreign DNA may be maintained unstably as extrachromosomal elements (89,175).…”

Trisporoids and carotenogenesis in Blakeslea trispora

“…In addition to interaction between the (+) and (-) strains of the same species, existence of a common sys tem of hormonal regulation in mucoraceous fungi also provides (a) passage of sexual reactions between the complementary (+) and (-) strains of different species (and even families) and (b) interaction between the host organism and a parasitic organism that is sexually complementary to it [3,4,6]. Sexual reactions are manifested in cessation of vegetative mycelium growth and in zygosporophore and gametangium formation; however, no mature zygosporophores are produced [41,53].…”

“…TSA and their precursors are produced during a sexual interaction and are signal molecules that ini tiate and control the sexual reactions between the (+) and (-) mycelia of heterothallic species, the (+) and (-) copulating branches of homothallic species, as well as the interaction between mycoparasites of muc oraceous fungi with the complementary strains of the host fungus [3][4][5][6].…”

Methods Used by Dr. R. K. Benjamin, and Other Mycologists, to Isolate Zygomycetes

“…Parasitella parasitica grows and sporulates well between 15uC and 30uC, and zygospores form at 20uC (Schipper 1978b). In nature, P. parasitica parasitizes only hosts of the opposite mating type, inducing a transfer of genetic information in the process (Kellner et al 1991;Wö stemeyer et al 1995). The galls of P. parasitica were unwittingly illustrated before the fungus was described (Thaxter 1895;Blakeslee 1904).…”