ARS | Publication request: PHYLOGENETIC RELATIONSHIPS AMONG PARASITIC ZYGOMYCOTA

Submitted to: Molecular Phylogenetics and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 20, 1999
Publication Date: N/A

Interpretive Summary: The phylum Zygomycota comprises all fungi that produce nonmotile spores within an enclosed spore case. Fungi within this phylum are responsible for many serious plant and animal diseases, including ones that are fatal in humans. In addition, this group includes agronomically and industrially important species used for food and the fermentation of a wide range of organic compounds. Efforts to develop a predictive, natural classification of these fungi has proven difficult because of their morphological simplicity. The purpose of this study was to investigate the origin and evolution of parasitic Zygomycota, focusing on groups that are obligate pathogens of animals and fungi. Molecular genetic analyses identified a novel group exclusively pathogenic on animals and fungi. A general conclusion from this study is that a molecular genetic data from slowly evolving protein molecules will be necessary to more fully elucidate the origin and genetic relationships of the fungi. Development of a natural classification of the fungi has enormous economic potential in that it should greatly increase our ability to predict, for example, the production of industrially important compounds by these agronomically and industrially-important fungi.

Technical Abstract: We sequenced the 18S rDNA gene from the rotifer parasite Zoophagus insidians and representatives of eight mycoparasitic or zooparasitic genera to investigate the origin and evolution parasitism within the Zygomycota. Phylogenetic analyses identified a novel monophyletic clade consisting of the Zoopagales, Kickxellales, Spiromyces, and Harpellales. Analyses also identified a monophyletic mycoparasitic-zooparasite Zoopagales clade in which Syncephalis, Thamnocephalis, and Rhopalomyces form a sister group to a Piptocephalis-Kuzuhaea clade. Result of the molecular phylogeny suggests that holdfasts, which attach members of the Harpellales to the gut of their insect hosts, are orthologous with haustoria of the Zoopagales. Although monophyly of the mycoparasitic Dimargaritales received strong bootstrap and decay clade support, phylogenetic relationships of this order could not be resolved because of the unusually high rate of base substitution within the 18S rDNA gene. Overall, the 18S gene tree topology is weak as reflected by low bootstrap support and decay indices for virtually all internal nodes uniting ordinal and superordinal taxa.