''Syzygites'' is a monotypic genus in Zygomycota. The sole described species is ''Syzygites megalocarpus'', which was the first fungus for which sex was reported and the main homothallic representative in the research that allowed for the classification of fungi as homothallic or heterothallic. It is also the fungus from which the term " zygospore" was coined.

Morphology

Syzygites megalocarpus 400x dichotomous sporangiophores

''Syzygites megalocarpus'' produces

phototropic Phototropism is the growth of an organism in response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light contain a hor ...

, repeatedly dichotomously branched sporangiophores that terminate in globose, apophysate sporangia. Sporangiospores have a spinose wall, which is rare in Mucorales. Zygospores are pigmented, ornamented, and produced on equally sized suspensors. Due to the presence of

carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, and Fungus, fungi. Carotenoids give the characteristic color to pumpki ...

s, the myceliuem can appear yellowish, though mature sporangia darken giving it a brownish appearance.

Ecology

''S. megalocarpus'' is a

necrotroph A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...

ic parasite of mushrooms in temperate regions, though there are reports of it from

ascomycetes Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defi ...

. It can parasitize at least 98 different species and is itself parasitized by ''Piptocephalis virginiana''. ''Syzygites megalocarpus'' is likely a faculative parasite as it can be grown on a variety of media, including bread, in the laboratory. Development of asexual sporangia and zygospores are highly dependent upon environmental conditions. In the laboratory, growth occurs between 5-30 degrees Celsius. Alternating light and dark increases the formation of sporangiophores and continual darkness increases the production of zygospores. Lower temperatures favor zygospore formation and higher temperatures favor sporangiophore production. Media with high quality carbon sources favors formation of zygospores, while media with high nitrogen favors formation of sporangiophores. High humidity increases zygospore formation and low humidity increases sporangiophore formation.

Sexuality

''Syzygites megalocarpus'' is a homothallic fungus, which means each individual contains both mating loci and can therefore self-fertilize to form zygospores. The genes identified in the Mucoromyoctina fungi Phycomyces and Rhizopus are named ''sexM'' and ''sexP'' for the minus (-) and plus (+) mating types which these gene define. The genes are members of the HMG

high-mobility group High-Mobility Group or HMG is a group of chromosomal proteins that are involved in the regulation of DNA-dependent processes such as transcription, replication, recombination, and DNA repair. Families The HMG proteins are subdivided into 3 super ...

gene family. As in other members of Mucorales, these genes are flanked by an RNA helicase and glutathione oxidoreductase.

Taxonomy

Ehrenberg described ''Syzygites megalocarpus'' in 1818 based on its zygospores and provided illustrations for the fungus in 1829. In 1824, Link described ''Sporodinia grandis'' based on the asexual state of ''Syzygites megalocarpus''. In 1832, Fries considered ''S. megalocarpus'' and ''S. grandis'' to be the same species, though this was not observed until 1855 by Tulasne. Hesseltine summarized the taxonomy of the genus in his 1957 monograph and synonymized 14 species with ''Syzygites megalocarpus''. In a molecular phylogeny, ''Syzygites megalocarpus'' is placed sister to ''Sporodinella umbellata'', albeit in a clade with '' Rhizopus''.

References

{{Taxonbar, from=Q10687814 Zygomycota Fungus genera Taxa named by Christian Gottfried Ehrenberg