Zygomycetes & Chytrids,true fungi(with comments on systematics and nomenclature) Mycology (Bio 594, Special Topics) M. Marshall 2013 Shippensburg University (See last slide for credits)
Fungi versus fungi • “fungus” is used inclusively for a heterogenous group of organisms that have traditionally been studied by mycologists • “Fungi” refers to the organisms in the Kingdom Fungi, the true fungi, also called the “Eumycota” @
Reconstructing the early evolution of Fungi using a six-gene phylogeny. James et al. 2006. Nature 443: 818 @
Hierarchical Classification Kingdom Fungi Phylum Basidiomycota Class Basidiomycetes Order Agaricales Family Agaricaceae Genus Agaricus Species: Agaricus campestris L. @
Agaricus campestris L. • Agaricus is the genus • campestris is the specific epithet • The genus + species is the Latin binomial • L. stands for Linnaeus, the authority @
Agaricus bisporus (Lange) Imbach • Lange first described this fungus as Coprinus bisporus • Imbach later transferred the species to Agaricus @
Nomenclature • Nomenclature: the “allocation of scientific names to the units a systematist considers to merit formal recognition.” (Hawksworth et al., 1995. The Dictionary of the Fungi). • The nomenclature of fungi is governed by the International Code for Botanical Nomenclature, as adopted by the International Botanical Congress. • The rules for naming fungi were recently changed to simplify the process, eliminate the use of the pleiomorphic naming system (separate anamorph and teleomorph names), and allow for entries based on DNA sequences only. @
Typological Species Concept • "Species are as many as were created in the beginning by the Infinite." (Linnaeus, 1758) • Each species (was) represented by a type specimen, designated in the original description and deposited in a recognized collection (eg., herbarium) • The name is tied to the type specimen • The type specimen is not necessarily typical of the entire species! @
How are fungi named? • To determine the correct name for a taxon, certain steps must be followed, including: • Effectivepublication – only certain types of publication are considered “effective” • Validpublication – validity is assessed by how well the process adheres to a series of stringent regulations. • Description or diagnosis in Latin (no longer required) • Clear indication of rank • Designated type @
Fungal life cycles • The vegetative thallus predominates in the life cycle of a fungus • The thallus may be haploid (1n), dikaryotic (n+n) or diploid (2n) in different groups of fungi • Ploidy of thallus is determined by the relative timing of these events in the life cycle (the sequence in which they occur): • Plasmogamy (cell fusion) • Karyogamy (nuclear fusion) • Meiosis (reduction division) @
Zygomycetes mate to produce thick walled resistant zygospores which often have species-specific ornamentation
Pilobolus, (Mucorales) Pilobolus has evolved a way to shoot its spores on to grass away from the cow dung it grows on. Its "shotgun" is a stalk swollen with cell sap, bearing a black mass of spores on the top. Below the swollen tip is a light-sensitive area. The light sensing region causes the sporophoreto face toward the sun. As the fungus matures, water pressure builds in the stalk until the tip explodes, shooting the spores into the daylight. The spores fly away at 35 feet per second (10.8 m per second), at a height of six feet (2 m), and land as far away as 8 feet (2.5 m). Shooting the spores into the daylight gives them a better chance of landing on plants in a sunny place The cows that made the dung for the previous batch of Pilobolus will probably eat these spore covered plants and start the process all over again.
Characteristics of the Glomeromycota • obligate mutualistic symbiontson/in plant roots; aid in absorptiion. = Vessiculararbuscularmycorrhizae (VAM). About 80% of land plants are endomycorrhizal. • formation of arbuscules and sometimes vessicles inside plant root cells • large, multinucleate spores with layered walls • non-septatehyphae • Do not produce zygospore, no observable sexual cycle. • Placed in separate Phylum, as a sister group of Asco- & Basidiomycota. • Four (to 10) recognized genera: Glomus, Sclerocystis, AcaulosporaandGigasporaover 200 speciesknown. These will be covered in greater detail later
Chytrids • Placed in the Chytridiomycota, some authorities include the Blastocladiomycota hereas well, some (from the Tree of Life, below) place these in a separate phylum. • Morphologically simple, aquatic (fresh water & marine) or terrestrial in wet soil, over 700 described species, world-wide distribution. • Some are saprophytic (some are anaerobic!, theNeocallomastigalesin ruminants) or parasitic on plants and animals. Saprophytes can be “baited” by flooding soil and adding hard-to-digest substrates, cellulose, chitin, pollen grains, etc.
Chytrid types BK book
Chytrid morphology & biochemistry • Morphology simplistic; some unicellular with bulbous thallus with rhizoid filaments on one end, eucarpic with only bulbous sporangium producing spores, others holocarpic with whole thallus differentiating into spores. Epibiotic or endobiotic. • All produce asexual zoospores at some point in the life cycle, most with one rear flagellum, some multiflagellate. Sexual or asexual resting spores produced. • Some filamentous mycelial or with a network of fibrerousrhyzoids = rhyzomycelium. • All are biochemically fungi in regard to cell wall (chytin) construction, lysine production pathway, using glycogen for storage, similar rDNA sequences, etc. • Subclassified on basis of life cycle (sporicvs zygotic meiosis), morphology, zoospore morphology, etc. • Newer sources consider Blastocladiales, withaltertion of generations, and anaerobic ruminant inhabitants, the theNeocallomastigalesasdifferent phylla (= -mycota ending).
Allomyces, aBlastocladialeschytrid zygote germinates karyogamy, zygote encysts plasmogamy
Credits @ Designates slides wholly or partially stolen from various PowerPoint presentations created by Dr. Lori Carris for General Mycology 421/521, 2009, Plant Pathology, Dept. WSU.
Credits This presentation has been modified from one posted on the web by Dr. Lori Carris, Washigton State University Plant Pathology Dept. from her course: Plant Path 521, Mycology.