Transcript 4-zygomycetes - Shippensburg University

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)
The True fungi or Eumycota
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”
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Reconstructing the early evolution
of Fungi using a six-gene phylogeny.
James et al. 2006. Nature 443: 818
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Hierarchical Classification
Kingdom Fungi
Phylum Basidiomycota
Class Basidiomycetes
Order Agaricales
Family Agaricaceae
Genus Agaricus
Species:
Agaricus campestris L.
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Agaricus campestris L.
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Agaricus is the genus
campestris is the specific epithet
The genus + species is the Latin binomial
L. stands for Linnaeus, the authority
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Agaricus bisporus (Lange) Imbach
• Lange first described this fungus as Coprinus bisporus
• Imbach later transferred the species to Agaricus
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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.
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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!
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How are fungi named?
• To determine the correct name for a taxon, certain steps must
be followed, including:
– Effective publication – only certain types of publication are
considered “effective”
– Valid publication – 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
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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)
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Figure 31.3 Generalized life cycle of fungi (Layer 3)
R. Stolonifer life cycle
Rhizopus life cycle according to your text
Zygomycetes mate to produce thick walled resistant
zygospores which often have species-specific ornamentation
R. Stolonifer & Pilobolus crystallinus showing
suspensors and zygospore
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 lightsensitive area. The light sensing region causes
the sporophore to 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.
Glomeromycota
Characteristics of the Glomeromycota
• obligate mutualistic symbionts on/in plant roots; aid in absorptiion. =
Vessicular arbuscular mycorrhizae (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-septate hyphae
• 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, Acaulospora and
Gigaspora over 200 species known.
These will be covered in greater detail later
SPACER
Chytrids coming soon
Figure 31.5 Chytridiomycota (chytrids)
Chytrids
• Placed in the Chytridiomycota, some authorities include the Blasto
cladiomycota here as 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!, the Neocallomastigales in
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
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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 fibrerous rhyzoids =
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 (sporic vs zygotic meiosis), morphology,
zoospore morphology, etc.
Newer sources consider Blastocladiales, with altertion of generations, and
anaerobic ruminant inhabitants, the the Neocallomastigales as different
phylla (= -mycota ending).
Rhizophidium spp
Allomyces, a Blastocladiales chytrid
zygote germinates
karyogamy, zygote encysts
plasmogamy
Zoospore differentiation in Blastocladiella.
Synchytrium endobioticum
Potato Black Wart incited by S. endobioticum
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.