Basidiomycota (/bəˌsɪdi.oʊmaɪˈkoʊtə/) is one of two large
divisions that, together with the Ascomycota, constitute the
Dikarya (often referred to as the "higher fungi") within
the kingdom Fungi.
More specifically the
Basidiomycota include these groups: mushrooms,
puffballs, stinkhorns, bracket fungi, other polypores, jelly fungi,
boletes, chanterelles, earth stars, smuts, bunts, rusts, mirror
yeasts, and the human pathogenic yeast Cryptococcus.
Basidiomycota are filamentous fungi composed of hyphae (except for
basidiomycota-yeast; refer yeast for more information) and reproduce
sexually via the formation of specialized club-shaped end cells called
basidia that normally bear external meiospores (usually four). These
specialized spores are called basidiospores. However, some
Basidiomycota reproduce asexually in addition or exclusively.
Basidiomycota that reproduce asexually (discussed below) can be
recognized as members of this division by gross similarity to others,
by the formation of a distinctive anatomical feature (the clamp
connection - see below), cell wall components, and definitively by
phylogenetic molecular analysis of
DNA sequence data.
2 Typical life-cycle
3 Variations in lifecycles
4 Genera incertae sedis
5 See also
7 External links
The most recent classification adopted by a coalition of 67
mycologists recognizes three subphyla (Pucciniomycotina,
Ustilaginomycotina, Agaricomycotina) and two other class level taxa
(Wallemiomycetes, Entorrhizomycetes) outside of these, among the
Basidiomycota. As now classified, the subphyla join and also cut
across various obsolete taxonomic groups (see below) previously
commonly used to describe Basidiomycota. According to a 2008 estimate,
Basidiomycota comprise three subphyla (including six unassigned
classes) 16 classes, 52 orders, 177 families, 1,589 genera, and 31,515
Basidiomycota were divided into two classes, now
Homobasidiomycetes (alternatively called holobasidiomycetes),
including true mushrooms
Heterobasidiomycetes, including the jelly, rust and smut fungi
Previously the entire
Basidiomycota were called Basidiomycetes, an
invalid class level name coined in 1959 as a counterpart to the
Ascomycetes, when neither of these taxa were recognized as divisions.
The terms basidiomycetes and ascomycetes are frequently used loosely
to refer to
Basidiomycota and Ascomycota. They are often abbreviated
to "basidios" and "ascos" as mycological slang.
Agaricomycotina include what had previously been called the
Hymenomycetes (an obsolete morphological based class of Basidiomycota
that formed hymenial layers on their fruitbodies), the Gasteromycetes
(another obsolete class that included species mostly lacking hymenia
and mostly forming spores in enclosed fruitbodies), as well as most of
the jelly fungi. The three classes in the
Agaricomycotina are the
Agaricomycetes, the Dacrymycetes, and the Tremellomycetes.
Wallemiomycetes is not yet placed in a subdivision, but
recent genomic evidence suggests that it is a sister group of
Pucciniomycotina include the rust fungi, the insect
parasitic/symbiotic genus Septobasidium, a former group of smut fungi
(in the Microbotryomycetes, which includes mirror yeasts), and a
mixture of odd, infrequently seen, or seldom recognized fungi, often
parasitic on plants. The eight classes in the
Agaricostilbomycetes, Atractiellomycetes, Classiculomycetes,
Cryptomycocolacomycetes, Cystobasidiomycetes, Microbotryomycetes,
Mixiomycetes, and Pucciniomycetes.
Ustilaginomycotina are most (but not all) of the former smut fungi
and the Exobasidiales. The classes of the
Ustilaginomycotina are the
Exobasidiomycetes, the Entorrhizomycetes, and the
Sexual reproduction cycle of basidiomycetes
Unlike animals and plants which have readily recognizable male and
Basidiomycota (except for the Rust (Pucciniales))
tend to have mutually indistinguishable, compatible haploids which are
usually mycelia being composed of filamentous hyphae. Typically
Basidiomycota mycelia fuse via plasmogamy and then the
compatible nuclei migrate into each other's mycelia and pair up with
the resident nuclei.
Karyogamy is delayed, so that the compatible
nuclei remain in pairs, called a dikaryon. The hyphae are then said to
be dikaryotic. Conversely, the haploid mycelia are called monokaryons.
Often, the dikaryotic mycelium is more vigorous than the individual
monokaryotic mycelia, and proceeds to take over the substrate in which
they are growing. The dikaryons can be long-lived, lasting years,
decades, or centuries. The monokaryons are neither male nor female.
They have either a bipolar (unifactorial) or a tetrapolar
(bifactorial) mating system. This results in the fact that following
meiosis, the resulting haploid basidiospores and resultant
monokaryons, have nuclei that are compatible with 50% (if bipolar) or
25% (if tetrapolar) of their sister basidiospores (and their resultant
monokaryons) because the mating genes must differ for them to be
compatible. However, there are sometimes more than two possible
alleles for a given locus, and in such species, depending on the
specifics, over 90% of monokaryons could compatible with each other.
The maintenance of the dikaryotic status in dikaryons in many
Basidiomycota is facilitated by the formation of clamp connections
that physically appear to help coordinate and re-establish pairs of
compatible nuclei following synchronous mitotic nuclear divisions.
Variations are frequent and multiple. In a typical Basidiomycota
lifecycle the long lasting dikaryons periodically (seasonally or
occasionally) produce basidia, the specialized usually club-shaped end
cells, in which a pair of compatible nuclei fuse (karyogamy) to form a
Meiosis follows shortly with the production of 4 haploid
nuclei that migrate into 4 external, usually apical basidiospores.
Variations occur, however. Typically the basidiospores are ballistic,
hence they are sometimes also called ballistospores. In most species,
the basidiospores disperse and each can start a new haploid mycelium,
continuing the lifecycle.
Basidia are microscopic but they are often
produced on or in multicelled large fructifications called
basidiocarps or basidiomes, or fruitbodies), variously called
mushrooms, puffballs, etc. Ballistic basidiospores are formed on
sterigmata which are tapered spine-like projections on basidia, and
are typically curved, like the horns of a bull. In some Basidiomycota
the spores are not ballistic, and the sterigmata may be straight,
reduced to stubbs, or absent. The basidiospores of these
non-ballistosporic basidia may either bud off, or be released via
dissolution or disintegration of the basidia.
Scheme of a typical basidiocarp, the dipoid reproductive structure of
a basidiomycete, showing fruiting body, hymenium and basidia.
In summary, meiosis takes place in a diploid basidium. Each one of the
four haploid nuclei migrates into its own basidiospore. The
basidiospores are ballistically discharged and start new haploid
mycelia called monokaryons. There are no males or females, rather
there are compatible thalli with multiple compatibility factors.
Plasmogamy between compatible individuals leads to delayed karyogamy
leading to establishment of a dikaryon. The dikaryon is long lasting
but ultimately gives rise to either fruitbodies with basidia or
directly to basidia without fruitbodies. The paired dikaryon in the
basidium fuse (i.e. karyogamy takes place). The diploid basidium
begins the cycle again.
Coprinopsis cinerea is a multicellular basidiomycete mushroom. It is
particularly suited to the study of meiosis because meiosis progresses
synchronously in about 10 million cells within the mushroom cap, and
the meiotic prophase stage is prolonged. Burns et al. studied the
expression of genes involved in the 15-hour meiotic process, and found
that the pattern of gene expression of C. cinerea was similar to two
other fungal species, the yeasts
Saccharomyces cerevisiae and
Schizosaccharomyces pombe. These similarities in the patterns of
expression led to the conclusion that the core expression program of
meiosis has been conserved in these fungi for over half a billion
years of evolution since these species diverged.
Cryptococcus neoformans and
Ustilago maydis are examples of pathogenic
basidiomycota. Such pathogens must be able to overcome the oxidative
defenses of their respective hosts in order to produce a successful
infection. The ability to undergo meiosis may provide a survival
benefit for these fungi by promoting successful infection. A
characteristic central feature of meiosis is recombination between
homologous chromosomes. This process is associated with repair of DNA
damages, particularly double-strand breaks. The ability of C.
neoformans and U. maydis to undergo meiosis may contribute to their
virulence by removing the oxidative DNA damages caused by their
host’s release of reactive oxygen species.
Variations in lifecycles
Many variations occur. Some are self-compatible and spontaneously form
dikaryons without a separate compatible thallus being involved. These
fungi are said to be homothallic, versus the normal heterothallic
species with mating types. Others are secondarily homothallic, in that
two compatible nuclei following meiosis migrate into each
basidiospore, which is then dispersed as a pre-existing dikaryon.
Often such species form only two spores per basidium, but that too
varies. Following meiosis, mitotic divisions can occur in the
basidium. Multiple numbers of basidiospores can result, including odd
numbers via degeneration of nuclei, or pairing up of nuclei, or lack
of migration of nuclei. For example, the chanterelle genus Craterellus
often has six-spored basidia, while some corticioid
can have two-, four-, six-, or eight-spored basidia, and the
cultivated button mushroom, Agaricus bisporus. can have one-, two-,
three- or four-spored basidia under some circumstances. Occasionally,
monokaryons of some taxa can form morphologically fully formed
basidiomes and anatomically correct basidia and ballistic
basidiospores in the absence of dikaryon formation, diploid nuclei,
and meiosis. A rare few number of taxa have extended diploid
lifecycles, but can be common species. Examples exist in the mushroom
Armillaria and Xerula, both in the Physalacriaceae.
Occasionally, basidiospores are not formed and parts of the "basidia"
act as the dispersal agents, e.g. the peculiar mycoparasitic jelly
fungus, Tetragoniomyces or the entire "basidium" acts as a "spore",
e.g. in some false puffballs (Scleroderma). In the human pathogenic
genus Cryptococcus, four nuclei following meiosis remain in the
basidium, but continually divide mitotically, each nucleus migrating
into synchronously forming nonballistic basidiospores that are then
pushed upwards by another set forming below them, resulting in four
parallel chains of dry "basidiospores".
Other variations occur, some as standard lifecycles (that themselves
have variations within variations) within specific orders.
Rusts (Pucciniales, previously known as Uredinales) at their greatest
complexity, produce five different types of spores on two different
host plants in two unrelated host families. Such rusts are
heteroecious (requiring two hosts) and macrocyclic (producing all five
spores types). Wheat stem rust is an example. By convention, the
stages and spore states are numbered by Roman numerals. Typically,
basidiospores infect host one, also known as the alternate or sexual
host, the mycelium forms pycnidia, which are miniature, flask-shaped,
hollow, submicroscopic bodies embedded in host tissue (such as a
leaf). This stage, numbered "0", produces single-celled spores that
ooze out in a sweet liquid and that act as nonmotile spermatia, and
also protruding receptive hyphae. Insects and probably other vectors
such as rain carry the spermatia from spermagonium to spermagonium,
cross inoculating the mating types. Neither thallus is male or female.
Once crossed, the dikaryons are established and a second spore stage
is formed, numbered "I" and called aecia, which form dikaryotic
aeciospores in dry chains in inverted cup-shaped bodies embedded in
host tissue. These aeciospores then infect the second host, known as
the primary or asexual host (in macrocyclic rusts). On the primary
host a repeating spore stage is formed, numbered "II", the
urediospores in dry pustules called uredinia. Urediospores are
dikaryotic and can infect the same host that produced them. They
repeatedly infect this host over the growing season. At the end of the
season, a fourth spore type, the teliospore, is formed. It is
thicker-walled and serves to overwinter or to survive other harsh
conditions. It does not continue the infection process, rather it
remains dormant for a period and then germinates to form basidia
(stage "IV"), sometimes called a promycelium. In the Pucciniales, the
basidia are cylindrical and become 3-septate after meiosis, with each
of the 4 cells bearing one basidiospore each. The basidiospores
disperse and start the infection process on host 1 again. Autoecious
rusts complete their life-cycles on one host instead of two, and
microcyclic rusts cut out one or more stages.
The characteristic part of the life-cycle of smuts is the
thick-walled, often darkly pigmented, ornate, teliospore that serves
to survive harsh conditions such as overwintering and also serves to
help disperse the fungus as dry diaspores. The teliospores are
initially dikaryotic but become diploid via karyogamy.
place at the time of germination. A promycelium is formed that
consists of a short hypha (equated to a basidium). In some smuts such
Ustilago maydis the nuclei migrate into the promycelium that
becomes septate (i.e., divided into cellular compartments separated by
cell walls called septa), and haploid yeast-like conidia/basidiospores
sometimes called sporidia, bud off laterally from each cell. In
various smuts, the yeast phase may proliferate, or they may fuse, or
they may infect plant tissue and become hyphal. In other smuts, such
as Tilletia caries, the elongated haploid basidiospores form apically,
often in compatible pairs that fuse centrally resulting in "H"-shaped
diaspores which are by then dikaryotic. Dikaryotic conidia may then
form. Eventually the host is infected by infectious hyphae.
Teliospores form in host tissue. Many variations on these general
Smuts with both a yeast phase and an infectious hyphal state are
examples of dimorphic Basidiomycota. In plant parasitic taxa, the
saprotrophic phase is normally the yeast while the infectious stage is
hyphal. However, there are examples of animal and human parasites
where the species are dimorphic but it is the yeast-like state that is
infectious. The genus
Filobasidiella forms basidia on hyphae but the
main infectious stage is more commonly known by the anamorphic yeast
name Cryptococcus, e.g.
Cryptococcus neoformans and Cryptococcus
Basidiomycota with yeast stages and the pleiomorphic
rusts are examples of fungi with anamorphs, which are the asexual
Basidiomycota are only known as anamorphs. Many are
yeasts, collectively called basidiomycetous yeasts to differentiate
them from ascomycetous yeasts in the Ascomycota. Aside from yeast
anamorphs, and uredinia, aecia and pycnidia, some
other distinctive anamorphs as parts of their life-cycles. Examples
are Collybia tuberosa with its apple-seed-shaped and coloured
Dendrocollybia racemosa  with its sclerotium and its
Tilachlidiopsis racemosa conidia,
Armillaria with their
Hohenbuehelia  with their
infectious, state and the coffee leaf parasite, Mycena
citricolor and its
Decapitatus flavidus propagules called gemmae.
Genera incertae sedis
There are several genera classified in the
Basidiomycota that are i)
poorly known, ii) have not been subjected to DNA analysis, or iii) if
analysed phylogenetically do not group with as yet named or identified
families, and have not been assigned to a specific family (i.e., they
are incertae sedis with respect to familial placement). These include:
Anastomyces W.P.Wu, B.Sutton & Gange (1997)
Anguillomyces Marvanová & Bärl. (2000)
Anthoseptobasidium Rick (1943)
Arcispora Marvanová & Bärl. (1998)
Arrasia Bernicchia, Gorjón & Nakasone (2011)
Brevicellopsis Hjortstam & Ryvarden (2008)
Celatogloea P.Roberts (2005)
Cleistocybe Ammirati, A.D.Parker & Matheny (2007)
Cystogloea P. Roberts (2006)
Dacryomycetopsis Rick (1958)
Eriocybe Vellinga (2011)
Hallenbergia Dhingra & Priyanka (2011)
Hymenoporus Tkalčec, Mešić & Chun Y.Deng (2015)
Kryptastrina Oberw. (1990)
Microstella K.Ando & Tubaki (1984)
Neotyphula Wakef. (1934)
Nodulospora Marvanová & Bärl. (2000)
Paraphelaria Corner (1966)
Punctulariopsis Ghob.-Nejh. (2010)
Radulodontia Hjortstam & Ryvarden (2008)
Restilago Vánky (2008)
Sinofavus W.Y.Zhuang (2008)
Zanchia Rick (1958)
Zygodesmus Corda (1837)
Zygogloea P.Roberts (1994)
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