Basidiomycota is one of two large
phylaIn biology, a phylum ["Phylum" is adopted from the Greek phylai, the clan-based voting groups in Greek city-states.] is a taxonomic rank below Kingdom and above Class...
that, together with the
AscomycotaThe Ascomycota are a Division/Phylum of the kingdom Fungi, and subkingdom Dikarya. Its members are commonly known as the Sac Fungi. They are the largest phylum of Fungi, with over 64,000 species...
, comprise the subkingdom
DikaryaDikarya is a subkingdom of Fungi that includes the phyla Ascomycota and Basidiomycota, both of which in general produce dikaryons, may be filamentous or unicellular, but are always without flagella. The Dikarya are most of the so called "Higher Fungi", but also include many anamorphic species that...
(often referred to as the
"Higher Fungi") within the Kingdom Fungi. More specifically the Basidiomycota include
mushroomA mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus, hence the word mushroom is most often applied to those fungi that have...
s, puffballs, stinkhorns, bracket fungi, other polypores,
jelly fungiThe class Heterobasidiomycetes or jelly fungi is a paraphyletic group of several fungal orders: Tremellales, Auriculariales, Dacrymycetales. These fungi are so named because their foliose to irregularly branched fruiting body is, or appears to be, the consistency of jelly. Actually, many are...
, boletes,
chanterellesCantharellus is a genus with many popular edible mushrooms. It is a mycorrhizal edible fungus, meaning it forms symbiotic associations with plants, making it very challenging to cultivate. Caution must be used when identifying chanterelles for consumption; lookalikes, such as the Jack-O-Lantern ,...
,
earth starsThe earthstars are the family Geastraceae of gasterocarpic basidiomycetes . It includes the genera Geastrum and Myriostoma...
,
smutsThe smuts are fungi, mostly Ustilaginomycetes , that cause plant disease.Smuts affect grasses, notably including cereal crops such as maize...
,
buntsCommon bunt, also known as stinking smut and covered smut is a disease of both spring and winter wheats. It is caused by two very closely related fungi, Tilletia tritici and T. laevis Common bunt, also known as stinking smut and covered smut is a disease of both spring and winter wheats. It is...
,
rustsRusts are fungi of the order Uredinales. Many of these species are plant parasites. Some are superficially similar to the smuts, although their relation to each other is not clear. The taxonomy of Urediniomycota, as a whole, is in a state of flux....
, mirror yeasts, and the human pathogenic yeast,
CryptococcusCryptococcus is a genus of fungus. It grows in culture as a yeast. The perfect form or teleomorph is called Filobasidiella, but the imperfect form or anamorph is called Cryptococcus...
. Basically, Basidiomycota are filamentous fungi composed of hyphae (except for those forming yeasts), and reproducing sexually via the formation of specialized club-shaped end
cellThe cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of an organism that is classified as living, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos...
s called basidia that normally bear external
meiosporeIn biology, meiosis is a process of reductional division in which the number of chromosomes per cell is cut in half. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores. As with mitosis, before meiosis begins, the DNA in the original...
s (usually four). These specialized
sporeIn biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions...
s are called
basidiosporeA basidiospore is a reproductive spore produced by Basidiomycete fungi. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidia...
s. However, some Basidiomycota reproduce asexually, and may or may not also reproduce sexually. Asexually reproducing Basidiomycota (discussed below) can be recognized as members of this phylum by gross similarity to others, by the formation of a distinctive anatomical feature (the
clamp connectionA type of connection found within a single hyphal strand of a Basidiomycete fungus. It ensures that two adjacent hyphal cells each have 2 different nuclei from mating with hyphae of another sexual type. It is used in the "nuclear shuffle" similar to that found in croziers during sexual...
- see below),
cell wallA cell wall is a tough, flexible and sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to act as a...
components, and definitively by phylogenetic molecular analysis of
DNA sequenceA DNA sequence or genetic sequence is a succession of letters representing the primary structure of a real or hypothetical DNA molecule or strand, with the capacity to carry information as described by the central dogma of molecular biology....
data.
Classification
The most recent classification adopted by a coalition of 67 mycologists recognizes 3 subphyla (
PucciniomycotinaFor more information about the subphylum Pucciniomycotina, select one of the higher ranking taxa from the taxobox.-References:* M.C. Aime et al.: An overview of the higher level classification of Pucciniomycotina based on combined analyses of nuclear large and small subunit rDNA sequences....
,
UstilaginomycotinaUstilaginomycotina refers to a subphylum within the phylum Basidiomycota of the kingdom Fungi, consisting of the classes Ustilaginomycetes, Exobasidiomycetes and the order Malassezia.-External links:*...
,
AgaricomycotinaThe subphylum Agaricomycotina, also known as the hymenomycetes, is one of three taxa of the fungal division Basidiomycota . The Agaricomycotina contain some 20,000 species, and about 98% of these are in the class Agaricomycetes: most of the fungi known as mushrooms, including the bracket fungi and...
) and 2 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 various Basidiomycota.
The Basidiomycota had traditionally been divided into 2 obsolete classes, the Homobasidiomycetes (including true mushrooms); and the Heterobasidiomycetes (the Jelly,
RustRusts are fungi of the order Uredinales. Many of these species are plant parasites. Some are superficially similar to the smuts, although their relation to each other is not clear. The taxonomy of Urediniomycota, as a whole, is in a state of flux....
and
SmutThe smuts are fungi, mostly Ustilaginomycetes , that cause plant disease.Smuts affect grasses, notably including cereal crops such as maize...
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 phyla. 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.
The
AgaricomycotinaThe subphylum Agaricomycotina, also known as the hymenomycetes, is one of three taxa of the fungal division Basidiomycota . The Agaricomycotina contain some 20,000 species, and about 98% of these are in the class Agaricomycetes: most of the fungi known as mushrooms, including the bracket fungi and...
(see details on that page) includes what had previously been called the Hymenomycetes (an obsolete morphological based class of Basidiomycota that formed hymenial layers on their fruitbodies), the
GasteromycetesThe Gasteromycetes fungus is a subgroup of the class Basidiomycetes . The name literally means "stomach fungus," because the fungi produce their spores inside the fruiting body. Although the members of the group share the same name, that does not necessarily signify an evolutionary relationship...
(another obsolete class that included species mostly lacking hymenia and mostly forming spores in enclosed fruitbodies), as well as most of the
jelly fungiThe class Heterobasidiomycetes or jelly fungi is a paraphyletic group of several fungal orders: Tremellales, Auriculariales, Dacrymycetales. These fungi are so named because their foliose to irregularly branched fruiting body is, or appears to be, the consistency of jelly. Actually, many are...
.
The
UstilaginomycotinaUstilaginomycotina refers to a subphylum within the phylum Basidiomycota of the kingdom Fungi, consisting of the classes Ustilaginomycetes, Exobasidiomycetes and the order Malassezia.-External links:*...
are most (but not all) of the former smut fungi and along with the
ExobasidialesThe Exobasidiales are an order of fungi in the class Exobasidiomycetes. The order consists of four families as well as one genus, Cladosterigma, not assigned to any family....
.
The
PucciniomycotinaFor more information about the subphylum Pucciniomycotina, select one of the higher ranking taxa from the taxobox.-References:* M.C. Aime et al.: An overview of the higher level classification of Pucciniomycotina based on combined analyses of nuclear large and small subunit rDNA sequences....
includes 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.
Two classes, Wallemiomycetes and Entorrhizomycetes cannot at present be placed in a subphylum.
Typical life-cycle
Unlike higher animals and plants which have readily recognizable male and female counterparts, Basidiomycota (except for the
RustRusts are fungi of the order Uredinales. Many of these species are plant parasites. Some are superficially similar to the smuts, although their relation to each other is not clear. The taxonomy of Urediniomycota, as a whole, is in a state of flux....
(Pucciniales)) tend to have mutually indistinguishable, compatible haploids which are usually mycelia being composed of filamentous hyphae. Typically haploid Basidiomycota mycelia fuse via
plasmogamyPlasmogamy is a stage in the sexual reproduction of fungi. In this stage, the cytoplasm of two parent mycelia fuse together without the fusion of nuclei, as occurs in higher terrestrial fungi. After plasmogamy occurs, the secondary mycelium forms. The secondary mycelium consists of dikaryotic...
and then the compatible nuclei migrate into each other's mycelia and pair up with the resident nuclei.
KaryogamyKaryogamy is the fusion of pronuclei of two cells, as part of syngamy. It is one of the two major modes of reproduction in fungi. It is also the fusion of the pronuclei of two cells, as occurs in fertilization or true conjugation....
is delayed, so that the compatible nuclei remain in pairs, called a
dikaryonDikaryon is from Greek, di meaning 2 and karyon meaning nut, referring to the cell nucleus.The dikaryon is a nuclear feature which is unique to some fungi, in which after plasmogamy the two compatible nuclei of two cells pair off and cohabit without karyogamy within the cells of the hyphae,...
. 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
meiosisIn biology, meiosis is a process of reductional division in which the number of chromosomes per cell is cut in half. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores. As with mitosis, before meiosis begins, the DNA in the original...
, 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 many variations of these genes in the population, and therefore, over 90% of monokaryons are compatible with each other. It is as if there were multiple sexes.
The maintenance of the dikaryotic status in dikaryons in many Basidiomycota is facilitated by the formation of
clamp connectionA type of connection found within a single hyphal strand of a Basidiomycete fungus. It ensures that two adjacent hyphal cells each have 2 different nuclei from mating with hyphae of another sexual type. It is used in the "nuclear shuffle" similar to that found in croziers during sexual...
s 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 (
karyogamyKaryogamy is the fusion of pronuclei of two cells, as part of syngamy. It is one of the two major modes of reproduction in fungi. It is also the fusion of the pronuclei of two cells, as occurs in fertilization or true conjugation....
) to form a diploid cell.
MeiosisIn biology, meiosis is a process of reductional division in which the number of chromosomes per cell is cut in half. In animals, meiosis always results in the formation of gametes, while in other organisms it can give rise to spores. As with mitosis, before meiosis begins, the DNA in the original...
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
ballistosporeA spore that is shot off. In fungi most types of basidiospores, formed on basidia are discharged into the air from the tips of sterigmata. These actively discharged spores are a type of ballistospore....
s. 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.
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.
Variations in life-cycles
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
CraterellusCraterellus is a genus of generally edible fungi similar to the closely related chanterelles, with some species recently reassigned to this genus...
often has 6-spored basidia, while some corticioid
Sistotrema species can have 2-, 4-, 6-, or 8-spored basidia, and the cultivated button mushroom,
Agaricus bisporus. can have 1-, 2-, 3- or 4-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 life-cycles, but can be common species. Examples exist in the mushroom genera
Armillaria and
XerulaXerula is a genus of gilled mushrooms in the Physalacriaceae family.-Species:*Xerula americana*Xerula amygdaliformis*Xerula asprata*Xerula aureocystidiata*Xerula australis*Xerula caussei*Xerula chiangmaiae...
, both in the
PhysalacriaceaePhysalacriaceae is a family of fungi in the order Agaricales. Taxa have a widespread distribution, but most species are found in the tropics, particularly in South-East Asia and Australasia. Molecular studies suggested that Physalacria, formerly the sole genus in this family, is related to the...
. 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 (
SclerodermaScleroderma is a genus of fungi, commonly known as earth balls, now known to belong to the Boletales order, in suborder Sclerodermatineae.. The best known species are S. citrinum and S. verrucosum...
). In the human pathogenic genus
Filobasidiella 4 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 4 parallel chains of dry "basidiospores".
Other variations occur, some as standard life-cycles (that themselves have variations within variations) within specific orders.
Rusts
RustsRusts are fungi of the order Uredinales. Many of these species are plant parasites. Some are superficially similar to the smuts, although their relation to each other is not clear. The taxonomy of Urediniomycota, as a whole, is in a state of flux....
(Pucciniales, previously known as Uredinales) at their greatest complexity produce five different types of spores on two different hosts in two unrelated host families. Such rusts are heteroecious (requiring 2 hosts) and macrocyclic (producing all 5 spores types). Wheat
stem rustThe stem, black or cereal rusts are caused by the fungus Puccinia graminis and are a significant disease affecting cereal crops. An epidemic of stem rust on wheat caused by race Ug99 is currently spreading across Africa, Asia and most recently into Middle East and is causing major concern due to...
is an example. By convention the stages and spore states are numbered by
Roman numeralsRoman numerals are a numeral system of ancient Rome based on letters of the alphabet, which are combined to signify the sum of their values. The first ten Roman numerals are:...
. Typically, basidiospores infect host one, the mycelium forms pycnidia, called spermagonia, which are miniature, flask-shaped, hollow, submicroscopic bodies embedded in host tissue (such as a leaf). This stage, numbered "0", produces single-celled, minute spores that ooze out in a sweet liquid and that act as nonmotile spermatia, and also protruding receptive hyphae.
InsectInsects are arthropods, having a hard exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae. They are the most diverse group of animals on the planet and include more than a million species that are already described. Insects represent more than half of all...
s and probably other vectors such as rain carry the spermatia from spermagonia to spermagonia, 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 genus and cannot infect the host on which they are formed (in macrocyclic rusts). On the second 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
teliosporeTeliospore is the thick-walled resting spore of some fungi , from which the basidium arises.-Morphology:Teliospores are usually dark-coloured, and consist of two dikaryote cells...
, 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-
septateIn anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.- In human anatomy :* Interatrial septum, the wall of tissue that separates the left and right atria of the heart...
after meiosis, with each of the 4 cells bearing one basidiospore each. The basidospores 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.
Smuts
The characteristic part of the life-cycle of
smutsThe smuts are fungi, mostly Ustilaginomycetes , that cause plant disease.Smuts affect grasses, notably including cereal crops such as maize...
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
diasporesIn biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions...
. The teliospores are initially dikaryotic but become diploid via karyogamy. Meiosis takes place at the time of germination. A promycelim is formed that consists to a short hypha (equated to a basidium). In some smuts such as
Ustilago maydis the nuclei migrate into the promycelium that becomes septate, 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 cariesTilletia tritici is the causal agent of common bunt of wheat.The tilletia was named after French agronomist Mathieu Tillet .-Use as a biological weapon:...
, 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 themes occur.
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
CryptococcusCryptococcus is a genus of fungus. It grows in culture as a yeast. The perfect form or teleomorph is called Filobasidiella, but the imperfect form or anamorph is called Cryptococcus...
, e.g.
Cryptococcus neoformansCryptococcus neoformans is an encapsulated yeast-like fungus that can live in both plants and animals.This species, also known by its teleomorph name, Filobasidiella neoformans, belongs to the broad class of organisms called "club fungi" or Division Basidiomycota, which is one the five major types...
and
Cryptococcus gattiiCryptococcus gattii, also known as Cryptococcus neoformans var gattii, is an encapsulated yeast-like fungus found primarily in tropical and subtropical climates. It causes the human diseases of pulmonary cryptococcosis , basal meningitis, and cerebral cryptococcomas...
.
The dimorphic Basidiomycota with yeast stages and the pleiomorphic rusts are examples of fungi with anamorphs, which are the asexual stages. Some Basidiomycota are only known as anamorphs. Many are yeasts, collectively called basidiomycetous yeasts to differentiate them from ascomycetous yeasts in the
AscomycotaThe Ascomycota are a Division/Phylum of the kingdom Fungi, and subkingdom Dikarya. Its members are commonly known as the Sac Fungi. They are the largest phylum of Fungi, with over 64,000 species...
. Aside from yeast anamorphs, and uredinia, aecia and pycnidia, some Basidiomycota form other distinctive anamorphs as parts of their life-cycles. Examples are
Collybia tuberosa with its apple-seed-shaped and coloured
sclerotiumA sclerotium is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until a favorable opportunity for growth. Other fungi that produce...
,
Dendrocollybia racemosa with its sclerotium and its
Tilachlidiopsis racemosa conidia,
Armillaria with their
rhizomorphsMycelial cords are linear aggregations of parallel-oriented hyphae. The mature cords are composed of wide, empty vessel hyphae surrounded by narrower sheathing hyphae...
,
Hohenbuehelia with their
Nematoctonus nematodeThe "roundworms" or "nematodes" are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 80,000 have been described, of which over 15,000 are parasitic. It has been estimated that the total number of...
infectious, state and the coffee leaf parasite,
Mycena citricolorMycena citricolor is a plant pathogen.- External links :* *...
and its
Decapitatus flavidus propaguleIn horticulture, a propagule is any plant material used for the purpose of plant propagation. In asexual reproduction, a propagule may be a woody, semi-hardwood, or softwood cutting, leaf section, or any number of other plant parts. In sexual reproduction, a propagule is a seed or spore...
s called gemmae.
External links