Ascomycota

Ascomycota; Temporal range: EarlyDevonian-present PreꞒ Ꞓ O S D C P T J K Pg N
	Sarcoscypha coccinea
Scientific classification
Domain:	Eukaryota
Kingdom:	Fungi
Subkingdom:	Dikarya
Division:	Ascomycota; (Berk.)Caval.-Sm.(1998)
Subdivisions and classes
	Pezizomycotina Arthoniomycetes Coniocybomycetes Dothideomycetes Eurotiomycetes Geoglossomycetes Laboulbeniomycetes Lecanoromycetes Leotiomycetes Lichinomycetes Omnivoromycetes Orbiliomycetes Pezizomycetes Sordariomycetes Xylonomycetes "Unplaced orders" Lahmiales Itchiclahmadion Triblidiales Saccharomycotina Saccharomycetes Taphrinomycotina Archaeorhizomyces Neolectomycetes Pneumocystidomycetes Schizosaccharomycetes Taphrinomycetes

Ascomycotais aphylumof the kingdomFungithat, together with theBasidiomycota,forms the subkingdomDikarya.Its members are commonly known as thesac fungiorascomycetes.It is the largest phylum of Fungi, with over 64,000species.^[3]The defining feature of this fungal group is the "ascus"(fromAncient Greekἀσκός(askós)'sac, wineskin'), a microscopicsexual structurein which nonmotilespores,calledascospores,are formed. However, some species of Ascomycota areasexualand thus do not form asci or ascospores. Familiar examples of sac fungi includemorels,truffles,brewers'andbakers' yeast,dead man's fingers,andcup fungi.The fungalsymbiontsin the majority oflichens(loosely termed "ascolichens" ) such asCladoniabelong to the Ascomycota.

Ascomycota is amonophyleticgroup (containing all of the descendants of a common ancestor). Previously placed in theBasidiomycotaalong with asexual species from other fungal taxa, asexual (oranamorphic) ascomycetes are now identified and classified based onmorphologicalorphysiologicalsimilarities to ascus-bearingtaxa,and byphylogeneticanalyses ofDNAsequences.^[4]^[5]

Ascomycetes are of particular use to humans as sources of medicinally important compounds such asantibiotics,as well as forfermentingbread, alcoholic beverages, and cheese. Examples of ascomycetes includePenicilliumspecies on cheeses and those producing antibiotics for treating bacterialinfectious diseases.

Many ascomycetes arepathogens,both of animals, including humans, and of plants. Examples of ascomycetes that can cause infections in humans includeCandida albicans,Aspergillus nigerand several tens of species that causeskin infections.The manyplant-pathogenicascomycetes includeapple scab,rice blast,theergotfungi,black knot,and thepowdery mildews.The members of the genusCordycepsareentomopathogenic fungi,meaning that they parasitise and kill insects. Other entomopathogenic ascomycetes have been used successfully inbiological pest control,such asBeauveria.

Several species of ascomycetes are biologicalmodel organismsin laboratory research. Most famously,Neurospora crassa,several species ofyeasts,andAspergillusspecies are used in manygeneticsandcell biologystudies.

Sexual reproduction in ascomycetes

Ascomycetes are 'spore shooters'. They are fungi which produce microscopic spores inside special, elongated cells or sacs, known as 'asci', which give the group its name.

Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid spread of these fungi into new areas. Asexual reproduction of ascomycetes is very diverse from both structural and functional points of view. The most important and general is production of conidia, but chlamydospores are also frequently produced. Furthermore, Ascomycota also reproduce asexually through budding.

Conidia formation

Asexual reproduction may occur through vegetative reproductive spores, theconidia.The asexual, non-motile haploid spores of a fungus, which are named after the Greek word for dust (conia), are hence also known asconidiospores.The conidiospores commonly contain one nucleus and are products of mitotic cell divisions and thus are sometimes calledmitospores,which are genetically identical to the mycelium from which they originate. They are typically formed at the ends of specialized hyphae, the conidiophores. Depending on the species they may be dispersed by wind or water, or by animals. Conidiophores may simply branch off from the mycelia or they may be formed in fruiting bodies.

The hypha that creates the sporing (conidiating) tip can be very similar to the normal hyphal tip, or it can be differentiated. The most common differentiation is the formation of a bottle shaped cell called aphialide,from which the spores are produced. Not all of these asexual structures are a single hypha. In some groups, the conidiophores (the structures that bear the conidia) are aggregated to form a thick structure.

E.g. In the orderMoniliales,all of them are single hyphae with the exception of the aggregations, termed as coremia or synnema. These produce structures rather like corn-stokes, with many conidia being produced in a mass from the aggregated conidiophores.

The diverse conidia and conidiophores sometimes develop in asexual sporocarps with different characteristics (e.g. acervulus, pycnidium, sporodochium). Some species of ascomycetes form their structures within plant tissue, either as parasite or saprophytes. These fungi have evolved more complex asexual sporing structures, probably influenced by the cultural conditions of plant tissue as a substrate. These structures are called thesporodochium.This is a cushion of conidiophores created from a pseudoparenchymatousstromain plant tissue. Thepycnidiumis a globose to flask-shaped parenchymatous structure, lined on its inner wall with conidiophores. Theacervulusis a flat saucer shaped bed of conidiophores produced under a plant cuticle, which eventually erupt through the cuticle for dispersal.

Budding

Asexual reproduction process in ascomycetes also involves the budding which we clearly observe in yeast. This is termed a "blastic process". It involves the blowing out or blebbing of the hyphal tip wall. The blastic process can involve all wall layers, or there can be a new cell wall synthesized which is extruded from within the old wall.

The initial events of budding can be seen as the development of a ring of chitin around the point where the bud is about to appear. This reinforces and stabilizes the cell wall. Enzymatic activity and turgor pressure act to weaken and extrude the cell wall. New cell wall material is incorporated during this phase. Cell contents are forced into the progeny cell, and as the final phase of mitosis ends a cell plate, the point at which a new cell wall will grow inwards from, forms.

Characteristics of ascomycetes

Ascomycota are morphologically diverse. The group includes organisms from unicellular yeasts to complex cup fungi.
98% oflichenshave an Ascomycota as the fungal part of the lichen.^[6]
There are 2000 identified genera and 30,000 species of Ascomycota.
The unifying characteristic among these diverse groups is the presence of a reproductive structure known as theascus,though in some cases it has a reduced role in the life cycle.
Many ascomycetes are of commercial importance. Some play a beneficial role, such as the yeasts used in baking, brewing, and wine fermentation, plus truffles and morels, which are held as gourmet delicacies.
Many of them cause tree diseases, such as Dutch elm disease and apple blights.
Some of the plant pathogenic ascomycetes are apple scab, rice blast, the ergot fungi, black knot, and the powdery mildews.
The yeasts are used to produce alcoholic beverages and breads. The moldPenicilliumis used to produce the antibiotic penicillin.
Almost half of all members of the phylum Ascomycota formsymbioticassociations with algae to form lichens.
Others, such as morels (a highly prized edible fungi), form importantmycorrhizalrelationships with plants, thereby providing enhanced water and nutrient uptake and, in some cases, protection from insects.
Most ascomycetes are terrestrial or parasitic. However, some have adapted to marine or freshwater environments. As of 2015, there were 805marine fungiin the Ascomycota, distributed among 352 genera.^[7]
The cell walls of the hyphae are variably composed ofchitinandβ-glucans,just as in Basidiomycota. However, these fibers are set in a matrix of glycoprotein containing the sugars galactose and mannose.
The mycelium of ascomycetes is usually made up ofseptate hyphae.However, there is not necessarily any fixed number of nuclei in each of the divisions.
The septal walls have septal pores which provide cytoplasmic continuity throughout the individual hyphae. Under appropriate conditions, nuclei may also migrate between septal compartments through the septal pores.
A unique character of the Ascomycota (but not present in all ascomycetes) is the presence ofWoronin bodieson each side of the septa separating the hyphal segments which control the septal pores. If an adjoining hypha is ruptured, the Woronin bodies block the pores to prevent loss of cytoplasm into the ruptured compartment. The Woronin bodies are spherical, hexagonal, or rectangular membrane bound structures with a crystalline protein matrix.

Modern classification

There are threesubphylathat are described and accepted:

ThePezizomycotinaare the largest subphylum and contains all ascomycetes that produceascocarps(fruiting bodies), except for one genus,Neolecta,in theTaphrinomycotina.It is roughly equivalent to the previous taxon,Euascomycetes.The Pezizomycotina includes most macroscopic "ascos" such astruffles,ergot,ascolichens,cup fungi(discomycetes),pyrenomycetes,lorchels,andcaterpillar fungus.^[8]It also contains microscopic fungi such aspowdery mildews,dermatophyticfungi, andLaboulbeniales.
TheSaccharomycotinacomprise most of the "true" yeasts, such asbaker's yeastandCandida,which are single-celled (unicellular) fungi, which reproduce vegetatively by budding. Most of these species were previously classified in a taxon calledHemiascomycetes.
TheTaphrinomycotinainclude a disparate andbasalgroup within the Ascomycota that was recognized following molecular (DNA) analyses. The taxon was originally namedArchiascomycetes(orArchaeascomycetes). It includes hyphal fungi (Neolecta,Taphrina,Archaeorhizomyces), fission yeasts (Schizosaccharomyces), and the mammalian lung parasitePneumocystis.

Outdated taxon names

Several outdated taxon names—based on morphological features—are still occasionally used for species of the Ascomycota. These include the following sexual (teleomorphic) groups, defined by the structures of their sexualfruiting bodies:theDiscomycetes,which included all species formingapothecia;thePyrenomycetes,which included all sac fungi that formedperitheciaorpseudothecia,or any structure resembling these morphological structures; and the Plectomycetes, which included those species that formcleistothecia.Hemiascomycetesincluded the yeasts and yeast-like fungi that have now been placed into theSaccharomycotinaorTaphrinomycotina,while theEuascomycetesincluded the remaining species of the Ascomycota, which are now in thePezizomycotina,and theNeolecta,which are in the Taphrinomycotina.

Some ascomycetes do not reproduce sexually or are not known to produceasciand are thereforeanamorphicspecies. Those anamorphs that produceconidia(mitospores) were previously described asmitosporic Ascomycota.Some taxonomists placed this group into a separateartificial phylum,theDeuteromycota(or "Fungi Imperfecti" ). Where recentmolecular analyseshave identified close relationships with ascus-bearing taxa, anamorphic species have been grouped into the Ascomycota, despite the absence of the defining ascus. Sexual and asexual isolates of the same species commonly carry differentbinomialspecies names, as, for example,Aspergillus nidulansandEmericella nidulans,for asexual and sexual isolates, respectively, of the same species.

Species of the Deuteromycota were classified as Coelomycetes if they produced their conidia in minute flask- or saucer-shaped conidiomata, known technically aspycnidiaandacervuli.^[9]TheHyphomyceteswere those species where theconidiophores(i.e.,the hyphal structures that carry conidia-forming cells at the end) are free or loosely organized. They are mostly isolated but sometimes also appear as bundles of cells aligned in parallel (described assynnematal) or as cushion-shaped masses (described assporodochial).^[10]

Morphology

Most species grow as filamentous, microscopic structures calledhyphaeor as budding single cells (yeasts). Manyinterconnectedhyphae form athallususually referred to as themycelium,which—when visible to the naked eye (macroscopic)—is commonly calledmold.During sexual reproduction, many Ascomycota typically produce large numbers ofasci.The ascus is often contained in a multicellular, occasionally readily visible fruiting structure, theascocarp(also called anascoma). Ascocarps come in a very large variety of shapes: cup-shaped, club-shaped, potato-like, spongy, seed-like, oozing and pimple-like, coral-like, nit-like, golf-ball-shaped, perforated tennis ball-like, cushion-shaped, plated and feathered in miniature (Laboulbeniales), microscopic classic Greek shield-shaped, stalked or sessile. They can appear solitary or clustered. Their texture can likewise be very variable, including fleshy, like charcoal (carbonaceous), leathery, rubbery, gelatinous, slimy, powdery, or cob-web-like. Ascocarps come in multiple colors such as red, orange, yellow, brown, black, or, more rarely, green or blue. Some ascomyceous fungi, such asSaccharomyces cerevisiae,grow as single-celled yeasts, which—during sexual reproduction—develop into an ascus, and do not form fruiting bodies.

Inlichenizedspecies, the thallus of the fungus defines the shape of thesymbioticcolony. Somedimorphicspecies, such asCandida albicans,can switch between growth as single cells and as filamentous, multicellular hyphae. Other species arepleomorphic,exhibiting asexual (anamorphic) as well as a sexual (teleomorphic) growth forms.

Except for lichens, the non-reproductive (vegetative) mycelium of most ascomycetes is usually inconspicuous because it is commonly embedded in the substrate, such as soil, or grows on or inside a living host, and only the ascoma may be seen when fruiting.Pigmentation,such asmelaninin hyphal walls, along with prolific growth on surfaces can result in visible mold colonies; examples includeCladosporiumspecies, which form black spots on bathroom caulking and other moist areas. Many ascomycetes cause food spoilage, and, therefore, the pellicles or moldy layers that develop on jams, juices, and other foods are the mycelia of these species or occasionallyMucoromycotinaand almost neverBasidiomycota.Sooty moldsthat develop on plants, especially in the tropics are the thalli of many species.^{[clarification needed]}

The ascocarp of amorelcontains numerous apothecia.

Large masses of yeast cells, asci or ascus-like cells, or conidia can also form macroscopic structures. For example.Pneumocystisspecies can colonize lung cavities (visible in x-rays), causing a form ofpneumonia.^[11]Asci ofAscosphaerafillhoney bee larvaeandpupaecausing mummification with a chalk-like appearance, hence the name "chalkbrood".^[12]Yeasts for small coloniesin vitroandin vivo,and excessive growth ofCandidaspecies in the mouth or vagina causes "thrush", a form ofcandidiasis.

The cell walls of the ascomycetes almost always containchitinandβ-glucans,and divisions within the hyphae, called "septa",are the internal boundaries of individual cells (or compartments). The cell wall and septa give stability and rigidity to the hyphae and may prevent loss ofcytoplasmin case of local damage to cell wall andcell membrane.The septa commonly have a small opening in the center, which functions as acytoplasmicconnection between adjacent cells, also sometimes allowing cell-to-cell movement ofnucleiwithin a hypha. Vegetative hyphae of most ascomycetes contain only one nucleus per cell (uninucleatehyphae), butmultinucleatecells—especially in the apical regions of growing hyphae—can also be present.

Metabolism

In common with other fungal phyla, the Ascomycota areheterotrophicorganisms that requireorganic compoundsas energy sources. These are obtained by feeding on a variety of organic substrates including dead matter, foodstuffs, or assymbiontsin or on other living organisms. To obtain these nutrients from their surroundings, ascomycetous fungi secrete powerfuldigestive enzymesthat break down organic substances into smaller molecules, which are then taken up into the cell. Many species live on dead plant material such as leaves, twigs, or logs. Several species colonize plants, animals, or other fungi asparasitesormutualistic symbiontsand derive all their metabolic energy in form of nutrients from the tissues of their hosts.

Owing to their long evolutionary history, the Ascomycota have evolved the capacity to break down almost every organic substance. Unlike most organisms, they are able to use their ownenzymesto digest plantbiopolymerssuch ascelluloseorlignin.Collagen,an abundant structural protein in animals, andkeratin—a protein that forms hair and nails—, can also serve as food sources. Unusual examples includeAureobasidium pullulans,which feeds on wall paint, and the kerosene fungusAmorphotheca resinae,which feeds on aircraft fuel (causing occasional problems for the airline industry), and may sometimes block fuel pipes.^[13]Other species can resist highosmotic stressand grow, for example, on salted fish, and a few ascomycetes are aquatic.

The Ascomycota is characterized by a high degree of specialization; for instance, certain species ofLaboulbenialesattack only one particular leg of one particular insect species. Many Ascomycota engage in symbiotic relationships such as in lichens—symbiotic associations with greenalgaeorcyanobacteria—in which the fungal symbiont directly obtains products ofphotosynthesis.In common with many basidiomycetes andGlomeromycota,some ascomycetes form symbioses with plants by colonizing the roots to formmycorrhizalassociations. The Ascomycota also represents severalcarnivorous fungi,which have developed hyphal traps to capture smallprotistssuch asamoebae,as well asroundworms(Nematoda),rotifers,tardigrades,and small arthropods such asspringtails(Collembola).

Distribution and living environment

The Ascomycota are represented in all land ecosystems worldwide, occurring on all continents includingAntarctica.^[14]Spores and hyphal fragments aredispersedthrough the atmosphere and freshwater environments, as well as ocean beaches and tidal zones. The distribution of species is variable; while some are found on all continents, others, as for example the whitetruffleTuber magnatum,only occur in isolated locations in Italy and Eastern Europe.^[15]The distribution of plant-parasitic species is often restricted by host distributions; for example,Cyttariais only found onNothofagus(Southern Beech) in theSouthern Hemisphere.

Reproduction

Asexual reproduction

Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid spread of these fungi into new areas. It occurs through vegetative reproductive spores, theconidia.The conidiospores commonly contain one nucleus and are products ofmitoticcell divisions and thus are sometimes called mitospores, which are genetically identical to the mycelium from which they originate. They are typically formed at the ends of specializedhyphae,theconidiophores.Depending on the species they may bedispersedby wind or water, or by animals.

Asexual spores

Different types of asexual spores can be identified by colour, shape, and how they are released as individual spores. Spore types can be used as taxonomic characters in the classification within the Ascomycota. The most frequent types are the single-celled spores, which are designatedamerospores.If the spore is divided into two by a cross-wall (septum), it is called adidymospore.

Conidiophores of molds of the genusAspergillus;conidiogenesis is blastic-phialidic

When there are two or more cross-walls, the classification depends on spore shape. If the septae aretransversal,like the rungs of a ladder, it is aphragmospore,and if they possess a net-like structure it is adictyospore.Instaurosporesray-like arms radiate from a central body; in others (helicospores) the entire spore is wound up in a spiral like a spring. Very long worm-like spores with a length-to-diameter ratio of more than 15:1, are calledscolecospores.

Conidiogenesis and dehiscence

Important characteristics of the anamorphs of the Ascomycota areconidiogenesis,which includes spore formation and dehiscence (separation from the parent structure). Conidiogenesis corresponds toEmbryologyin animals and plants and can be divided into two fundamental forms of development:blasticconidiogenesis, where the spore is already evident before it separates from the conidiogenic hypha, andthallicconidiogenesis, during which a cross-wall forms and the newly created cell develops into a spore. The spores may or may not be generated in a large-scale specialized structure that helps to spread them.

These two basic types can be further classified as follows:

blastic-acropetal(repeated budding at the tip of the conidiogenic hypha, so that a chain of spores is formed with the youngest spores at the tip),
blastic-synchronous(simultaneous spore formation from a central cell, sometimes with secondary acropetal chains forming from the initial spores),
blastic-sympodial(repeated sideways spore formation from behind the leading spore, so that the oldest spore is at the main tip),
blastic-annellidic(each spore separates and leaves a ring-shaped scar inside the scar left by the previous spore),
blastic-phialidic(the spores arise and are ejected from the open ends of special conidiogenic cells calledphialides,which remain constant in length),
basauxic(where a chain of conidia, in successively younger stages of development, is emitted from the mother cell),
blastic-retrogressive(spores separate by formation of crosswalls near the tip of the conidiogenic hypha, which thus becomes progressively shorter),
thallic-arthric(double cell walls split the conidiogenic hypha into cells that develop into short, cylindrical spores calledarthroconidia;sometimes every second cell dies off, leaving the arthroconidia free),
thallic-solitary(a large bulging cell separates from the conidiogenic hypha, forms internal walls, and develops to aphragmospore).

Sometimes the conidia are produced in structures visible to the naked eye, which help to distribute the spores. These structures are called "conidiomata" (singular:conidioma), and may take the form ofpycnidia(which are flask-shaped and arise in the fungal tissue) oracervuli(which are cushion-shaped and arise in host tissue).

Dehiscence happens in two ways. Inschizolyticdehiscence, a double-dividing wall with a central lamella (layer) forms between the cells; the central layer then breaks down thereby releasing the spores. Inrhexolyticdehiscence, the cell wall that joins the spores on the outside degenerates and releases the conidia.

Heterokaryosis and parasexuality

Several Ascomycota species are not known to have a sexual cycle. Such asexual species may be able to undergo genetic recombination between individuals by processes involvingheterokaryosisandparasexualevents.

Parasexuality refers to the process of heterokaryosis,^[16]caused by merging of two hyphae belonging to different individuals, by a process calledanastomosis,followed by a series of events resulting in genetically differentcell nucleiin themycelium.^[17] The merging of nuclei is not followed bymeiotic events,such asgameteformation and results in an increased number ofchromosomesper nuclei.Mitotic crossovermay enablerecombination,i.e., an exchange of genetic material betweenhomologous chromosomes.The chromosome number may then be restored to itshaploidstate bynuclear division,with each daughter nuclei being genetically different from the original parent nuclei.^[18]Alternatively, nuclei may lose some chromosomes, resulting inaneuploidcells.Candida albicans(class Saccharomycetes) is an example of a fungus that has a parasexual cycle (seeCandida albicansandParasexual cycle).

Sexual reproduction

Ascus ofHypocrea virenswith eight two-celled Ascospores

Sexual reproduction in the Ascomycota leads to the formation of theascus,the structure that defines this fungal group and distinguishes it from other fungal phyla. The ascus is a tube-shaped vessel, ameiosporangium,which contains the sexual spores produced bymeiosisand which are calledascospores.

Apart from a few exceptions, such asCandida albicans,most ascomycetes arehaploid,i.e., they contain one set ofchromosomesper nucleus. During sexual reproduction there is adiploidphase, which commonly is very short, and meiosis restores the haploid state. The sexual cycle of one well-studied representative species of Ascomycota is described in greater detail inNeurospora crassa.Also, the adaptive basis for the maintenance of sexual reproduction in the Ascomycotafungiwas reviewed by Wallen and Perlin.^[19]They concluded that the most plausible reason for the maintenance of this capability is the benefit ofrepairing DNA damageby usingrecombinationthat occurs duringmeiosis.^[19]DNA damage can be caused by a variety of stresses such as nutrient limitation.

Formation of sexual spores

The sexual part of the life cycle commences when two hyphal structuresmate.In the case ofhomothallicspecies, mating is enabled between hyphae of the same fungalclone,whereas inheterothallicspecies, the two hyphae must originate from fungal clones that differ genetically, i.e., those that are of a differentmating type.Mating types are typical of the fungi and correspond roughly to the sexes in plants and animals; however one species may have more than two mating types, resulting in sometimes complexvegetative incompatibilitysystems. Theadaptive function of mating typeis discussed inNeurospora crassa.

Gametangiaare sexual structures formed from hyphae, and are the generative cells. A very fine hypha, calledtrichogyneemerges from one gametangium, theascogonium,and merges with a gametangium (theantheridium) of the other fungal isolate. The nuclei in the antheridium then migrate into the ascogonium, andplasmogamy—the mixing of thecytoplasm—occurs. Unlike in animals and plants, plasmogamy is not immediately followed by the merging of the nuclei (calledkaryogamy). Instead, the nuclei from the two hyphae form pairs, initiating thedikaryophaseof the sexual cycle, during which time the pairs of nuclei synchronously divide. Fusion of the paired nuclei leads to mixing of the genetic material andrecombinationand is followed bymeiosis.A similar sexual cycle is present in thered algae(Rhodophyta). A discarded hypothesis held that a second karyogamy event occurred in the ascogonium prior to ascogeny, resulting in a tetraploid nucleus which divided into four diploid nuclei by meiosis and then into eight haploid nuclei by a supposed process calledbrachymeiosis,but this hypothesis was disproven in the 1950s.^[20]

From the fertilized ascogonium,dinucleatehyphae emerge in which each cell contains two nuclei. These hyphae are calledascogenousor fertile hyphae. They are supported by the vegetative mycelium containing uni– (or mono–) nucleate hyphae, which are sterile. The mycelium containing both sterile and fertile hyphae may grow into fruiting body, theascocarp,which may contain millions of fertile hyphae.

An ascocarp is the fruiting body of the sexual phase in Ascomycota. There are five morphologically different types of ascocarp, namely:

Naked asci: these occur in simple ascomycetes; asci are produced on the organism's surface.
Perithecia:Asci are in flask-shaped ascoma (perithecium) with a pore (ostiole) at the top.
Cleistothecia:The ascocarp (a cleistothecium) is spherical and closed.
Apothecia:The asci are in a bowl shaped ascoma (apothecium). These are sometimes called the "cup fungi".
Pseudothecia:Asci with two layers, produced in pseudothecia that look like perithecia. The ascospores are arranged irregularly.^[21]

The sexual structures are formed in the fruiting layer of the ascocarp, thehymenium.At one end of ascogenous hyphae, characteristic U-shaped hooks develop, which curve back opposite to the growth direction of the hyphae. The two nuclei contained in the apical part of each hypha divide in such a way that the threads of theirmitotic spindlesrun parallel, creating two pairs of genetically different nuclei. One daughter nucleus migrates close to the hook, while the other daughter nucleus locates to the basal part of the hypha. The formation of two parallel cross-walls then divides the hypha into three sections: one at the hook with one nucleus, one at the basal of the original hypha that contains one nucleus, and one that separates the U-shaped part, which contains the other two nuclei.

Cross-section of a cup-shaped structure showing locations of developing meiotic asci (upper edge of cup, left side, arrows pointing to two gray-colored cells containing four and two small circles), sterile hyphae (upper edge of cup, right side, arrows pointing to white-colored cells with a single small circle in them), and mature asci (upper edge of cup, pointing to two gray-colored cells with eight small circles in them) — Diagram of anapothecium(the typical cup-like reproductive structure of ascomycetes) showing sterile tissues as well as developing and mature asci.

Fusion of the nuclei (karyogamy) takes place in the U-shaped cells in the hymenium, and results in the formation of a diploidzygote.The zygote grows into theascus,an elongated tube-shaped or cylinder-shaped capsule. Meiosis then gives rise to fourhaploidnuclei, usually followed by a further mitotic division that results in eight nuclei in each ascus. The nuclei along with some cytoplasma become enclosed within membranes and a cell wall to give rise to ascospores that are aligned inside the ascus like peas in a pod.

Upon opening of the ascus, ascospores may be dispersed by the wind, while in some cases the spores are forcibly ejected form the ascus; certain species have evolved spore cannons, which can eject ascospores up to 30 cm. away. When the spores reach a suitable substrate, they germinate, form new hyphae, which restarts the fungal life cycle.

The form of the ascus is important for classification and is divided into four basic types: unitunicate-operculate, unitunicate-inoperculate, bitunicate, or prototunicate. See the article onascifor further details.

Ecology

The Ascomycota fulfil a central role in most land-basedecosystems.They are importantdecomposers,breaking down organic materials, such as dead leaves and animals, and helping thedetritivores(animals that feed on decomposing material) to obtain their nutrients. Ascomycetes, along with other fungi, can break down largemoleculessuch ascelluloseorlignin,and thus have important roles in nutrient cycling such as thecarbon cycle.

The fruiting bodies of the Ascomycota provide food for many animals ranging frominsectsand slugs and snails (Gastropoda) torodentsand larger mammals such asdeerandwild boars.

Many ascomycetes also formsymbioticrelationships with other organisms, including plants and animals.

Lichens

Probably since early in their evolutionary history, the Ascomycota have formed symbiotic associations withgreen algae(Chlorophyta), and other types ofalgaeandcyanobacteria.These mutualistic associations are commonly known aslichens,and can grow and persist in terrestrial regions of the earth that are inhospitable to other organisms and characterized by extremes in temperature and humidity, including theArctic,theAntarctic,deserts,and mountaintops. While thephotoautotrophicalgal partner generates metabolic energy through photosynthesis, the fungus offers a stable, supportive matrix and protects cells from radiation and dehydration. Around 42% of the Ascomycota (about 18,000 species) form lichens, and almost all the fungal partners of lichens belong to the Ascomycota.

Mycorrhizal fungi and endophytes

Members of the Ascomycota form two important types of relationship with plants: asmycorrhizalfungi and asendophytes.Mycorrhiza aresymbioticassociations of fungi with the root systems of the plants, which can be of vital importance for growth and persistence for the plant. The fine mycelial network of the fungus enables the increased uptake of mineral salts that occur at low levels in the soil. In return, the plant provides the fungus with metabolic energy in the form ofphotosyntheticproducts.

Endophytic fungi live inside plants, and those that form mutualistic orcommensalassociations with their host, do not damage their hosts. The exact nature of the relationship between endophytic fungus and host depends on the species involved, and in some cases fungal colonization of plants can bestow a higher resistance against insects,roundworms(nematodes), andbacteria;in the case ofgrass endophytesthe fungal symbiont produces poisonousalkaloids,which can affect the health of plant-eating (herbivorous)mammalsand deter or kill insect herbivores.^[22]

Symbiotic relationships with animals

Several ascomycetes of the genusXylariacolonize the nests ofleafcutter antsand otherfungus-growing antsof the tribeAttini,and the fungal gardens oftermites(Isoptera). Since they do not generate fruiting bodies until the insects have left the nests, it is suspected that, as confirmed in several cases ofBasidiomycotaspecies, they may be cultivated.^{[clarification needed]}

Bark beetles(family Scolytidae) are important symbiotic partners of ascomycetes. The female beetles transport fungal spores to new hosts in characteristic tucks in their skin, themycetangia.The beetle tunnels into the wood and into large chambers in which they lay their eggs. Spores released from the mycetangia germinate into hyphae, which can break down the wood. The beetle larvae then feed on the fungal mycelium, and, on reaching maturity, carry new spores with them to renew the cycle of infection. A well-known example of this isDutch elm disease,caused byOphiostoma ulmi,which is carried by the European elm bark beetle,Scolytus multistriatus.^[23]

Plant disease interactions

One of their most harmful roles is as the agent of many plant diseases. For instance:

Dutch elm disease,caused by the closely related speciesOphiostoma ulmiandOphiostoma novo-ulmi,has led to the death of many elms in Europe and North America.
The originally AsianCryphonectria parasiticais responsible for attacking Sweet Chestnuts (Castanea sativa), and virtually eliminated the once-widespreadAmerican Chestnut(Castanea dentata),
A disease ofmaize(Zea mays), which is especially prevalent in North America, is brought about byCochliobolus heterostrophus.
Taphrina deformanscausesleaf curlof peach.
Uncinula necatoris responsible for the diseasepowdery mildew,which attacks grapevines.
Species ofMoniliniacause brown rot of stone fruit such as peaches (Prunus persica) and sour cherries (Prunus ceranus).
Members of the Ascomycota such asStachybotrys chartarumare responsible for fading of woolen textiles, which is a common problem especially in the tropics.
Blue-green, red and brownmoldsattack and spoil foodstuffs – for instancePenicillium italicumrots oranges.
Cereals infected withFusarium graminearumcontainmycotoxinslikedeoxynivalenol(DON), which causesFusarium ear blightand skin and mucous membrane lesions when eaten by pigs.

Human disease interactions

Aspergillus fumigatus,the most common cause of fungal infection in the lungs of immune-compromised patients often resulting in death. Also the most frequent cause ofAllergic bronchopulmonary aspergillosis,which often occurs in patients withCystic fibrosisas well asAsthma.
Candida albicans,a yeast that attacks the mucous membranes, can cause an infection of the mouth or vagina called thrush orcandidiasis,and is also blamed for "yeast allergies".
Fungi likeEpidermophytoncause skin infections but are not very dangerous for people with healthy immune systems. However, if the immune system is damaged they can be life-threatening; for instance,Pneumocystis jiroveciiis responsible for severe lung infections that occur inAIDSpatients.
Ergot(Claviceps purpurea) is a direct menace to humans when it attacks wheat or rye and produces highly poisonousalkaloids,causingergotismif consumed. Symptoms include hallucinations, stomach cramps, and a burning sensation in the limbs ( "Saint Anthony's Fire").
Aspergillus flavus,which grows on peanuts and other hosts, generatesaflatoxin,which damages the liver and is highly carcinogenic.
Histoplasma capsulatumcauses histoplasmosis, which affects immunocompromised patients.
Blastomyces dermatitidisis the causal agent of blastomycosis, an invasive and often serious fungal infection found occasionally in humans and other animals in regions where the fungus is endemic.
Paracoccidioides brasiliensisandParacoccidioides lutziiare the causal agents ofparacoccidioidomycosis.
Coccidioides immitisandCoccidioides posadasiiare the causative agent ofcoccidioidomycosis(valley fever).
Talaromyces marneffei,formerly calledPenicillium marneffeicausestalaromycosis

Beneficial effects for humans

On the other hand, ascus fungi have brought some important benefits to humanity.

The most famous case may be that of the moldPenicillium chrysogenum(formerlyPenicillium notatum), which, probably to attack competing bacteria, produces an antibiotic that, under the name ofpenicillin,triggered a revolution in the treatment of bacterial infectious diseases in the 20th century.
The medical importance ofTolypocladium niveumas animmunosuppressorcan hardly be exaggerated. It excretesCiclosporin,which, as well as being given duringOrgan transplantationto prevent rejection, is also prescribed for auto-immune diseases such asmultiple sclerosis,although there is some doubt over the long-term side-effects of the treatment.

Some ascomycete fungi can be altered relatively easily throughgenetic engineeringprocedures. They can then produce useful proteins such asinsulin,human growth hormone,or TPa, which is employed to dissolve blood clots.
Several species are commonmodel organismsin biology, includingSaccharomyces cerevisiae,Schizosaccharomyces pombe,andNeurospora crassa.Thegenomesof a number of ascomycete fungi have been fully sequenced.
Baker's Yeast (Saccharomyces cerevisiae) is used to makebread,beerandwine,during which process sugars such asglucoseorsucroseare fermented to makeethanolandcarbon dioxide.Bakers use the yeast for carbon dioxide production, causing the bread to rise, with the ethanol boiling off during cooking. Most vintners use it for ethanol production, with the carbon dioxide being released into the atmosphere during fermentation. Brewers and traditional producers ofsparkling wineuse both, with a primary fermentation for the alcohol and a secondary one to produce the carbon dioxide bubbles that provide the drinks with "sparkling" texture in the case of wine and the desirable foam in the case of beer.
Enzymes ofPenicillium camembertiplay a role in the manufacture of the cheesesCamembertandBrie,while those ofPenicillium roquefortido the same forGorgonzola,RoquefortandStilton.
In Asia,Aspergillus oryzaeis added to a pulp of soaked soya beans to makesoy sauce,and is used to break down starch in rice and other grains into simple sugars for fermentation into East Asian alcoholic beverages such ashuangjiuandsake.
Finally, some members of the Ascomycota are choice edibles;morels(Morchella spp.),truffles(Tuber spp.), andlobster mushroom(Hypomyces lactifluorum) are some of the most sought-after fungal delicacies.
Cordyceps militarisis known for its numerous medicinal benefits, including supporting the immune system, reducing inflammation, providing antioxidant effects, enhancing metabolic health, improving athletic performance, and promoting respiratory health. It contains bioactive compounds such ascordycepin,cordycepic acid,adenosine,andpolysaccharides,beta-glucans,andergosterol.^[24]^[25]^[26]

Notes

^Taylor, TN; Hass, H; Kerp, H; Krings, M; Hanlin, RT (2005)."Perithecial ascomycetes from the 400 million year old Rhynie chert: an example of ancestral polymorphism"(PDF).Mycologia.97(1): 269–285.doi:10.3852/mycologia.97.1.269.hdl:1808/16786.PMID 16389979.
^Cavalier-Smith, T. (August 1998). "A revised six-kingdom system of life".Biological Reviews.73(3): 203–266.doi:10.1111/j.1469-185X.1998.tb00030.x.PMID 9809012.S2CID 6557779.
^Kirket al., p. 55.
^Lutzoni F; et al. (2004)."Assembling the fungal tree of life: progress, classification, and evolution of subcellular traits".American Journal of Botany.91(10): 1446–80.doi:10.3732/ajb.91.10.1446.PMID 21652303.
^James TY; et al. (2006). "Reconstructing the early evolution of Fungi using a six-gene phylogeny".Nature.443(7113): 818–22.Bibcode:2006Natur.443..818J.doi:10.1038/nature05110.PMID 17051209.S2CID 4302864.
^McCoy, Peter (2016).Radical Mycology.Chthaeus Press.ISBN 9780986399602.
^Jones, E.B. Gareth; Suetrong, Satinee; Sakayaroj, Jariya; Bahkali, Ali H.; Abdel-Wahab, Mohamed A.; Boekhout, Teun; Pang, Ka-Lai (2015). "Classification of marine Ascomycota, Basidiomycota, Blastocladiomycota and Chytridiomycota".Fungal Diversity.73(1): 1–72.doi:10.1007/s13225-015-0339-4.S2CID 38469033.
^"Caterpillar Fungus".Archived fromthe originalon 12 March 2007.
^Alexopoulos, Mims & Blackwell 1996,p. 233
^Alexopoulos, Mims & Blackwell 1996,pp. 218–222
^Krajicek BJ, Thomas CF Jr, Limper AH (2009). "Pneumocystispneumonia: current concepts in pathogenesis, diagnosis, and treatment ".Clinics in Chest Medicine.30(2): 265–89.doi:10.1016/j.ccm.2009.02.005.PMID 19375633.
^James, R.R.; Skinner, J.S. (October 2005). "PCR diagnostic methods for Ascosphaera infections in bees".Journal of Invertebrate Pathology.90(2): 98–103.Bibcode:2005JInvP..90...98J.doi:10.1016/j.jip.2005.08.004.PMID 16214164.
^Hendey, N. I. (1964). "Some observations on Cladosporium resinae as a fuel contaminant and its possible role in the corrosion of aluminium alloy fuel tanks".Transactions of the British Mycological Society.47(7): 467–475.doi:10.1016/s0007-1536(64)80024-3.
^Laybourn-Parry J., J (2009). "Microbiology. No place too cold".Science.324(5934): 1521–22.Bibcode:2009Sci...324.1521L.doi:10.1126/science.1173645.PMID 19541982.S2CID 33598792.
^Mello A, Murat, Bonfante P (2006)."Truffles: much more than a prized and local fungal delicacy".FEMS Microbiology Letters.260(1): 1–8.doi:10.1111/j.1574-6968.2006.00252.x.PMID 16790011.
^Cole, Garry T. (1996)."Basic Biology of Fungi".Medical Microbiology(4th ed.). University of Texas Medical Branch at Galveston.ISBN 978-0-9631172-1-2.
^Deacon 2005,pp. 164–6
^Deacon 2005,pp. 167–8
^^a ^bWallen RM, Perlin MH (2018)."An Overview of the Function and Maintenance of Sexual Reproduction in Dikaryotic Fungi".Front Microbiol.9:503.doi:10.3389/fmicb.2018.00503.PMC5871698.PMID 29619017.
^Carlile, Michael J. (2005). "Two influential mycologists: Helen Gwynne-Vaughan (1879–1967) and Lilian Hawker (1908–1991)".Mycologist.19(3): 129–131.doi:10.1017/s0269915x05003058.
^"Ascomycota – Characteristics, Nutrition and Significance".MicroscopeMaster.Retrieved4 March2019.
^Schulz B, Boyle C., B; Boyle, C (2005). "The endophytic continuum".Mycological Research.109(6): 661–86.doi:10.1017/S095375620500273X.PMID 16080390.
^Moser, John C.; Konrad, Heino; Blomquist, Stacy R.; Kirisits, Thomas (February 2010)."Do mites phoretic on elm bark beetles contribute to the transmission of Dutch elm disease?".Naturwissenschaften.97(2): 219–227.Bibcode:2010NW.....97..219M.doi:10.1007/s00114-009-0630-x.PMID 19967528.S2CID 15554606.
^Abdullah, Salik; Kumar, Abhinandan (June 2023)."A brief review on the medicinal uses of Cordyceps militaris".Pharmacological Research – Modern Chinese Medicine.7:100228.doi:10.1016/j.prmcm.2023.100228.
^Das, Gitishree; Shin, Han-Seung; Leyva-Gómez, Gerardo; Prado-Audelo, María L. Del; Cortes, Hernán; Singh, Yengkhom Disco; Panda, Manasa Kumar; Mishra, Abhay Prakash; Nigam, Manisha; Saklani, Sarla; Chaturi, Praveen Kumar; Martorell, Miquel; Cruz-Martins, Natália; Sharma, Vineet; Garg, Neha; Sharma, Rohit; Patra, Jayanta Kumar (8 February 2021)."Cordyceps spp.: A Review on Its Immune-Stimulatory and Other Biological Potentials".Frontiers in Pharmacology.11.doi:10.3389/fphar.2020.602364.PMC7898063.PMID 33628175.
^Zhang, Danyu; Tang, Qingjiu; He, Xianzhe; Wang, Yipeng; Zhu, Guangyong; Yu, Ling (8 September 2023)."Antimicrobial, antioxidant, anti-inflammatory, and cytotoxic activities of Cordyceps militaris spent substrate".PLOS ONE.18(9): e0291363.Bibcode:2023PLoSO..1891363Z.doi:10.1371/journal.pone.0291363.PMC10490986.PMID 37682981.

Cited texts

Alexopoulos, C.J.; Mims, C.W.; Blackwell, M. (1996).Introductory Mycology.Wiley.ISBN 0-471-52229-5.
Deacon, J. (2005).Fungal Biology.Blackwell.ISBN 1-4051-3066-0.
Jennings DH, Lysek G (1996).Fungal Biology: Understanding the Fungal Lifestyle.Guildford, UK: Bios Scientific.ISBN 978-1-85996-150-6.
Kirk PM, Cannon PF, Minter DW, Stalpers JA (2008).Dictionary of the Fungi(10th ed.). Wallingford: CABI.ISBN 978-0-85199-826-8.
Taylor EL, Taylor TN (1993).The Biology and Evolution of Fossil Plants.Prentice Hall.ISBN 0-13-651589-4.

[1] Taylor, TN; Hass, H; Kerp, H; Krings, M; Hanlin, RT (2005)."Perithecial ascomycetes from the 400 million year old Rhynie chert: an example of ancestral polymorphism"(PDF).Mycologia.97(1): 269–285.doi:10.3852/mycologia.97.1.269.hdl:1808/16786.PMID 16389979.

[2] Cavalier-Smith, T. (August 1998). "A revised six-kingdom system of life".Biological Reviews.73(3): 203–266.doi:10.1111/j.1469-185X.1998.tb00030.x.PMID 9809012.S2CID 6557779.

[3] Kirket al., p. 55.

[Lutzoni_2004-4] Lutzoni F; et al. (2004)."Assembling the fungal tree of life: progress, classification, and evolution of subcellular traits".American Journal of Botany.91(10): 1446–80.doi:10.3732/ajb.91.10.1446.PMID 21652303.

[James_2006-5] James TY; et al. (2006). "Reconstructing the early evolution of Fungi using a six-gene phylogeny".Nature.443(7113): 818–22.Bibcode:2006Natur.443..818J.doi:10.1038/nature05110.PMID 17051209.S2CID 4302864.

[6] McCoy, Peter (2016).Radical Mycology.Chthaeus Press.ISBN 9780986399602.

[Jones_et_al._2015-7] Jones, E.B. Gareth; Suetrong, Satinee; Sakayaroj, Jariya; Bahkali, Ali H.; Abdel-Wahab, Mohamed A.; Boekhout, Teun; Pang, Ka-Lai (2015). "Classification of marine Ascomycota, Basidiomycota, Blastocladiomycota and Chytridiomycota".Fungal Diversity.73(1): 1–72.doi:10.1007/s13225-015-0339-4.S2CID 38469033.

[8] "Caterpillar Fungus".Archived fromthe originalon 12 March 2007.

[9] Alexopoulos, Mims & Blackwell 1996,p. 233

[10] Alexopoulos, Mims & Blackwell 1996,pp. 218–222

[11] Krajicek BJ, Thomas CF Jr, Limper AH (2009). "Pneumocystispneumonia: current concepts in pathogenesis, diagnosis, and treatment ".Clinics in Chest Medicine.30(2): 265–89.doi:10.1016/j.ccm.2009.02.005.PMID 19375633.

[12] James, R.R.; Skinner, J.S. (October 2005). "PCR diagnostic methods for Ascosphaera infections in bees".Journal of Invertebrate Pathology.90(2): 98–103.Bibcode:2005JInvP..90...98J.doi:10.1016/j.jip.2005.08.004.PMID 16214164.

[Hendey-13] Hendey, N. I. (1964). "Some observations on Cladosporium resinae as a fuel contaminant and its possible role in the corrosion of aluminium alloy fuel tanks".Transactions of the British Mycological Society.47(7): 467–475.doi:10.1016/s0007-1536(64)80024-3.

[14] Laybourn-Parry J., J (2009). "Microbiology. No place too cold".Science.324(5934): 1521–22.Bibcode:2009Sci...324.1521L.doi:10.1126/science.1173645.PMID 19541982.S2CID 33598792.

[15] Mello A, Murat, Bonfante P (2006)."Truffles: much more than a prized and local fungal delicacy".FEMS Microbiology Letters.260(1): 1–8.doi:10.1111/j.1574-6968.2006.00252.x.PMID 16790011.

[16] Cole, Garry T. (1996)."Basic Biology of Fungi".Medical Microbiology(4th ed.). University of Texas Medical Branch at Galveston.ISBN 978-0-9631172-1-2.

[17] Deacon 2005,pp. 164–6

[18] Deacon 2005,pp. 167–8

[pmid29619017-19] Wallen RM, Perlin MH (2018)."An Overview of the Function and Maintenance of Sexual Reproduction in Dikaryotic Fungi".Front Microbiol.9:503.doi:10.3389/fmicb.2018.00503.PMC5871698.PMID 29619017.

[Carlile-20] Carlile, Michael J. (2005). "Two influential mycologists: Helen Gwynne-Vaughan (1879–1967) and Lilian Hawker (1908–1991)".Mycologist.19(3): 129–131.doi:10.1017/s0269915x05003058.

[21] "Ascomycota – Characteristics, Nutrition and Significance".MicroscopeMaster.Retrieved4 March2019.

[22] Schulz B, Boyle C., B; Boyle, C (2005). "The endophytic continuum".Mycological Research.109(6): 661–86.doi:10.1017/S095375620500273X.PMID 16080390.

[Moser_2010-23] Moser, John C.; Konrad, Heino; Blomquist, Stacy R.; Kirisits, Thomas (February 2010)."Do mites phoretic on elm bark beetles contribute to the transmission of Dutch elm disease?".Naturwissenschaften.97(2): 219–227.Bibcode:2010NW.....97..219M.doi:10.1007/s00114-009-0630-x.PMID 19967528.S2CID 15554606.

[24] Abdullah, Salik; Kumar, Abhinandan (June 2023)."A brief review on the medicinal uses of Cordyceps militaris".Pharmacological Research – Modern Chinese Medicine.7:100228.doi:10.1016/j.prmcm.2023.100228.

[25] Das, Gitishree; Shin, Han-Seung; Leyva-Gómez, Gerardo; Prado-Audelo, María L. Del; Cortes, Hernán; Singh, Yengkhom Disco; Panda, Manasa Kumar; Mishra, Abhay Prakash; Nigam, Manisha; Saklani, Sarla; Chaturi, Praveen Kumar; Martorell, Miquel; Cruz-Martins, Natália; Sharma, Vineet; Garg, Neha; Sharma, Rohit; Patra, Jayanta Kumar (8 February 2021)."Cordyceps spp.: A Review on Its Immune-Stimulatory and Other Biological Potentials".Frontiers in Pharmacology.11.doi:10.3389/fphar.2020.602364.PMC7898063.PMID 33628175.

[26] Zhang, Danyu; Tang, Qingjiu; He, Xianzhe; Wang, Yipeng; Zhu, Guangyong; Yu, Ling (8 September 2023)."Antimicrobial, antioxidant, anti-inflammatory, and cytotoxic activities of Cordyceps militaris spent substrate".PLOS ONE.18(9): e0291363.Bibcode:2023PLoSO..1891363Z.doi:10.1371/journal.pone.0291363.PMC10490986.PMID 37682981.

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