Ascomycota 48981 221725868 2008-06-25T20:31:01Z DOI bot 6652755 Citation maintenance. Added: doi_brokendate. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. {{Nofootnotes|date=March 2008}} {{Taxobox | name = Ascomycetes | image = Scarlet elf cap cadnant dingle.jpg | image_width = 238px | image_caption = ''Sarcoscypha austriaca'' | regnum = [[Fungus|Fungi]] | subregnum = [[Dikarya]] | phylum = '''Ascomycota''' | phylum_authority = (Berk 1857) Caval.-Sm. 1998<ref>{{cite journal | author=Cavalier-Smith, T. | year = 1998 | title = A revised six-kingdom system of Life | journal = [[Biol. Rev. Camb. Philos. Soc.]] | volume = 73 | issue = 3 | pages = 203–266 | url = http://journals.cambridge.org/action/displayIssue?jid=BRE&volumeId=73&issueId=03# | doi = 10.1017/S0006323198005167}}</ref> | subdivision_ranks = Subphyla/Classes | subdivision = :[[Pezizomycotina]] {{Ref_label<!--1-->|Taylor_1996|1|a}}{{Ref_label<!--4-->||4|d}} ::[[Laboulbeniomycetes]] ::[[Eurotiomycetes]] ::[[Lecanoromycetes]] ::[[Leotiomycetes]] ::[[Pezizomycetes]] ::[[Sordariomycetes]] ::[[Dothideomycetes]] ::[[Lichinomycetes]] ::[[Arthoniomycetes]] ::[[Orbilomycetes]] ::"Unplaced orders" ::::[[Lahmiales]] ::::[[Medeolariales]] ::::[[Triblidiales]] :[[Saccharomycotina]] ::[[Saccharomycetes]] :[[Taphrinomycotina]] ::[[Neolectomycetes]] ::[[Pneumocystis|Pneumocystidomycetes]] ::[[Schizosaccharomycetes]] ::[[Taphrinomycetes]] }} '''Ascomycota''' is a [[Division (botany)|Division]]/[[Phylum]] of [[Fungi]], and subkingdom [[Dikarya]], whose members are commonly known as the '''Sac Fungi'''. Characteristically, when reproducing sexually, they produce nonmotile [[spore]]s in a distinctive type of microscopic [[cell (biology)|cell]] called an "[[ascus]]" (from [[Greek language|Greek]]: ''{{polytonic|ἀσκός}}'' (''askos''), meaning "sac" or "wineskin"). These spores are called [[ascospores]]. However, some members of the Ascomycota do not reproduce sexually and do not form asci or ascospores. These members are assigned to Ascomycota based upon [[morphology (biology)|morphological]] and/or [[physiological]] similarities to ascus-bearing taxa, and in particular by [[phylogenetic]] comparisons of [[DNA]] sequences.<ref name=Lutzoni_2004>{{cite journal | author=Lutzoni F, et al | title= Assembling the fungal tree of life: progress, classification, and evolution of subcellular traits | journal=Amer J Bot | year=2004 | pages=1446–1480 | volume=91 | doi = 10.3732/ajb.91.10.1446 <!--Retrieved from CrossRef by DOI bot--> | doi_brokendate= 2008-06-25}}</ref><ref name=James_2006>{{cite journal | author=James TY et al | title=Reconstructing the early evolution of Fungi using a six-gene phylogeny | journal=Nature | year=2006 | pages=818–822 | volume=443 | pmid=17051209 | doi = 10.1038/nature05110 <!--Retrieved from CrossRef by DOI bot--> | doi_brokendate=2008-06-25}}</ref> This [[monophyletic]] grouping is an extremely significant and successful group of organisms. Familiar examples of sac fungi include [[morel]]s, [[Tuber (genus)|truffles]], [[brewer's yeast]] and [[baker's yeast]], [[Xylaria|Dead Man's Fingers]], [[cup fungi]], and the majority of [[lichen]]s (loosely termed [[lichen|"ascolichens"]]) such as ''[[Cladonia]]''. Many plant-pathogenic fungi belong to the Ascomycota. Commonly seen examples include [[apple scab]], [[ergot]], [[black knot]], and the [[powdery mildew]]s. Species of ascomycetes are also popular in the laboratory. ''[[Sordaria fimicola]]'', ''[[Neurospora crassa]]'' and several species of [[yeast]]s are used in many [[genetics]] and [[cell biology]] experiments. ''[[Penicillium]]'' species on cheeses and in the antibiotic industry are examples of [[asexual (fungus)|asexual]] [[taxa]], otherwise known as [[anamorph]]s, that belong in the Ascomycota. Prior to definitive phylogenetic research, molds such as ''[[Penicillium]]'' were sometimes classified in an artificial phylum, called the [[Deuteromycota]]. == Ascomycetes versus Ascomycota {{Ref_label<!--4-->||4|d}} == In the past, before the recognition of the [[Fungi|fungal kingdom]], the sac fungi were considered to be a [[Class (biology)|''Class'']], not a ''[[Phylum]]''. The original collective term for them was "Ascomycetes", a label first coined in the 1800s for a rankless nonlichenized [[taxon]] based upon the presence of asci. "Ascomycetes" was soon used to include lichenized taxa, and became the standard term, at the class level, for all ascus-bearing species, just as the term "[[Basidiomycetes]]" became used for their basidium-bearing counterparts. Elevation of the taxonomic rank of the Ascomycetes resulted in the names Ascomycetae, Ascomycotina, and finally Ascomycota. The names Ascomycota, Ascomycetes, etc. are based upon the term "ascus". Together, the Ascomycota and the Basidiomycota form the subkingdom [[Dikarya]]. The more familiar term, Ascomycetes, is still loosely used, e.g. at fungal forays it is often said of a fungus, such as ''[[Peziza]]'', "It is an ascomycete, not a basidiomycete" in reference to their sexual reproductive mode. The terms are further abbreviated to "ascos" and "basidos" which are not officially sanctioned technical names. == Modern classification of Ascomycota == There are 3 subphyla: *The subphylum '''[[Pezizomycotina]]''' is the largest subphylum and contains all the Ascomycota that produce [[ascocarp]]s (fruiting bodies), except for one genus, ''Neolecta'', in the Taphrinomycotina. Therefore, it includes virtually all macroscopic "ascos" such as {{dn|Truffles|truffles}}, [[ergot]], ascolichens, cup fungi (discomycetes), pyrenomycetes, [[lorchels]], and [[caterpillar fungus]][http://www.herbarium.usu.edu/fungi/FunFacts/Caterpillar.htm], as well as many microscopic fungi, e.g. [[powdery mildew]]s, [[ring worm]] fungi, [[chalkbrood]] fungus[http://maarec.cas.psu.edu/pest&disease/slide25.htm], [[Laboulbeniales]], and most black molds around sinks and tubs. The older named taxon '''Euascomycetes''' is roughly equivalent. *The subphylum '''[[Saccharomycotina]]''' comprises most of the "true" yeasts, such as [[baker's yeast]] and ''[[Candida (genus)|Candida]]'' which are in general single-celled, or short chains of cells, and reproduce vegetatively by budding rather than by the production of hyphae. As a result, most were classified in a vaguely defined taxon with the older name '''Hemiascomycetes'''. *The subphylum '''[[Taphrinomycotina]]''' includes a disparate group of Ascomycota and were only recognized as a distinctive group after the advent of molecular ([[DNA]]) analyses. The group is basal to the other subphyla and hence is considered to be more primitive. Consequently the taxon was originally named '''[[Archiascomycetes]]''' alternatively spelled '''[[Archaeascomycetes]]'''. It includes both hyphal fungi (''[[Neolecta]]'', ''[[Taphrina]]''), and fission yeasts ''[[Schizosaccharomyces]]'' and the peculiar mammalian lung parasite, ''[[Pneumocystis]]'' that was originally believed to be a [[protozoan]]. == Commonly used but obsolete morphologically defined class names == Several obsolete class names, based upon morphology, are still used in informal or introductory discussions. Among those based upon the sexual [[fruit body|fruitbodies]] ([[teleomorph]]s) are: the '''[[Discomycetes]]''' which included all species forming '''[[apothecia]]'''; the '''[[Pyrenomycetes]]''' which included all sac fungi that formed '''[[perithecia]]''' or even [[ascocarp|pseudothecia]], or any structure approaching these morphological structures; and the '''[[Plectomycetes]]''' which included those Ascomycota that formed '''[[ascocarp|cleistothecia]]'''. '''[[Hemiascomycetes]]''' included the yeasts and yeast-like fungi that are now split between [[Saccharomycotina]] and [[Taphrinomycotina]], while the '''[[Euascomycetes]]''' covered the rest of the Ascomycota, now in the '''[[Pezizomycotina]]''' and ''[[Neolecta]]'' in the Taphrinomycotina. Some Ascomycota never reproduce sexually, or are not known to produce [[ascus|asci]]. These are sometimes called "[[Mitosporic Ascomycota]]" because of the production of conidia otherwise known as mitospores, and other asexual structures, all collectively called [[anamorph]]ic taxa. In some classifications these would have been placed in a separate artificial phylum, the '''[[Deuteromycota]]''' (also known as '''[[Fungi Imperfecti]]'''). Molecular analyses can now be used to place these genera and species among ascus-bearing taxa (if they are Ascomycota), or amongst other phyla such as the [[Basidiomycota]] (if related to them). No mitosporic taxa have been found that form a phylum distinct from the other major phyla of Fungi. [[Anamorph]]s are discussed below. However, it is extremely difficult in the absence of molecular analysis to link most anamorphic (asexual morphs) fungi to their teleomorphs (sexual counterparts). There are over 250 years of names available (since [[Linnaeus]]' [[Species Plantarum]], 1753) for both asexual and sexual components of the same fungi. For instance the sexual form of the [[kerosene fungus]] is known as ''[[Amorphotheca]] resinae'' while the asexual stage is called ''[[Hormoconis]] resinae''. Most anamorphic fungi are Ascomycota, and therefore the obsolete classification of the Deuteromycota is largely that of Ascomycota anamorphs. The Deuteromycota were classified as '''[[Coelomycetes]]''' if they produced their conidia in small seed-like, fly-speck sized, flask-shaped [[conidia|conidiomata]], or structures resembling or approximating them in structure. The '''[[Hyphomycetes]]''' were those species where the conidiophores (i.e. the hyphae which carry conidia-forming cells on the end) are free or loosely organized. They are mostly isolated but sometimes also appear as bundles of cells aligned in parallel (described as ''synnematal'') or as cushion-shaped masses (described as ''sporodochial''). == Physical make-up == The adjective which describes these fungi is "ascomycetous". The majority of ascomycetous fungi grow as a [[thallus]], called a [[mycelium]], consisting of many [[hyphae]] which are microscopic multi-branched filaments. If the hyphae of some typical mycelia were laid end to end, they could reach a length of several kilometers. Ascomycota typically produce great numbers of [[ascus|asci]] at any one time, and these may be contained in a multicellular, often readily visible structure called an "[[ascocarp]]" (also called an "ascoma", the [[fruiting body]] of ascomycetes). Many exceptions to the structure described above occur, for example in one extreme these fungi are single celled yeasts, and there is no mycelium, no fruitbody, and the entire cell is converted into an ascus in such ascomycetous [[yeast]]s such as baker's Yeast (''[[Saccharomyces cerevisiae]]''). In the case of [[lichen]]ized species, the thallus of the fungus defines the shape of the [[symbiosis|symbiotic]] colony. Other Ascomycota are [[Phenotypic switching|dimorphic]], which can mean that they can appear either in single- or multi-cellular form. Other species are [[pleomorphic]], exhibiting multiple asexual forms (i.e. [[anamorph]]s detailed below) as well as a sexual form (a [[teleomorph]]). The [[ascoma]] come in multiple forms: 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, solitary or clustered, etc. They can be fleshy or carbonaceous (like charcoal), leathery, rubbery, gelatinous, slimy, powdery, or cob-web-like, etc. They come in multiple colors such as red, orange, yellow, and rarely green or blue, although brown or black are more common. Except for lichens, the mycelium (if produced) is usually inconspicuous because it is subterranean or embedded in the substrate, and only the ascoma is seen in season. But spectacular, bizarre, or otherwise noteworthy exceptions occur. Many ascomatous fungi have [[melanin|melanized]] hyphal walls (referred to as dematiaceous walls) and therefore are black or brown. Black spots on bathroom caulking are often colonies of Ascomycota, e.g. ''[[Cladosporium]]''. Many [[mold]]s that grow on spoiled foods are Ascomycota, and therefore the pellicles or skins that develop on jams, juices, and other foods in containers at home are in fact the thalli of Ascomycota (occasionally [[Mucoromycotina]], and almost never [[Basidiomycota]]). [[Sooty molds]] that develop on plants, especially in the tropics are the thalli of many species. Sometimes it is the mass of asci or ascus-like cells, or conidia or yeast cells that are the conspicuous elements. [[Pneumocystis]] species fill lung cavities causing a form of pneumonia (visible in x-rays). [[Ascosphaera]] cysts ([[ascus|asci]]) fill [[honey bee]] [[larva]]e and [[pupae]] making them appear mummified and chalk-like, hence the name "chalkbrood". Free living yeasts form yeast colonies. Excessive ''[[Candida (genus)|Candida]]'' yeast growth in the mouth or vagina is called "thrush" or [[candidiasis]]. The cell walls of these fungi are almost always formed of [[Chitin]] and β-Glucans; individual cells are formed from divisions of the hyphae called "[[septum|septa]]". These give stability to the hyphae and prevent a great loss of [[cytoplasm]] in the event that the [[cell membrane]] should be locally damaged. Mostly the cell divisions are centrally perforated, so they have a small opening in the middle, through which cytoplasm and also [[Cell nucleus|nuclei]] can move more or less freely throughout the system of hyphae. Often hyphae have only one nucleus per cell, and are therefore described as ''uninucleate'', but some ascomycetous fungi can also be [[multinucleate]] at times. [[Image:Smardz-Morchella-Ejdzej-2006.jpg|thumb|right|179px|The ascocarp of a [[morel]] contains numerous apothecia.]] == Metabolism == Like most fungi the Ascomycota principally digest living or dead biomass. To achieve this, they secrete into their surroundings powerful [[digestive enzymes]] which break down organic substances into small molecules, which are then absorbed through the cell wall. Many species live on dead plant material such as fallen leaves, twigs, or logs. Others attack plants, animals, or other fungi as [[parasite]]s and derive their metabolic energy, as well as all the nutrients they need, from the cell tissue of their hosts. Especially in this group extreme specialization appears; for instance certain [[species]] of [[Laboulbeniales]] attack only one particular leg of one particular insect species. The Ascomycota also often take up symbiotic relationships – for instance some combine with green [[alga]]e or [[cyanobacteria]], from which they obtain photosynthetic nutrients, to form [[lichen]]s; others form [[symbiosis|symbioses]] with tree roots as [[mycorrhiza]]l fungi. There are also carnivorous fungi, which have developed hyphal traps in which they can catch small [[protist]]s such as [[amoeba]]e, as well as [[roundworm]]s (''Nematoda''), [[rotifer]]s, [[tardigrade]]s, and small arthropods such as [[springtail]]s (''Collembola''). Through their long evolutionary history the Ascomycota have developed the capability to break down almost every organic substance. Unlike most organisms they are able to use their own [[enzyme]]s to digest plant [[cellulose]] and the [[lignin]] contained in wood. [[Collagen]], an abundant structural protein in animals, and [[keratin]] (which hair is made of), can also serve as food sources. Exotic examples are given by the ascomycete ''Aureobasidium pullulans'', which metabolizes wall paint, and the kerosene fungus ''Amorphotheca resinae'', which (to the misfortune of the airline industry) feeds on aircraft fuel, and in tropical regions sometimes blocks fuel pipes. Others resist [[osmotic pressure|osmotic stress]] to grow on salted fish, and a few live in water. [[Image:Hypomyces completus.jpg|thumb|left|250px|''Hypomyces completus'' on culture medium]] == Distribution and living environment == The Ascomycota are present in all land ecosystems world-wide – they even occur in [[Antarctica]] – and their spores and hyphal fragments are distributed through the atmosphere and fresh water environments, as well as ocean beaches and tidal zones. The distribution of individual species is very variable: some are found on all continents, while for example the [[Tuber (genus)|white truffle]] ''Tuber magnatum'', which is much sought after for culinary purposes, only appears in isolated locations in Italy and France. Plant parasitic species are often restricted by their host distributions. ''[[Cyttaria]]'' is only found on ''[[Nothofagus]]'' ([[Southern Beech]]) in the [[Southern Hemisphere]]. == Reproduction == === Asexual reproduction === Asexual reproduction is the dominant form of propagation in the Ascomycota, and is responsible for the rapid expansion of these fungi into areas which were previously not colonized. It occurs through reproductive structures, the "[[conidium|conidia]]," which are genetically identical to the parent and mostly have just one nucleus. They are also called "mitospores" due to the way they are generated through the cellular process of [[mitosis]]. They are generally formed on the ends of specialized [[hypha]]e, the "conidiophores". Depending on the species they may be dispersed by wind or water, or also by animals. ==== Asexual spores ==== In order to further classify the Ascomycota in the asexual stages, it is important to consider the spores, which can be distinguished by colour, form and the way they are separated into cells. The most frequent types are the single-celled spores which are designated ''amerospores''. If the spore is divided into two by a cross-wall ([[septum]]), it is a ''didymospore''. {| align="right" cellspacing="0" cellpadding="0" |[[Image:Trichoderma aggressivum.jpeg|thumb|right|250px|Conidiospores of ''Trichoderma aggressivum'', Diameter approx. 3µm]] |- |[[Image:Aspergillus.jpg|thumb|right|250px|Conidiophores of molds of the genus ''Aspergillus'', conidiogenesis is blastic-phialidic]] |- |[[Image:Trichoderma harzianum.jpg|thumb|right|200px|Conidiophores of ''[[Trichoderma harzianum]]'', conidiogenesis is blastic-phialidic]] |- |[[Image:Trichoderma fertile.jpg|thumb|right|200px|Conidiophores of ''Trichoderma fertile'' with vase-shaped phialides and newly formed conidia on their ends (bright points)]] |} When there are two or more cross-walls the classification depends on the shape. If the septa are ''transversal'', like the rungs of a ladder, it is a ''phragmospore'' whilst if they form a net-like structure it is a ''dictyospore''. In ''staurospores'' ray-like "arms" radiate from a central body; in others (''helicospores'') the entire spore is wound up in a spiral like a spring. Finally very long worm-like spores, of which the ratio length:diameter is more than 15:1, are called ''scolecospores''. ==== Conidiogenesis and dehiscence ==== One distinguishes: *acervular conidiomata, or ''acervuli'', which develop in the host and can thus be: *#''subcuticular'', lying under the outer layer of the plant (the [[Plant cuticle|cuticle]]), *#''intraepidermal'', inside the outer cell layer (the [[Epidermis (botany)|epidermis]]), *#''subepidermal'', under the epidermis, or *#deeper inside the host. :Mostly they develop a flat layer of relatively short conidiophores which then produce masses of spores. The increasing pressure finally leads to the splitting of the epidermis and cuticle and so allows the conidia to escape. *pycnidial conidiomata or '''pycnidia''', which unlike the acervuli form in the fungal tissue itself, and which are generally shaped like a bulging vase. The spores are released through a small opening at the apex, the '''ostiole'''. Two further important characteristics of the anamorphs of the Ascomycota are the ''conidiogenesis'', the fashion in which the spores are formed, and their ''dehiscence'', i.e. how they separate from the parent structures. The former corresponds to [[Embryology]] in animals and plants and can be divided into two fundamental forms of development: ''blastic'' conidiogenesis, where the spore is already evident before it separates from the conidiogenic hypha which is giving rise to it, and ''thallic'' conidiogenesis, where first a cross-wall appears and then the thus created cell develops into a spore. 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 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 which is concentrically inside the scar left by the previous spore), *'''blastic-phialidic''' (the spores arise and are ejected from the open ends of special conidiogenic cells called [[phialide]]s which remain constant in length; an example is the anamorph of ''Penicillium''), *'''basauxic''' (where a chain of conidia, in successively younger stages of development, is emitted from the mother cell), *'''blastic-retrogressive''' (spores separate off 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 which develop into short, cylindrical spores called '''arthroconidia'''; 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 a ''phragmospore''). Essentially dehiscence can happen in two different ways. In the '''schizolytic''' variant a double dividing wall with a central lamella (layer) forms ''between'' the cells; the central layer dissolves to release the spores. In the case of '''rhexolytic''' dehiscence on the other hand the cell wall which joins the spores on the ''outside'' simply degenerates and sets free the conidia. === Heterocaryosis and parasexuality === A significant number of Ascomycota species either have no sexual stage or none is known. In spite of this, there are two ways in which they can conserve their genetic diversity: '''Heterocaryosis''' and '''Parasexuality'''. The former happens simply through the merging of two hyphae belonging to different individuals, a process known as '''anastomosis'''. As a result there are more [[Cell nucleus|cell nuclei]] than normal in the [[mycelium]] and they come from genetically different parent organisms. '''Parasexuality''', on the other hand, refers to a phenomenon where two cell nuclei merge without any sexual process and the [[chromosome]] count is doubled. This involves a complex form of the type of cell division called [[mitosis]], where there is ''crossing over'' or ''[[genetic recombination|recombination]]'', i.e. an exchange of genetic material between corresponding pairs of chromosomes. In sexual reproduction, in contrast, crossing over occurs only during [[meiosis]]. Finally the chromosome count will be restored to normal by [[haploidization]], whereby the nucleus splits into two parts each having a single set of chromosomes, with each daughter genetically different from the original parents. === Sexual reproduction === [[Image:Hypocrea virens.jpg|thumb|right|115px|Ascus of ''Hypocrea virens'' with eight two-celled Ascospores]] Sexual reproduction in the Ascomycota is marked by a characteristic structure, the ''ascus'', which distinguishes these fungi from all others. An ascus is a tube-shaped vessel, a ''meiosporangium'', which contains the sexual spores produced by [[meiosis]]. The latter are called ''ascospores'' in contrast to the asexual ''conidiospores''. Apart from exceptions such as baker's Yeast ([[Saccharomyces cerevisiae]]), almost all fungi of the Ascomycota are [[haploid]], so their nuclei only contain one set of [[chromosome]]s, which makes them especially susceptible to mutations. During sexual reproduction there is a [[diploid]] phase (with two sets of chromosomes), which as a rule is very short. Then meiosis occurs, generally very soon, so that the haploid state is re-established. ==== The formation of sexual spores ==== The sexual part of the life cycle commences when two suitable hyphae meet each other. These come from the same web of hyphae which can also generate asexual spores. The first deciding factor as to whether conjugation - that is, sexual merging - will occur, is whether the hyphae belong to the same organism, or whether they come from different individual fungi. Whilst many species are thoroughly capable of self-propagation, i.e. they are '''homothallic''', others need non-identical partners and so are '''heterothallic'''. Besides this, the two hyphae in question must also belong to the same [[mating type]]. Mating types are a peculiarity of the fungi and correspond roughly to the sexes in plants and animals; however one species may have more than two mating types. In the case of compatibility, '''gametangia''' form on the hyphae; these are the generative cells for the [[gamete]]s, in which numerous nuclei gather. A very fine hypha, called the '''trichogyne''', which grows out of one gametangium, now termed the '''ascogonium''', makes a passage to a gametangium of the other individual, which is then the '''antheridium'''. Nuclei then pass from the antheridium (playing a 'male' role) to the ascogonium (playing a 'female' role). Unlike the process in animals and plants, after the union of the [[cytoplasm]]s of the two gametangia ('''plasmogamy'''), the merging of the nuclei ('''karyogamy''') does not usually occur immediately. Instead, the nuclei which have migrated in from the antheridium pair up with the nuclei of the ascogonium, but remain separate next to their partners. With this the '''dikaryophase''' of the life cycle begins; during this time the pairs of nuclei repeatedly synchronously divide, so that a great number are produced. In all probability the dikaryophase is an evolutionary adaptation which serves to exploit the potential of sexual reproduction to the full in circumstances where it is a rare event for different individuals to meet each other. After the genetic raw material has been increased by repeated division, [[genetic recombination|recombination]] will take place independently in each pair during [[meiosis]], so that the greatest possible quantity of genetically different spores will arise. In the [[red alga]]e (Rhodophyta) a similar solution to the corresponding problem evolved independently. Next millions of new '''dinucleate''' hyphae, into each of which two nuclei migrate, emerge from the fertilized ascogonium. They are also called '''ascogenous''' or ''fertile''. They are fed by ordinary '''uni-''' or '''mononucleate''' hyphae (with only one nucleus), which are also called ''sterile''. The tissue of sterile and fertile hyphae now grows in many cases into a macroscopically visible fruiting body, the '''[[ascocarp]]''', which may contain millions of fertile hyphae. [[Image:Hypomyces chrysospermus.jpg|thumb|left|150px|Unitunicate-inoperculate Asci of ''Hypomyces chrysospermus'']] In the actual fruiting layer, the [[hymenium]], the '''[[ascus|asci]]''' now appear. At one end of an ascogenous hypha, there develops a U-shaped hook, which points back opposite to the general growth direction. The two nuclei contained in the terminal cell then divide in such a way that the threads of their [[mitotic spindle]]s run parallel, and thus two pairs of genetically different daughter nuclei arise, with one daughter of each pair near the point of the hook, and the other in the base part of the hypha. Then two parallel cross-walls appear, dividing the hypha into three sections: that at the point of the hook with one nucleus, that at the base of the original hypha with one nucleus, and the middle U-shaped part with two nuclei. If the positioning in the fruiting layer is right, the karyogamic fusion of the nuclei finally takes place in the U-shaped cell, creating the diploid [[zygote]]. It lengthens to form an elongated tube-shaped or cylinder-shaped capsule, the actual '''ascus'''. Then [[meiosis]] occurs, giving rise to four [[haploid]] nuclei. This is almost always followed by a further [[mitotic]] division, so that the ascus ultimately has eight daughter nuclei. These become enclosed, together with some of the cell plasma, each by their own membranes, and generally with a hard cell wall. Thus the dissemination cells (the '''ascospores''') develop, lying initially like peas in a pod inside the ascus. Later, when an appropriate opportunity presents itself, they are liberated. Not having [[flagellum|flagella]], ascospores are disseminated in various other ways: some are spread by wind and with others the ripe ascus breaks open on contact with water to set free the spores. Certain species have evolved regular 'spore cannons' which can eject them up to 30 cm. away. When the spores reach a suitable substrate, they germinate, form new hyphae, and so restart their life cycle, which has come full circle. 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 on [[Ascus|asci]] for further details. == Ecology == The Ascomycota fulfil a central role in most land-based [[ecosystem]]s. They are important [[decomposer]]s which break down such organic materials as dead leaves, twigs, fallen trees, etc. and help the [[detritivore]]s (animals which live off this decomposing material) to obtain their nutrients. By processing substances like [[cellulose]] or [[lignin]], which are otherwise difficult to exploit, they take on an important place in the natural [[nitrogen cycle]] and the [[carbon cycle]]. Inversely the fruiting bodies of the Ascomycota provide food for a very diverse set of animals from [[insect]]s and slugs and snails (''[[Gastropoda]]'') to [[rodent]]s and larger mammals such as [[deer]] and [[wild boar]]s. Fungi of the Ascomycota are also known for their numerous [[symbiotic]] relationships with other organisms. === Lichens === {| align="right" |[[Image:Pseudevernia-furfuracea-Schnitt.jpg|thumb|250px|Cross-section through the lichen ''Pseudevernia furfuracea'' with plainly visible layer of green algae under the surface]] |- |[[Image:Pseudevernia furfuracea02.jpg|thumb|250px|''Pseudevernia furfuracea'']] |} Probably since early in their evolutionary history the Ascomycota have "domesticated" [[green algae]] (''Chlorophyta''), as well as occasionally other types of [[alga]]e and [[cyanobacteria]]. Together they form the mutualistic associations known as '''[[lichens]]''', which can survive in the least hospitable regions of the earth, including the [[Arctic]], the [[Antarctic]], [[desert]]s and mountaintops, and can withstand temperature extremes from -40°C to +80°C. While the [[photoautotroph]]ic algal partner creates metabolic energy through photosynthesis, the fungus offers a stable supportive framework and protects from radiation and drying out. Around 42% of the Ascomycota (numerically about 18,000 species) form lichens, and almost all the fungal partners of lichens belong to the Ascomycota - the proportion of Basidiomycota is probably only two to three percent. === Mycorrhizal fungi and endophytes === Members of the Ascomycota make two particularly important types of relationship with plants: as '''[[mycorrhiza]]l''' fungi and as '''[[endophyte]]s'''. The former make [[symbiotic]] associations with the root systems of the plants, which for some trees, especially conifers, can be of vital importance, enabling the uptake of mineral salts from the soil. The fungal partner is in a much better position to absorb minerals due to its finely divided mycelium, whilst the plant provides it with metabolic energy in the form of [[photosynthetic]] products. Cases are even known where mycorrhizal fungi can transport nutrients from one plant to another, stabilizing the recipient. It is likely that mycorrhizal associations enabled the conquest of the land by plants - in any case the earliest known fossils of land plants have mycorrhizae. '''[[Endophyte]]s''' on the other hand live inside plants, especially in the stem and leaves, but generally do not damage their hosts. The exact nature of the relationship between endophytic fungus and host is not yet well understood, but it seems that this form of colonization can bestow a higher resistance against insects, [[roundworm]]s (nematodes), and [[bacteria]]; also it can enable or augment the production of poisonous [[alkaloid]]s, chemicals which can affect the health of plant-eating mammals. === Symbiotic relationships with animals === A series of Ascomycota species from the genus ''Xylaria'' are found in the nests of [[leafcutter ant]]s and other [[fungus-growing ants]] of the tribe ''Attini'' and in the fungal gardens of [[termite]]s (''Isoptera''). Since they do not generate fruiting bodies until the insects have left the nests, it is suspected that, as confirmed in several cases of [[Basidiomycota]] species, they may be cultivated. On the other hand [[bark beetle]]s (''Scolytidae'') are certainly important symbiotic partners. The female beetles transport the spores to new hosts in characteristic tucks in their skin, the ''mycetangia''. There they eat tunnels in the wood, which lead into large chambers in which they lay their eggs. At this time the spores are released and give rise to hyphae which unlike the beetles can digest the wood. The beetle larvae feed on the fungus and after they have metamorphosed into the adult state they again carry spores with them to renew the cycle of infection. A well-known example of this is [[Dutch elm disease]], caused by fungus ''Ophiostoma ulmi'', being carried by the European elm bark beetle ''Scolytus multistriatus''. == Importance for humans == [[Image:Ophiostoma minus.jpeg|thumb|left|250px|Tree attacked by the Bluestain fungus, ''Ophiostoma minus'']] Ascomycetes make many contributions to the good of humanity, and also have many ill effects. === Harmful 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 species ''Ophiostoma ulmi'' and ''Ophiostoma novo-ulmi'', has led to the death of many elms in Europe and North America. [[Image:Rogge moederkoren Claviceps purpurea on Secale cereale.jpg|thumb|right|180px|''Claviceps purpurea'' on rye (''Secale cereale'')]] *The originally Asian [[chestnut blight|''Cryphonectria parasitica'']] is responsible for attacking [[Sweet Chestnut]]s (''Castanea sativa''), and virtually eliminated the once-widespread [[American Chestnut]] (''Castanea dentata''), *A disease of [[Maize]] (''Zea mays''), which is especially prevalent in North America, is brought about by ''Cochliobolus heterostrophus''. *''Taphrina deformans'' causes [[leaf curl]] of peach. *''[[Uncinula necator]]'' is responsible for the disease [[Powdery mildew]], which attacks grapevines. *Species of ''Monilia'' cause brown rot of stone fruit such as peaches (''Prunus persica'') and sour cherries (''Prunus ceranus''). *Members of the Ascomycota such as ''[[Stachybotrys chartarum]]'' are responsible for fading of woollen textiles, which is a great problem especially in the tropics. *Blue-green, red and brown [[mould]]s attack and spoil foodstuffs - for instance ''[[Penicillium]] italicum'' rots oranges. *Cereals infected with ''[[Fusarium]] graminearum'' contain [[mycotoxin]]s like [[deoxynivalenol]] (DON), which can lead to skin and mucous membrane lesions when eaten by pigs. *[[Ergot]] (''Claviceps purpurea'') is a direct menace to humans when it attacks wheat or rye and produces highly poisonous and [[carcinogenic]] [[alkaloid]]s, causing [[ergotism]] if consumed. Symptoms include hallucinations, stomach cramp, and a burning sensation in the limbs ("Saint Anthony's Fire"). *''[[Aspergillus flavus]]'', which grows on peanuts and other hosts, generates [[aflatoxin]], which damages the liver and is highly carcinogenic. *''[[Candida albicans]]'', a yeast which attacks the mucous membranes, can cause an infection of the mouth or vagina called thrush or [[candidiasis]], and is also blamed for "yeast allergies". *Fungi like ''[[Epidermophyton]]'' cause 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 jiroveci'' is responsible for severe lung infections which occur in [[AIDS]] patients. === Positive effects === On the other hand, ascus fungi have brought some important benefits to humanity. *The most famous case may be that of the mould ''Penicillium chrysogenum'' (formerly ''[[Penicillium notatum]]''), which, probably to attack competing bacteria, produces an antibiotic which, under the name of [[Penicillin]], triggered a revolution in the treatment of bacterial infectious diseases in the 20th century. *The medical importance of ''Tolypocladium niveum'' as an [[immunosuppression|immunosuppressor]] can hardly be exaggerated. It excretes [[Ciclosporin]], which, as well as being given during [[organ transplant]]s to prevent rejection, is also prescribed for auto-immune diseases such as [[multiple sclerosis]], although there is some doubt over the long-term side-effects of the treatment. [[Image:Blue Stilton Quarter Front.jpg|thumb|right|180px|Stilton cheese veined with ''Penicillium roqueforti'']] *Some ascomycete fungi can be altered relatively easily through [[genetic engineering]] procedures. They can then produce useful proteins such as [[insulin]], [[human growth hormone]], or TPa, which is employed to dissolve blood clots. *The red bread mould ''[[Neurospora crassa]]'' is an important [[model organism]] in biology, of which the [[genome]] has now been fully sequenced. *Baker's Yeast (''[[Saccharomyces cerevisiae]]'') is used to make [[bread]], [[beer]] and [[wine]], during which process sugars such as [[glucose]] or [[sucrose]] are fermented to make [[alcohol]] and [[carbon dioxide]]. In the case of bread-making, the alcohol evaporates and the carbon dioxide serves to make the dough rise. *Enzymes of ''[[Penicillium camemberti]]'' play a role in the manufacture of the cheeses [[Camembert (cheese)|Camembert]] and [[Brie (cheese)|Brie]], while those of ''[[Penicillium roqueforti]]'' do the same for [[Gorgonzola (cheese)|Gorgonzola]], [[Roquefort]] and [[Stilton (cheese)|Stilton]]. *In Asia ''[[Aspergillus oryzae]]'' is added to a pulp of soaked soya beans to make [[soy sauce]]. *Finally, some members of the Ascomycota are eaten with relish; [[morel]]s (''Morchella'') and [[Tuber (genus)|truffle]]s (''Tuber'') are some of the most sought-after fungus delicacies. == Notes == # {{Note_label<!--1-->|Taylor_1996|1|a}} {{Harv|Taylor|Spatafora|Berbee|1996}} and reference 4. # {{Note_label<!--2-->||2|b}} The taxonomic system used here (based on reference 1) is only one among several; another authoritative one is given by references 2 & 3. # {{Note_label<!--4-->||4|d}} See reference 5. == Linked references == * All but the first 2 sections are translated from the [[:de:Ascomycota|German article]]. {{Reflist|2}} == Unlinked references == {{wikispecies|Ascomycota}} # {{Harvard reference | Surname1=Taylor | First1=John W. | Surname2=Spatafora | First2=Joey | Surname3=Berbee | First3=Mary | Year=1996 | Title=Ascomycota | Periodical=Tree of Life |date=[[March 11]], [[1996]] | URL=http://tolweb.org/Ascomycota }}. # ''Ainsworth and Bisby's Dictionary of the Fungi'', 9th Edition, see [http://www.cabi-publishing.org/bookshop/BookDisplay.asp?SubjectArea=&Subject=&PID=1529 here] for more details. # See the [http://www.indexfungorum.org/Names/Fundic.asp Index Fungorum (Hierarchy Search)] for a web search based on the previous reference. # [http://www.fieldmuseum.org/myconet/printed_v7.asp Outline of Ascomycota - 2001] <!--# [http://www.umu.se/myconet/M7.html Outline of Ascomycota - 2001], which is part of [http://www.umu.se/myconet/Myconet.html MYCONET]. --> # [http://www.palaeos.com/Fungi/Ascomycota/Ascomycota.html Palæos Fungi] # C. J. Alexopoulos, M. Blackwell, C. W. Mims: ''Introductory Mycology'', 4th Ed., 1996, ISBN 0-471-52229-5 # B. Kendrick: "The Fifth Kingdom, 3rd Ed., 2001, Kapitel 4, ISBN 1-58510-022-6 # G. J. Krieglsteiner: ''Verbreitungsatlas der Großpilze Deutschlands (West)'', Volume 2: Schlauchpilze, Ulmer Verlag, 1993 # F. Breitenbach, J. Kränzlin: ''Pilze der Schweiz'', Volume 1, Ascomycetes, Mykologia Luzern, 1984 #[http://www.cbs.knaw.nl/databases/index.htm Anamorph-Teleomorph-Datenbank] <!-- #[http://www.umu.se/myconet/M7.html Klassifikation aller gültigen Gattungen und höheren Taxa der Schlauchpilze] --> #[http://www.pilzfotopage.de/Ascomyceten/pages/indexAleuria%20aurantia.html Fotografien einiger Fruchtkörper (Ascomata)] [[Category:Fungi]] [[Category:Ascomycota| ]] [[Category:pages needing expert attention]] {{Link FA|de}} [[an:Ascomycota]] [[cs:Houby vřeckovýtrusné]] [[da:Sæksvampe]] [[de:Schlauchpilze]] [[es:Ascomycota]] [[eo:Askofungoj]] [[eu:Ascomycota]] [[fr:Ascomycota]] [[is:Asksveppir]] [[it:Ascomycota]] [[lv:Asku sēnes]] [[lt:Aukšliagrybūnai]] [[hu:Tömlősgombák]] [[mk:Торбести габи]] [[nl:Ascomyceten]] [[ja:子嚢菌門]] [[no:Sekksporesopper]] [[pl:Workowce]] [[pt:Ascomycota]] [[ro:Ascomycota]] [[ru:Аскомицеты]] [[sk:Vreckaté huby]] [[sv:Sporsäcksvampar]] [[tr:Asklı mantarlar]] [[uk:Аскоміцети]] [[wa:Ascomicete]] [[zh:子囊菌门]]