Epichloë ist eine Pilzgattung aus der Familie der Mutterkornpilzverwandten (Clavicipitaceae). Sie sind Symbionten, die endophytisch in verschiedenen Süßgräsern aus der Unterfamilie Pooideae leben und zum Fraßschutz der Wirtspflanze beitragen. Die Typusart der Gattung Epichloë ist der Gras-Kernpilz (Epichloë typhina). Die sich asexuell fortpflanzenden Verwandten von Epichloë werden in der anamorphen Gattung Neotyphodium zusammengefasst.
Die Vertreter der Gattung Epichloë sind endophytische Pilze, die in den Interzellularräumen der Blätter und Stängel ihrer Wirtspflanzen leben und mit diesen eine konstitutiv-symbiotische Lebensgemeinschaft bilden. Die Wirtspflanze versorgt den Pilz mit Nährstoffen. Darüber hinaus kontrolliert die Wirtspflanze das Wachstum des Pilzes.[1] Der Pilz schützt im Gegenzug die Wirtspflanze durch seine Produktion von Alkaloiden vor Fraßfeinden wie Insekten, pflanzenfressenden Wirbeltieren und Wurzelgallennematoden. Ebenso verbessert der Pilz die Widerstandskraft der Wirtspflanze gegen Trockenheit und kontrolliert deren Wurzelwachstum und die Fruchtreifung.[2]
Vertreter der Gattung Epichloë können mehrere verschiedene Alkaloide produzieren, wozu auch Mutterkornalkaloide gehören, insbesondere Ergovalin und verschiedene Clavine.
Des Weiteren können sie Lolitreme und Lolinalkaloide (Loline) – wie das aus Taumel-Lolch (Lolium temulentum) isolierte Temulin (Norlolin) – sowie das Guanidiniumalkaloid Peramin bilden. Während Peramin und Loline als Insektizid wirken, haben Lolitreme eine neurotoxische Wirkung auf Wirbeltiere, was sich an Zittern (Tremor) zeigen kann. Von dieser Wirkung kann insbesondere Weidevieh betroffen werden, wenn es Gras konsumiert, beispielsweise Lolium perenne (Ausdauernder Lolch), das mit Epichloë infiziert ist. Eine ebenfalls vorwiegend auf Wirbeltiere toxische Wirkung haben die von Epichloë-Arten gebildeten verschiedenen Mutterkornalkaloide. Zu den durch diese hervorgerufenen Symptomen bei Weidevieh werden Gewichtsverlust, Durchblutungsstörungen sowie Störungen der Fortpflanzungsfähigkeit und Laktation gezählt.[3]
Sporen und Teile des Mycels kommen auch in den Samen der Wirtspflanzen vor. Auf diese Weise bildet sich die Lebensgemeinschaft aus Pilz und Wirtspflanze bereits während der Keimlingsentwicklung.
Die Gattung Epichloë gehört innerhalb der Familie der Mutterkornpilzverwandten zum Tribus Balansieae, zu dem unter anderem auch die endo- und epiphytisch auf verschiedenen Süßgräsern lebenden Gattungen Atkinsonella, Balansia und Myriogenospora zählen.
Mit der Gattung Epichloë sehr nahe verwandt ist die Gattung Neotyphodium. Das wesentliche Unterscheidungsmerkmal ist das Fehlen des sexuellen Zyklus in der Gattung Neotyphodium. Neotyphodium-Arten stammen entwicklungsgeschichtlich von Vertretern der Gattung Epichloë ab, wobei Hybridisierungsprozesse eine wichtige Rolle gespielt haben.[4][5]
Epichloë ist eine Pilzgattung aus der Familie der Mutterkornpilzverwandten (Clavicipitaceae). Sie sind Symbionten, die endophytisch in verschiedenen Süßgräsern aus der Unterfamilie Pooideae leben und zum Fraßschutz der Wirtspflanze beitragen. Die Typusart der Gattung Epichloë ist der Gras-Kernpilz (Epichloë typhina). Die sich asexuell fortpflanzenden Verwandten von Epichloë werden in der anamorphen Gattung Neotyphodium zusammengefasst.
Epichloë is a genus of ascomycete fungi forming an endophytic symbiosis with grasses. Grass choke disease is a symptom in grasses induced by some Epichloë species, which form spore-bearing mats (stromata) on tillers and suppress the development of their host plant's inflorescence. For most of their life cycle however, Epichloë grow in the intercellular space of stems, leaves, inflorescences, and seeds of the grass plant without incurring symptoms of disease. In fact, they provide several benefits to their host, including the production of different herbivore-deterring alkaloids, increased stress resistance, and growth promotion.
Within the family Clavicipitaceae, Epichloë is embedded in a group of endophytic and plant pathogenic fungi, whose common ancestor probably derived from an animal pathogen. The genus includes both species with a sexually reproducing (teleomorphic) stage and asexual, anamorphic species. The latter were previously placed in the form genus Neotyphodium but included in Epichloë after molecular phylogenetics had shown asexual and sexual species to be intermingled in a single clade. Hybrid speciation has played an important role in the evolution of the genus.
Epichloë species are ecologically significant through their effects on host plants. Their presence has been shown to alter the composition of plant communities and food webs. Grass varieties, especially of tall fescue and ryegrass, with symbiotic Epichloë endophyte strains, are commercialised and used for pasture and turf.
Elias Fries, in 1849, first defined Epichloë as a subgenus of Cordyceps.[2] As type species, he designated Cordyceps typhina,[2] originally described by Christiaan Hendrik Persoon.[3] The brothers Charles and Louis René Tulasne then raised the subgenus to genus rank in 1865.[4] Epichloë typhina would remain the only species in the genus until the discovery of fungal grass endophytes causing livestock intoxications in the 1970s and 1980s, which stimulated the description of new species.[5] Several species from Africa and Asia that develop stromata on grasses were split off as a separate genus Parepichloë in 1998.[6]
Many Epichloë species have forms that reproduce sexually, and several purely asexual species are closely related to them. These anamorphs were long classified separately: Morgan-Jones and Gams (1982) collected them in a section (Albo-lanosa) of genus Acremonium.[7] In a molecular phylogenetic study in 1996, Glenn and colleagues found the genus to be polyphyletic and proposed a new genus Neotyphodium for the anamorphic species related to Epichloë.[8] A number of species continued to be described in both genera until Leuchtmann and colleagues (2014) included most of the form genus Neotyphodium in Epichloë.[5] Phylogenetic studies had shown both genera to be intermingled, and the nomenclatural code required since 2011 that one single name be used for all stages of development of a fungal species. Only Neotyphodium starrii, of unclear status, and N. chilense, which is unrelated, were excluded from Epichloë.[5]
As of 2022, there are 37 accepted species in the genus, with 3 subspecies and 6 varieties described. 15 species, 3 subspecies and 5 varieties are haploid. 22 species and 1 variety are hybrids (allopolyploids). Several taxa are only known as anamorphic (asexual) forms, most of which have previously been classified in Neotyphodium.[5]
Epichloë species are specialized to form and maintain systemic, constitutive (long-term) symbioses with plants, often with limited or no disease incurred on the host.[9] The best-studied of these symbionts are associated with the grasses and sedges, in which they infect the leaves and other aerial tissues by growing between the plant cells (endophytic growth) or on the surface above or beneath the cuticle (epiphytic growth). An individual infected plant will generally bear only a single genetic individual clavicipitaceous symbiont, so the plant-fungus system constitutes a genetic unit called a symbiotum (pl. symbiota).
Symptoms and signs of the fungal infection, if manifested at all, only occur on a specific tissue or site of the host tiller, where the fungal stroma or sclerotium emerges. The stroma (pl. stromata) is a mycelial cushion that gives rise first to asexual spores (conidia), then to the sexual fruiting bodies (ascocarps; perithecia). Sclerotia are hard resting structures that later (after incubation on the ground) germinate to form stipate stromata. Depending on the fungus species, the host tissues on which stromata or sclerotia are produced may be young inflorescences and surrounding leaves, individual florets, nodes, or small segments of the leaves. Young stromata are hyaline (colorless), and as they mature they turn dark gray, black, or yellow-orange. Mature stromata eject meiotically derived spores (ascospores), which are ejected into the atmosphere and initiate new plant infections (horizontal transmission). In some cases no stroma or sclerotium is produced, but the fungus infects seeds produced by the infected plant, and is thereby transmitted vertically to the next host generation. Most Epichloë species, and all asexual species, can vertically transmit.
The taxonomic dichotomy is especially interesting in this group of symbionts, because vegetative propagation of fungal mycelium occurs by vertical transmission, i.e., fungal growth into newly developing host tillers (=individual grass plants). Importantly, many Epichloë species infect new grass plants solely by growing into the seeds of their grass hosts, and infecting the growing seedling.[10][11] Manifestation of the sexual state — which only occurs in Epichloë species — causes "choke disease", a condition in which grass inflorescences are engulfed by rapid fungal outgrowth forming a stroma. The fungal stroma suppresses host seed production and culminates in the ejection of meiospores (ascospores) that mediate horizontal (contagious) transmission of the fungus to new plants.[10] So, the two transmission modes exclude each other, although in many grass-Epichloë symbiota the fungus actually displays both transmission modes simultaneously, by choking some tillers and transmitting in seeds produced by unchoked tillers.
While being obligate symbionts in nature, most epichloae are readily culturable in the laboratory on culture media such as potato dextrose agar or a minimal salts broth supplemented with thiamine, sugars or sugar alcohols, and organic nitrogen or ammonium.[12]
Epichloë species are commonly spread by flies of the genus Botanophila. The flies lay their eggs in the growing fungal tissues and the larvae feed on them.[13]
The epichloae display a number of central features that suggest a very strong and ancient association with their grass hosts. The symbiosis appears to have existed already during the early grass evolution that has spawned today's pooid grasses. This is suggested by phylogenetic studies indicating a preponderance of codivergence of Epichloë species with the grass hosts they inhabit.[14] Growth of the fungal symbiont is very tightly regulated within its grass host, indicated by a largely unbranched mycelial morphology and remarkable synchrony of grass leaf and hyphal extension of the fungus;[15][16] the latter seems to occur via a mechanism that involves stretch-induced or intercalary elongation of the endophyte's hyphae, a process so far not found in any other fungal species, indicating specialized adaptation of the fungus to the dynamic growth environment inside its host.[17] A complex NADPH oxidase enzyme-based ROS-generating system in Epichloë species is indispensable for maintenance of this growth synchrony. Thus, it has been demonstrated that deletion of genes encoding these enzymes in Epichloë festucae causes severely disordered fungal growth in grass tissues and even death of the grass plant.[18][19]
Molecular phylogenetic evidence demonstrates that asexual Epichloë species are derived either from sexual Epichloë species, or more commonly, are hybrids of two or more progenitor Epichloë species.[20][21]
Many Epichloë endophytes produce a diverse range of natural product compounds with biological activities against a broad range of herbivores.[22][23] The purpose of these compounds is as a toxicity or feeding deterrence against insect and mammalian herbivores.[24] Ergoline alkaloids (which are ergot alkaloids, named after the ergot fungus, Claviceps purpurea, a close relative of the epichloae) are characterized by a ring system derived from 4-prenyl tryptophan.[25] Among the most abundant ergot alkaloids in epichloë-symbiotic grasses is ergovaline, comprising an ergoline moiety attached to a bicyclic tripeptide containing the amino acids L-proline, L-alanine, and L-valine. Key genes and enzymes for ergot alkaloid biosynthesis have been identified in epichloae and include dmaW, encoding dimethylallyl-tryptophan synthase and lpsA, a non-ribosomal peptide synthetase.[25]
Another group of epichloë alkaloids are the indole-diterpenoids, such as lolitrem B, which are produced from the activity of several enzymes, including prenyltransferases and various monooxygenases.[26] Both the ergoline and indole-diterpenoid alkaloids have biological activity against mammalian herbivores, and also activity against some insects.[22] Peramine is a pyrrolopyrazine alkaloid thought to be biosynthesized from the guanidinium-group-containing amino acid L-arginine, and pyrrolidine-5-carboxylate, a precursor of L-proline,[27][28] and is an insect-feeding deterrent.[28] One gene required for peramine synthesis – perA – was found by Tanaka et al., 2005.[28] The loline alkaloids[29] are 1-aminopyrrolizidines with an oxygen atom linking bridgehead carbons 2 and 7, and are biosynthesized from the amino acids L-proline and L-homoserine.[30] The lolines have insecticidal and insect-deterrent activities comparable to nicotine.[29] Loline accumulation is strongly induced in young growing tissues[31] or by damage to the plant-fungus symbiotum.[32] Many, but not all, epichloae produce up to three classes of these alkaloids in various combinations and amounts.[22] Recently it has been shown that Epichloë uncinata infection and loline content afford × Festulolium grasses protection from black beetle (Heteronychus arator).[33]
Many species in Epichloë produce biologically active alkaloids, such as ergot alkaloids, indole-diterpenoids (e.g., lolitrem B), loline alkaloids, and the unusual guanidinium alkaloid, peramine.[22]
It has been proposed that vertically transmitted symbionts should evolve to be mutualists since their reproductive fitness is intimately tied to that of their hosts.[34] In fact, some positive effects of epichloae on their host plants include increased growth, drought tolerance, and herbivore and pathogen resistance.[10][35] Resistance against herbivores has been attributed to alkaloids produced by the symbiotic epichloae.[22] Although grass-epichloë symbioses have been widely recognized to be mutualistic in many wild and cultivated grasses, the interactions can be highly variable and sometimes antagonistic, especially under nutrient-poor conditions in the soil.[36]
Due to the relatively large number of grass species harboring epichloae and the variety of environments in which they occur, the mechanisms underlying beneficial or antagonistic outcomes of epichloë-grass symbioses are difficult to delineate in natural and also agricultural environments.[10][37] Some studies suggest a relationship between grazing by herbivores and increased epichloë infestation of the grasses on which they feed,[38][39] whereas others indicate a complex interplay between plant species and fungal symbionts in response to herbivory or environmental conditions.[40] The strong anti-herbivore activities of several bioactive compounds produced by the epichloae [22][27] and relatively modest direct effects of the epichloae on plant growth and physiology[41][42] suggest that these compounds play a major role in the persistence of the symbiosis.
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: CS1 maint: multiple names: authors list (link) Epichloë is a genus of ascomycete fungi forming an endophytic symbiosis with grasses. Grass choke disease is a symptom in grasses induced by some Epichloë species, which form spore-bearing mats (stromata) on tillers and suppress the development of their host plant's inflorescence. For most of their life cycle however, Epichloë grow in the intercellular space of stems, leaves, inflorescences, and seeds of the grass plant without incurring symptoms of disease. In fact, they provide several benefits to their host, including the production of different herbivore-deterring alkaloids, increased stress resistance, and growth promotion.
Within the family Clavicipitaceae, Epichloë is embedded in a group of endophytic and plant pathogenic fungi, whose common ancestor probably derived from an animal pathogen. The genus includes both species with a sexually reproducing (teleomorphic) stage and asexual, anamorphic species. The latter were previously placed in the form genus Neotyphodium but included in Epichloë after molecular phylogenetics had shown asexual and sexual species to be intermingled in a single clade. Hybrid speciation has played an important role in the evolution of the genus.
Epichloë species are ecologically significant through their effects on host plants. Their presence has been shown to alter the composition of plant communities and food webs. Grass varieties, especially of tall fescue and ryegrass, with symbiotic Epichloë endophyte strains, are commercialised and used for pasture and turf.
Epichloë, aŭ Epichloe, estas genro de fungoj el la familio Klavicipitacoj (Clavicipitaceae). Ili zonas la tigon de pooideoj kun iliaj koloraj stromoj. Iliaj anamorfoj nomiĝas Neotyphodium.
Persoon nomigis Epichloë typhina kiel Sphaeria typhina en 1798 kaj Tulasne en 1865 priskribis la ĝenron Epichloë.
En 1863 Heinrich Anton de Bary malkovris la fungon ene la tigo.
Konidioj estas ovoformaj aŭ navoformaj. Fajnaj tordataj micelioj kreskas inter la ĉeloj de la tigo aŭ de la folioj. Ne estas micelioj en la radikoj. La fungo povas sin transdoni dumaniere. Senseksa, la micelio iras en grajnon kiu transdonas la fungon. Alie la fungo formas stromon cirkaŭ la tigo. Iliaj konidioj produktataj en stromoj estas transsendi de muŝoj kaj permesas seksan reproduktadon kaj estigon de peritecioj.
La fungo kiu vivas ene de la planto donas la iliaj gastigantoj utilojn. Oni parolas pri simbiozo. Li povas danke al iliaj ergotalkaloidoj protekti kontraŭ herbomanĝuloj. Li povas ankaŭ helpi kontraŭ sekeco.
White kaj al.. (2003) Clavicipitalean Fungi.
Epichloë, aŭ Epichloe, estas genro de fungoj el la familio Klavicipitacoj (Clavicipitaceae). Ili zonas la tigon de pooideoj kun iliaj koloraj stromoj. Iliaj anamorfoj nomiĝas Neotyphodium.
Epichloe (ou Epichloë) est un genre de champignons ascomycètes de la famille des Clavicipitaceae, parasite de graminées.
Le champignon forme un manchon appelé « quenouille » autour de tiges de graminées de la sous-famille des Pooideae, empêchant ainsi la formation de l'épi[3].
L'échange de gamètes se fait par l'intermédiaire de mouches du genre Botanophila. Les femelles du diptère sont attirées par les composés volatiles produits par le champignon pondent sur les jeunes quenouilles blanches et, après l'éclosion des œufs, les larves des mouches consomment les tissus et les spores du champignon jusqu'à maturité. Lors de ce processus, les femelles se nourrissent des tissus du champignon contenant des spermaties et défèquent sur toute la longueur du stroma. Les spermaties n'étant pas endommagées dans l'intestin de la mouche sont déposées sur les stromas suivants que la mouche visite. Les champignons Epichloë sont auto-incompatibles et, par conséquent, les mouches fécondent les champignons de manière croisée. Il s'agit d'un équivalent à la pollinisation entomophile unique dans le règne des Fungi.[4],[5]. Les mouches Botanophila semblent être les principaux vecteurs de spores bien que d'autres vecteurs, comme les limaces, aient été impliqués[6].
La fécondation permet la formation abondante de périthèces et le stroma prend alors une couleur orange marquée. La contamination des chaumes par les ascospores se fait au niveau des stigmates ou au niveau de blessures comme les plaies de coupe ou les morsures de l'insecte[7],[8].
Ce mutualisme semble plutôt stable. Cependant, le taux de mortalité larvaire a tendance à augmenter avec la densité d'œufs de Botanophila sur un stroma[9]. De plus, la relation entre la mouche Botanophila et l'Epichloe est limitée par le parasite sexuel bactérien du genre Wolbachia qui diminue drastiquement la présence de mâles et par conséquent la fécondation des femelles. Une hypothèse voudrait que les Epichloe puissent moduler le développement de la bactérie entomopathogène par la production d'agents antimicrobiens, ce qui induirait une réponse à la surexploitation des larves et une stabilisation dans la relation Epichloe-Botanophila[10].
La reproduction d'Epichloe peut être également purement végétative. Le mycélium se développe de façon invisible à l'œil nu à l'intérieur de la plante et migre dans la semence permettant ainsi la multiplication du champignon[11]. Le champignon peut également se maintenir dans la partie basse de la plante et réapparaitre plusieurs années sur le même pied.
Liste des espèces selon MycoBank (4 mai 2022)[2] :
Epichloe (ou Epichloë) est un genre de champignons ascomycètes de la famille des Clavicipitaceae, parasite de graminées.
Epichloë je to je zorta grzibōw. Epichloë nŏleży do familije Clavicipitaceae, rzyndu Hypocreales, klasy Sordariomycetes, grōmady Ascomycota i krōlestwa grzibōw.[1][2]
Epichloë je to je zorta grzibōw. Epichloë nŏleży do familije Clavicipitaceae, rzyndu Hypocreales, klasy Sordariomycetes, grōmady Ascomycota i krōlestwa grzibōw.