Ascomycota
From Palaeos
| FUNGI | ||||
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Fungi |--Chytridiomycota `--+--o--Zygomycetes | `--Trichomycetes `--+--Basidiomycota | |--Ustilaginomycetes | `--Hymenomycetes `--Ascomycota |--Saccharomycotina `--Pezizomycotina (See also Alternative phylogeny) |
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Contents |
[edit] Introduction to the Ascomycota
The Ascomycota are the largest and most diverse group of Fungi. They include the yeasts, most of the fungal elements of lichen, and such famous Fungi as Saccharomyces, Aspergillus, Candida and Neurospora, as well as morels, truffles and similar delicacies. The current understanding is that supposed pre-Devonian (even Proterozoic!) lichens are probably artifacts, making the earliest known ascomycote of Carboniferous age.
Ascomycetes are united by the presence of asci. Like Basidiomycota, ascomycetes remain indefinitely in the dikaryon state, with the fungal filaments (hyphae) partitioned into cells each containing two haploid nuclei -- one from each parent. Also as in basidiomycetes, nuclear fusion (karyogamy) occurs only in connection with the formation of sexual spores. At that time the newly diploid nucleus undergoes one (sometimes more) round of mitosis, followed by meiosis, to yield eight (or a multiple of eight) haploid nuclei. The nuclei are then partitioned by internal membranes into individual ascospores. The Ascomycota also share with Basidiomycota the use of conidia for the development of asexual spores.
| ASCOMYCOTA | |
| Taxonomy | Phylogeny |
Kingdom: Fungi
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o Fungi `--o Ascomycota |--Taphrinomycotina `--+--Pezizomycotina `--Saccharomycotina
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[edit] Characteristics
Other than the ascus, not a great deal unites the Ascomycota. Almost all ascomycetes are terrestrial or parasitic. However, a few have adapted to marine or freshwater environments. The cell walls of the hyphae are variably composed of chitin and β-glucans, just as in Basidiomycota. However, these fibers are set in a matrix of glycoproteins containing the sugars galactose and mannose, rather than xylose and mannose as in Basidiomycota [1].
The mycelium of ascomycetes is usually made up of septate 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 of Woronin bodies on each side of the septa separating the hyphal segments which control these 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. More derived ascomycetes may have, in addition, septal pore organelles which isolate portions of the mycelium which are undergoing sexual reproduction.
Mycologists long ago learned the same trick which has more recently been discovered by television programming executives. The secret is this: regardless of phylogenetic position, reproductive behavior and physiology lend themselves to the creation of strong and attractive images which enable one to go on for hours without really having to communicate a great deal of substance. In addition, ascomycetes, like the characters in situation comedies, seem to lead sex lives of utterly unreasonable complexity. Sadly, the resemblance ends there, or mycology would be considerably more popular than it is. Quite aside from issues of physical aesthetics, Fungi simply lack the native ability to make us identify with their unrequited yearnings for hyphae of the opposite mating type. Even such dramatic events as ballistospory (quite common among ascomycetes) cannot disguise the fact that this is, fundamentally, a rather tedious business once we get past the usual colorful diagram.
At any rate, we have now provided a suitably edifying chart with which to illumine the dark night of ignorance, etc. So, our work here is done; and we may return to matters of more intrinsic interest, secure in the knowledge that our duty to a century of mycological tradition has been fully performed.
It is worth noting that ascomycetes tend to have special relationships with insects. Some are "farmed" by beetles and social insects, while others are parasitic on insects. Yet others produce powerful toxins which are relatively specific to insects. Since both insects and ascomycetes are largely terrestrial and both experienced their first major radiation in the Mississippian, it may be that they shared some significant resource or niche. However, the great expansion of insect life probably took place in the Serpukhovian, quite late in the Mississippian, and was most closely related to the evolution of flight.
Another notable ecological link is the relationship between ascomycetes and plant life. Both basidiomycetes and ascomycetes developed the ability to digest plant tissues early on. This was a critical development, since the explosive spread of land plants in the Late Devonian and Mississippian was burying atmospheric carbon dioxide at a ferocious rate and increasing oxygen to the point that it became -- explosive. Basidiomycetes and ascomycetes evolved a sort of division of labor in handling this important bit of recycling. Basidiomycetes do most of the heavy lifting by digesting cellulose (brown rot) and lignin (white rot). However, ascomycetes do their bit by digesting the other glucans which hold the other plant materials together (soft rot). The effects of soft rot are shown -- from a most unusual source -- in the image. Filley et al. (2001). Thus the ascomycetes are important in making plant tissues accessible to attack by basidiomycetes. It seems we have the fungi to thank for saving us from a world caught in an unstable alternation between frozen wastes and exploding forests.
[edit] Phylogeny
It is now generally accepted that Ascomycota and Basidiomycota are sister clades, since they share a number of synapomorphies, including septate mycelia, a dikaryotic stage in the life cycle, plectenchymatous structures associated with spore production, and conidia. The only weak spot in this reasoning is that the yeasts, which are rather basal ascomycetes, are secondarily (probably) unicellular and lack some of these multicellular synapomorphies. However, both molecular and morphological comparisons place the yeasts comfortably within the Ascomycota, and most workers are willing to accept that they derived from a yet more basal multicellular ascomycete ancestor with the appropriate characteristics. A certain amount of this sort of thing is likely, given that Ascomycota has a ghost lineage of about 60 My, i.e., the time between the first known appearance of Basidiomycota and the first clear remains of Ascomycota.
The ascomycetes were traditionally divided into the Hemiascomycetes and the Euascomycetes, sometimes with the addition of a probably paraphyletic basal group called Archaeascomycetes. Bold (1973). More recently, mycology was seduced by the spell of the Svengalis of Sequencing, with the usual disastrous abandonment of useful nomenclature. We often resist using molecular nomenclature because it is only useful when discussing sequence data and seems to represent a willful rejection of everything else. Like the "Newspeak" of George Orwell's 1984, molecular nomenclature tends to make certain thoughts impossible by denying them a convenient linguistic point of reference. However, at least for the Fungi, we acknowledge the superior pressure of competing considerations, discussed elsewhere. For those reasons we have adopted the new words. For those who wish to mentally translate:
Taphrinomycotina = Archaeascomycetes Saccharomycotina = Hemiascomycetes Pezizomycotina = Euascomycetes
In even older literature, the ascomycetes, as we presently understand them, were divided between two groups, the Ascomycota and the Deuteromycota. The latter were often referred to as fungi imperfecti, i.e., species of fungi for which no sexual stage was known. It is now known that these “imperfect fungi”, formerly Class Hyphomycetes in the Deuteromycota, are anamorphs (asexual forms) of the ascomycetes [2].
<==Ascomycota [Ascomycotina, Hemiascomycotina] | i. s.: Coryneliaceae [Coryneliales] | |--Bicornispora | |--Caliciopsis | |--Corynelia | |--Coryneliopsis | |--Coryneliospora | |--Fitzpatrickella | |--Lagenulopsis | `--Tripospora | Lahmia [Lahmiaceae, Lahmiales] | Medeolaria [Medeolariaceae, Medeolariales] | Triblidiaceae [Triblidiales] | |--Huangshania | |--Pseudographis | `--Triblidium | Trichotheliales | Amorphotheca [Amorphothecaceae] | Aphanopsis [Aphanopsidaceae] | Diporotheca Gordon & Shaw 1960 [Diporothecaceae] | Eoterfeziaceae | |--Acanthogymnomyces | `--Eoterfezia | Epigloea [Epigloeaceae] | Koralionastes [Koralionastetaceae] | Lautospora [Lautosporaceae] | Mastodiaceae | |--Mastodia | `--Turgidosculum | Microcalicium [Microcaliciaceae] | Phyllobatheliaceae | |--Phyllocratera | |--Opercularia firma | `--Phyllobathelium [incl. Septoriomyces] | `--P. leguminosae (Cavalc. & Silva) Lücking & Sérus 1998 (see below for synonymy) | Pleurotremataceae | |--Daruvedia | `--Pleurotrema | Protothelenellaceae | |--Mycowinteria | `--Prothelenella | Saccardiaceae | Seuratiaceae | |--Seuratia | `--Seuratiopsis | Strigulaceae | |--Oletheriostrigula | |--Phylloblastia | `--Strigula (see below for synonymy) | |--S. antillarum [incl. *Pycnociliospora belluciae] | |--S. multipunctata [incl. *Manaustrum palmae] | |--S. nemathora [incl. *Amoebomyces pseudolmediae] | |--S. platypoda [incl. *Didymaster myrtaciicola] | `--S. prasina [incl. *Kilikiostroma peresii] | Testudinaceae | |--Eremodothis | |--Lepidosphaeria | |--Neotestudina | |--Testudina | `--Ulospora | Thelocarpaceae [Thelocarpeae] | |--Melanophloea | |--Sarcosagium | `--Thelocarpon Nylander 1853 (see below for synonymy) | |--*T. albidum Nylander 1853 | |--T. citrum (Wallr.) Rossman in Rossman, Samuels et al. 1999 (see below for synonymy) | |--T. lichenicola (Fuckel) Poelt & Hafellner 1975 (see below for synonymy) | `--‘*Cyanocephalium’ murorum Zukal 1893 | Thrombium [Thrombiaceae] | Xanthopyreniaceae | |--Collemopsidium | |--Didymellopsis | |--Pyrenocollema | `--Zwackhiomyces | Calycidium [Calycidiaceae] | Allophoron | Abrothallus | Antimanoa | Argentinomyces | Arthopyreniomyces | Ascocorticiellum | Ascomauritania | Ascosorus | Ascosubramania | Ascoxyta | Astomella | Atractobolus | Baculospora | Batistospora | Berggrenia | Biflua | Bresadolina | Carnia | Clathroporinopsis | Clypeolum | Coryneliella | Coscinocladium | Crinigera | Cyanopyrenia | Cystodium | Diaboliumbilicus | Diehliomyces | Dipyrgis | Discocera | Dryinosphaera | Eiona | Elaeomyces | Endocolium | Enduria | Erispora Patouillard 1922 (n. d.) | `--*E. parasitica Patouillard 1922 (n. d.) | Farriolla | Feracia Rolland 1905 (n. d.) | `--*F. balearica Rolland 1905 (n. d.) | Flakea | Frigidospora | Gaeumanniella | Gonidiomyces | Gyrophthorus | Haematomyxa | Haplopyrenulomyces | Hapsidascus | Harmandiana | Heterocyphelium | Heuflera | Hyalodermella | Hyalopyrenula | Hypnotheca | Leucoconiella | Leucoconis | Lichenopeziza | Lithopythium | Lohwagiella | Ludwigomyces | Lyromma [incl. Anconomyces, Lyrommotheca (nom. illeg.)] | |--*L. nectandrae | |--L. dolicobelum | `--L. palmae | Marisolaris | Micromastia | Molgosphaera | Mycotodea | Myriococcum | Nemacola | Normandina | Ochrosphaera | Phacidiostromella | Phaeodothiopsis | Phellostroma | Phelonitis | Phialisphaera | Phragmitensis | Phthora | Pocsia | Porinula | Porosphaera | Potamomyces | Protocalicium | Pseudohepatica | Pseudoperitheca | Psilosphaeria | Pteromycula | Pycnodermellina | Roeslerina | Rostafinskia | Sachsia | Schistophoron | Stellifraga | Stigmatisphaera | Stigmea | Swampomyces | Syphosphaera | Telioclipeum | Thallisphaera | Trichoplacia | Trichosphaera | Tylophorella | Tylophoron | Ulvella | Wadeana | Wolkia | Xenomyxa | Xylobotryum | Xylogone | *Aciesia xylopiae (n. d.) | Pestalotia palmarum | Arthrobotryomyces amazonensis (n. d.) | Asbolisiomyces ingae (n. d.) | Astrabomyces amazonensis (n. d.) | Podoxyphiomyces manaosensis (n. d.) | *Pyriomyces protii | Fellhanera | *Pyripnomyces maranhensis | Phyllophiale [incl. Stephosia] | |--P. alba Santesson 1952 | `--P. fusca | Puiggarina costaricensis | Zeus olympius | anam. Sphaceloma ampelinum (see below for synonymy) | Porphyrosoma Patouillard 1928 (n. d.) | `--*P. episphaeria Patouillard 1928 (n. d.) [=Hypocreopsis episphaeria] | Lecythium Zukal 1893 [=Lecithium (l. c.)] | `--*L. aerugineum Zukal 1893 | Eleutheromyces subulatus (see below for synonymy) |--Taphrinomycotina `--+--Pezizomycotina `--Saccharomycotina
Eleutheromyces subulatus [=Sphaeronaema subulata, Sphaeronaemella subulata; incl. Sphaeronaema oxysporum, Sphaeronaemella oxyspora]
Phyllobathelium leguminosae (Cavalc. & Silva) Lücking & Sérus 1998 [=*Septoriomyces leguminosae]
anam. Sphaceloma ampelinum [incl. Gloeosporium ampelophagum, Fusarium cesatii, Chrysogluten cesatii]
Strigula [incl. Amoebomyces, Didymaster, Kilikiostroma, Manaustrum, Pycnociliospora]
Thelocarpon Nylander 1853 [incl. Ahlesia Fuckel 1870, Cyanocephalium Zukal 1893, Metanectria Saccardo 1878]
Thelocarpon citrum (Wallr.) Rossman in Rossman, Samuels et al. 1999 [=Sphaeria citrum Wallr. 1833, *Metanectria citrum (Wallr.) Saccardo 1878, Nectria citrum (Wallr.) Montagne 1858; incl. Thelocarpon vicinellum Nylander 1885]
Thelocarpon lichenicola (Fuckel) Poelt & Hafellner 1975 [=Peziza lichenicola Fuckel 1864, *Ahlesia lichenicola (Fuckel) Fuckel 1870]
* Type species of generic name indicated
[edit] Footnotes
[1] Two relatively recent sources have given opposite indications about the relative proportions of chitin and glycoprotein -- one stating that the wall is "mostly chitin" and the other stating that very little chitin is present. As in many areas of ascomycete biology, the degree of variation within this diverse group of fungi probably makes any generalization impossible.
[2] Note, once again, traditional mycology's fixation on sexual reproduction. Not only are fungi with no known teleomorphs excluded from the Ascomycota, but they are referred to as "imperfect." This would simply be a source of amusement, but it led to a corresponding lack of interest in matters of great importance in the vegetative state, such as the mechanisms of the ecologically critical "rots," intercellular transport and signaling, vegetative growth habits and structural biology, and so on.
[edit] References
Bold, H. C. 1973. Morphology of Plants, 3rd ed. Harper & Row.
Eriksson, O. E. (ed.) 1999. Notes on ascomycete systematics. Nos 2440-2755. Myconet 2: 1-41.
Eriksson, O. E., H. O. Barah, R. S. Currah, K. Hansen, C. P. Kurtzman, G. Rambold & T. Laessøe (eds.) 2003. Outline of Ascomycota – 2003. Myconet 9: 1-89.
Filley, T. R., R. A. Blanchette, E. Simpson & M. L. Fogel. 2001. Nitrogen cycling by wood decomposing soft-rot fungi in the “King Midas tomb,” Gordion, Turkey. Proceedings of the National Academy of Sciences of the USA 98: 13346–13350.
Hosagoudar, V. B. 2003. Armatellaceae, a new family segregated from the Meliolaceae. Sydowia 55 (2): 162-167.
Lücking, R., & A. Vězda. 1998. Taxonomic status in foliicolous species of the genus Porina (lichenized Ascomycotina: Trichotheliaceae) - II. The Porina epiphylla group. Willdenowia 28: 181-226.
Lumbsch, H. T., I. Schmitt, H. Döring & M. Wedin. 2001. Molecular systematics supports the recognition of an additional order of Ascomycota: The Agyriales. Mycological Research 105 (1): 16-23.
Miadlikowska, J., & F. Lutzoni. 2004. Phylogenetic classification of peltigeralean fungi (Peltigerales, Ascomycota) based on ribosomal RNA small and large subunits. American Journal of Botany 91 (3): 449-464.
Prescott, L. M., J. P. Harley & D. A. Klein. 1996. Microbiology (3rd ed.) Wm. C. Brown Publishers: Dubuque (Iowa).
Rossman, A. Y., G. J. Samuels, C. T. Rogerson & R. Lowen. 1999. Genera of Bionectriaceae, Hypocreaceae and Nectriaceae (Hypocreales, Ascomycetes). Studies in Mycology 42: 1-248.
Schweigkofler, W., K. Lopandic, O. Molnár & H. Prillinger. 2002. Analysis of phylogenetic relationships among Ascomycota with yeast phases using ribosomal DNA sequences and cell wall sugars. Organisms Diversity & Evolution 2: 1-17.
Credits
intro ATW041118, characteristics ATW041231, phylogeny intro ATW041231, dendrogram CKT080112
