Phylum Ascomycota Kingdom Fungi Higher fungi Two phyla
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Phylum - Ascomycota Kingdom - Fungi
Higher fungi • Two phyla – Ascomycota and Basidiomycota • Thallus in both consists of sepatate hyphae that form extensive mycelia • Septa have pores that allow migration of cytoplasm, organelles and nuclei (specialized septa in Basidiomycota) • Compartments contain multiple nuclei
Higher fungi • Vegetative hyphae can fuse with one another = anastomosis (does not occur in lower fungi) • Asexual reproduction by conidia on conidiophores
Higher fungi • In sexual cycle, plasmogamy is separated from karyogamy – produces dikaryotic phase • Sexual reproduction produces spores after meiosis – ascospores or basidiospores (1 n)
Ascomycota • General characterisitics • Generally have a similar sexual life cycle • All produce an ascus (saclike structure) that contains haploid (1 n) ascospores after meiosis • Includes ~75% of the described fungi – 30, 000 spp. + 20, 000 anamorphs
Ascomycota • Sexual life cycle is basically similar – haploid-dikaryotic life cycle • Vegetative phase is haploid mycelium that may reproduce asexually by formation of conidia • Plasmogamy is separated from karyogamy in time so that a dikaryotic phase is produced – the ascogenous hyphae represent the dikaryotic hyphae
Gametangia • Male gametangia may be an antheridium or conidium-like structure – spermatium • Female gametangium = ascogonium, may have a long projection, the trichogyne
Gametangia
Plasmogamy • Male element fuses with trichogyne of the ascogonium, nuclei migrate into the ascogonium to begin the dikaryotic condition • After plasmogamy, two hyphal systems begin to grow – Sterile haploid hyphae envelope the ascogonium to form the multicellular ascoma (fruiting body) – Dikaryotic ascogenous hyphae grow from ascogonium – will give rise to the asci
Ascogenous hyphae • Male and female nuclei divide conjugately to maintain the dikaryotic condition • Many ascogenous hyphae produced inside the developing ascoma • Tips of ascogenous hyphae form croziers (hooks) before developing into an ascus
Developing ascoma • Ascoma contains two types of hyphae • Ascogenous hyphae – dikaryotic, form asci through crozier formation • Sterile hyphae – haploid, form bulk of ascoma
Crozier and ascus formation • During ascus formation, karyogamy occurs to form diploid nucleus followed by meiosis to form 4 haploid nuclei Mitosis Meiosis Karyogamy
Ascus formation • Most asci are cylindrical, but may be globose • 8 ascospores/ascus is a common number but this may vary • In most, ascogenous hyphae continue to proliferate, forming more croziers and more asci
Types of asci • Great deal of variation in asci and ascospores • Three basic types of asci • Prototunicate asci – thin, delicate wall that deliqueses to release ascospores
Types of asci • Unitunicate asci – ascus wall layers adhere closely to one another, ascospores released through a pore, a slit or an operculum (hinged cap) • Operculate asci • Inoperculate asci
Types of asci • Bitunicate asci – two wall layers that separate with the inner wall expanding, ascospores released through a pore
Fruiting bodies - ascomata • In most, the ascogenous hyphae are produced only in the ascoma (pl. ascomata • Ascomata consist of two types of hyphae – dikaryotic ascogenous hyphae that form the asci and haploid sterile hyphae that form the bulk of the ascoma • Four major types of ascomata
Cleistothecium • The cleistothecium remain closed until broken by internal forces, the asci are produced randomly within the ascoma
Perithecium • Begins as a closed structure but produces a pore at maturity through which the ascospores can escape • Asci produced in a definite layer hymenium
Apothecium • Ascoma is open when asci mature, asci are produced in an hymenium
Ascostroma • Asci are produced in a cavity (locule) within a mass of sterile tissue = stroma • No ascoma wall as stroma did not originate from ascogonium
Ascomycota classification • Currently in a state of flux • Most current treatments do not divide into classes, but rather orders • 43 (35) orders have been proposed in the Ascomycota, some of these only occur in lichens
Ascomycota classification • We will examine these fungi as: – Cleistothecial Ascomycota – Perithecial Ascomycota – Apothecial Ascomycota – Pseudothecial Ascomycota – Non ascomatal Ascomycota - yeasts • Will discuss representatives within each of these groups to get an introduction to the Ascomycota
Cleistothecial Ascomycota • Cleistothecia are the simplest type of ascoma • Surrounded by relatively simple tissue (loose hyphae), do not have an opening, are broken open • Asci are scattered • Asci are prototunicate, globose to pear shaped
Cleistothecial Ascomycota • Include species that grow as saprotrophs on keratin (protein in hair, nails) • Contains the teleomorphs of human pathogens – Dermatophytes – cause superficial skin infections such as atheletes foot – Anamorphs are Trichophyton and Microsporium • Also contains fungi that cause deep or systemic infections of humans – Ajellomyces, the teleomorph of Histoplasma capsulatum which causes histoplasmosis – Blastomyces which causes blastomycosis
Aspergillus & Penicillium • The anamorphic stages (Aspergillus and Penicillium) – better known than the teleomorphs • Asci are spherical to club shaped, ascus wall dissolves at maturity leaving ascospores free inside the cleistothecium • Most are saprotrophs • Widespread in soil, litter • Opportunistic human & animal pathogens – aspergilloses, penicilloses
Aspergillus & Penicillium • Important industrial organisms, used in making – – Chemicals – citric, gluconic & other organic acids – Antibiotics – penicillin, griseofulvin – Production of miso and soy sauce, sake – Cheese production – blue cheese and camembert • Also important in food spoilage – Citrus fruits – Grains & peanuts – produce mycotoxins
Aspergillus • Anamorphic genus – close to 100 species • 11 different teleomorphic genera produce Aspergillus conidia and conidiophores, including Eurotium, Emericella • Common fungi found in air, soil, water • Grow on a variety of substrates, in humid climates found growing on clothing, shoes, etc. • Important as contaminants of stored grain, species produce aflatoxin
Aspergillus • Produce characteristic conidiophore • Conidia produced by phialides – flask shaped conidiogenous cells • Have a characterisitic foot cell
Penicillium • Over 95 species connected to 3 teleomorphic genera – Talaromyces, Eupenicillium, Carpentales • Very common in soil, conidia found in air, water, soil • Food spoilage – on citrus fruits, jelly, cheeses • Produce penicillin and other chemicals industrially • P. roqfertii, P. camembertii used to make cheeses
Penicillium • Asexual conidiophore – not swollen at tip, no foot cell • Phialides arranged in a brushlike manner
Powdery mildews • Ascomata do not form opening so can be termed cleistothecia, but are more like perithecia without an opening – Asci occur in an irregular layer, not scattered – Asci are unitunicate, forcibly discharge ascospores through a slit • Produce colorless hyphae on surface of plant host • Produce haustoria that penetrate epidermal cells of host
Asexual reproduction • Hyphae produce chains of conidia during growing season (spring and summer) on surface of plant leaf – giving the powdery, white appearance
Sexual reproduction • Late in growing season, as plants begin to senesce, ascomata are produced – thought to overwinter as ascomata • Ascomata are closed, have characteristic appendages extending from them • Asci are globose to ovoid, generally one to a few asci/ascoma
Ascoma • Appendages
Perithecial Ascomycota • Ascoma is a perithecium • Has an opening through which ascospores leave the ascoma = ostiole • Asci produced in a layer = hymenium • Asci are unitunicate and inoperculate • Asci typically have a pore or slit at the thickened tip
Perithecial Ascomycota • A large and diverse group of fungi –(have already discussed the powdery mildews which are sometimes included here • Include species which are – Saprotrophs – wood, dung, soil, plant litter – Parasites – plant, animal (arthropod) diseases – Endophytes – Some produce mycotoxins
Perithecia • Typically flask shaped structures • Pore with opening = ostiole • Perithecial wall composed of pseudoparenchyma tissue • Centrum is the central part where asci develop
Perithecia • Perithecial wall composed of fungal tissue called pseudoparenchyma – thin cell walls, looks like plant parenchyma tissue • Centrum – the asci and sterile structures that fill the cavity within the perithecial wall • Sterile structures: – Paraphyses – basally produced in hymenium – Pseudoparaphyses – originate from top of the perithecium, grow into hymenium – Periphyses – extending into the ostiole
Ostiole Periphysis Perithecium • Classification is Stroma based in large part on development of centrum, Paraphysis Ascus development of Ascospore paraphyses or pseudoparaphyses Wall
Perithecia • Perithecia may be produced individually or they may be produced within a mass of tissue = stroma (always produce a separate perithecial wall)
Stroma (stromata) • Compact tissue that forms a flat plate or a mass • Hyphae may be inflated, intertwined, have lost identity to form a tissue that looks like parenchyma tissue of plants – called pseudoparenchyma • May be hard and woody or soft and fleshy
Perithecial Ascomycota • Saprotrophic fungi on dung, wood, in soil & decaying leaves • Includes Neurospora – important in study of genetics • Asci are club shaped to cylindrical, most produce 8 ascospores • Asci may breakdown and release ascospores or persist & forcibly discharge ascospores
Chaetomium • Common saprotrophs in soil and dung, highly cellulolytic • Perithecia have distinctive filaments (straight or spiral )extending from upper part of perithecium • Asci are club shaped and wall deliqueses leaving ascospores embedded in jelly like substance that oozes out of the ostiole
Chaetomium • Ascospores are lemon shaped
Neurospora crassa • Red (pink) bread mold – grows on dough in bakeries, forms lots of conidia, bad contaminant • Widely used in genetic studies, one gene – one enzyme concept developed in Neurospora • Most species are heterothallic – two mating types – A & a
Sordaria perithecia & asci
Ascospore discharge • In many Ascomycota, asci develop high turgor pressure and actively discharge ascospores individually or as a group from ascus • In some, particularly coprophilous forms, the asci or ascomata may be phototrophic so that ascospores are discharged toward the light
Ascospore discharge • In Sordaria, Neurospora and other members of this group, asci stretch through ostiole and actively discharge ascospores
Xylaria • Produce dark colored, brittle solitary perithecia or perithecia may be produced in a stroma • Stromata are hard and woody, generally dark colored • In development of centrum, paraphyses grow from base and sides to expand the perithecium that allows the asci space – paraphyses may persist or disappear
Xylaria • Forms a dark colored, woody stroma, ca 10 cm long and 1 -2 cm in diam • Extends up from ground, grows on wood • Commonly called “dead man’ s fingers”
Nectria • Produce brightly colored stromata that are generally soft and fleshy with embedded perithecia • Includes both plant and fungal parasites
Claviceps purpurea • Ascospores produced in spring – infect the ovaries of rye flowers • Hyphae grow and replace ovary tissue, forming a hyphal mat that produces small conidiophores and conidia, secretes a nectar like substance that attracts insects for dispersal to other plants • Mycelial mat differentiates – becomes hardened and forms pseudoparenchyma – eventually becoming a sclerotium
Claviceps purpurea • Sclerotium – firm mass of fungal tissue, resistant to environmental extremes, can remain dormant • Falls to ground & overwinters as a sclerotium
Claviceps purpurea • In spring, sclerotia germinate to produce stalked stromata within which perithecia are produced
Claviceps life cycle
Ergotism • If sclerotia are harvested with grain and ground into flour, they contain a number of alkaloids that are poisonous to humans and animals – cause ergotism • Latest epidemic in 1951 in France resulted in several deaths and many sick and crippled people – also called St. Anthony’s fire • Symptoms – vomiting, intense cold or hot sensations, lesions on hands and feet, diarrhea, convulsions, gangrenous condition in limbs that may lead to loss, causes constriction of arteries and contraction of smooth muscle
Ergotism • In 1951, some people suffered from hallucinations • Concluded that these were similar to LSD (lysergic acid diethylamide) • LSD not produced by Claviceps, but thought that other fungi converted some of the alkaloids produced to LSD
Ergotism • Ergotism thought to have caused symptoms that lead to the Salem witch trials • Ergot alkaloids in the proper dose have been used in medicine – Stimulate labor – sclerotia carried by midwives – Treatment of migraines • Alkaloids only produced by sclerotium, not by mycelium – until recently had to infect fields of rye to obtain sclerotia, recent methods have produced alkaloids in culture
Cordyceps • Parasite of insects and fungi forms stromata from host
Apothecial Ascomycota • Unitunicate asci • Operculate & inoperculate asci • Asci present in a hymenium • Ascoma is open & hymenium exposed when asci mature
Apothecia • Range in size from microscopic to morels • Many called cup fungi since apothecium forms a cup, others may be flat, disk shaped or stalked • Truffles produce a modified apothecium
Apothecia • • Most are produced above ground = epigean Some are produced below ground = hypogean Asci are typically club shaped or cylindrical Most actively discharge ascospores distances from 2 -30 cm • Simultaneous discharge of many asci causes wind currents that may carry ascospores farther – puffing • Puffing caused by changes in humidity, wind, etc
Puffing
Apothecial development in Ascobolus
Apothecia in Pezizales • Cup-shaped apothecia – Stalked – Sessile
Morels and relatives • Morchella • Modified apothecia
Morels • False morels - Verpa
False morels • Gyromitra • Helvella
Truffles • Truffles produce hypogeous ascomata • Ascomata are highly modified • Hymenium has great deal of infolding • Ascospores not forcibly ejected
Truffles • Ascomata broken open by animals or by weathering • Some species emit strong odor so that small animals, insects can detect them underground, dig up and eat them, dispersing spores • Geopora, Tuber
Truffles • Ascomata of Tuber thought to be the best fungi to consume • Are mycorrhizal with certain trees (oaks, hazelnuts) • Use trained pigs and dogs to find them
Pseudothecial Ascomycota • Ascoma produced by these fungi is an ascostroma – asci are produced in cavities (locules) in a stroma, no separate wall around ascoma, only stroma • In some, superficially look like perithecia
Asci • Most produce bitunicate asci • Two layers that separate when mature
Ascomycota - yeasts • Produce naked asci, never produce ascomata or ascogenous hyphae • Include single cell and filamentous yeasts • Cell wall polysaccharides include mannans, glucans plus small amount of chitin • DNA sequences indicate that these yeasts are a monophyletic group sister to the filamentous Ascomycota
Yeasts • Many species associated with flowers, fruits where high concentrations of sugar are present • Many are facultative anaerobes – aerobic respiration or ethanol fermentation • Widely used in brewing (beer, wine) and baking industries • Some used as human & animal food, source of vitamins • Also include some human pathogens – Candida albicans – normal flora
Yeasts • Thallus is typically unicellular, in some species there may be a limited mycelium (filamentous yeasts) • Asexual reproduction – cell division in unicellular forms • Commonly occurs as budding – unequal cell division where a daughter cell grows larger until it separates from mother cell
Budding
Sexual reproduction • Haploid-diploid life cycle as in Saccharomyces cerevisiae (baker’s and brewer’s yeast)
Taphrinales • Pathogens of plants • Cause peach leaf curl, witches broom, shriveled pocket of plum and others
Taphrinales • Produce dikaryotic hyphae in the host tissue that give rise to naked asci (no ascoma) • Asci split across the top to release ascospores (not typical of other Ascomycota)
Ascomycota - review • Large phylum – ca 30, 000 spp. • Most form septate hyphae, some have unicellular thallus • Sexual life cycle – produce ascus with haploid ascospores after meiosis • Vegetative thallus is haploid • Dikaryotic stage is extended – ascogenous hyphae
Ascomycota - review • Most produce multicellular fruting body – the ascoma in which the asci and ascospores are formed • An ascoma contains two types of hyphae – Haploid hyphae that form the wall and sterile structures (paraphyses) – Dikaryotic ascogenous hyphae in which karyogamy and meiosis occur • Characterisitics of asci and ascoma important in classification
Ascomycota - review • Asexual reproduction – production of conidia on conidiophores • Represents the anamorphic stage • Many of the Deuteromycota thought to be anamorphs of Ascomycota
Ascomycota - review • Phylogeny • Previous hypotheses that the Ascomycota evolved from red algae (similarities in morphology of sexual structures) and Mucorales • Evidence from DNA sequences suggests that Ascomycota and Basidiomycota are sister groups but to date no indication of ancestors
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