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 (1n)

Ascomycota General characterisitics Generally have a similar sexual life cycle All produce an ascus (sac-like structure) that contains haploid (1n) 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

Perithecium Ostiole Periphysis Wall Classification is based in large part on development of centrum, development of paraphyses or pseudoparaphyses Stroma Paraphysis Ascus Ascospore

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