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Phylum - Ascomycota

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Phylum - Ascomycota Powered By Docstoc
					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
             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
    Wall
                    • Classification is
    Stroma
                      based in large part
                      on development of
         Paraphysis   centrum,
           Ascus
           Ascospore
                      development of
                      paraphyses or
                      pseudoparaphyses
                    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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