Phylum: Glomeromycota Glomeromycota - Welcome to University of

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Phylum: GlomeromycotaGlomeromycota

Lecture 03

GlomeromycotaFormerly classified with Zygomycota.Recently erected into its own phylum.Say more about this group when we cover symbiosis in last lecture.

Phylum: AscomycotaAscomycota

Very difficult phylum to define.AsciAsci (sing.=ascusascus) and ascosporesascospores produced during sexual reproduction.

Phylum: AscomycotaAscomycotaAscusAscus AscosporesAscospores

Mycelium septateseptate.Thallus may also be yeastyeast: Unicellular fungi that reproduce asexually by buddingbudding or fissionfission.


Septate hyphae

YeastYeast

Budding

FissionFission: Mitosis and cell division.Some species are dimorphicdimorphic: Having yeast and mycelium produced during life cycle.Yeast and yeast-like fungi are believed to be ancestral morphology.


FissionFission

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Many different classification of Ascomycota. Will divide phylum into three groups:


Class - ArchiascomycetesArchiascomycetes: Yeast and yeast-like fungi. PolyphyleticClass - SaccharomycetesSaccharomycetes: Budding yeast. Believed to be monophyletic and not closely related to Archiascomycets.Filamentous AscomycetesFilamentous Ascomycetes: Mycelium and ascocarpascocarp produced during life cycle.

Separation of Archiascomycetes from Saccharomycetales based mostly on rDNA analysis.


Archiascomycetes is believed to be the earliest evolved group, with the filamentous Ascomycetes and Saccharomycetes being derived sister groups.

Phylogenetic Tree of Ascomycota Three ascus types:


ProtunicateProtunicate

Three ascus types (Continued):Phylum: AscomycotaAscomycota

UnitunicateUnitunicate

EndoascusEndoascus

ExoascusExoascus

BitunicateBitunicateArchiascomycetes include yeast that reproduce asexually by budding and fission, as well as dimorphic species.

Schizosaccharomyces octosporus is example of fission yeast.Taphrina deforman is example of dimorphic species.


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Schizosaccharomyces octosporus

Life cycle of a fission yeast.fission yeast.Zygotic life cycleZygotic life cycleAsci and ascospores are borne naked. Species homothallic.


Cells reproducing, asexually, by fission..


Naked ascus with eight ascospores.

Ascus was originally cell wall of zygote.

AscusAscus

AscosporesAscospores

Taphrina deformanTaphrina deforman

Summary of T.deforman life cycle.

HomothalicHomothalic and asci and ascospores naked.

DimorphicDimorphic


Cause of Peach Leaf Curl.

Asci and ascospores borne on leaf surface, at site of deformities.


Cause of Peach Leaf Curl.

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Asci and ascospores ofTaphrina deforman.

Taphrina deformanTaphrina deformanHigher Magnification.

AscusAscospore

Stalk Cell


Saprobic in yeast stage.

Mycelial stage is obligate parasite.


Parasitic, dikaryotic mycelium forms when yeast cell comes in contact with host.

Saprobic Saprobic yeast phaseyeast phase

Parasitic Parasitic mycelium mycelium phasephase

Taphrina deformanTaphrina deformanLongitudinal section of Taphrinainfection on young peach leaves.

DikaryoticDikaryoticmyceliummyceliumgrowing between host cells of leaf

Ascogenous Ascogenous cellcell CuticleCuticle

EpidermisEpidermis

Palisade Palisade parenchymaparenchyma

Taphrina deformanTaphrina deformanDevelopment of Taphrina ascus:

KaryogamyKaryogamy Mitosis of Mitosis of zygote zygote nucleusnucleus

Unequal Unequal cell divisioncell division

Ascus cellAscus cell

Stalk Stalk cellcell

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Taphrina deformanTaphrina deformanDevelopment of Taphrina ascus (Continued):

Meiosis has occurred

MitosisMitosis and ascosporeascosporeformation

AscosporeAscospore

AscusAscus

Saccharomycetes represents a monophyletic group of fungi:

Dipodascopsis uninucleatus is a yeast-like species with short hyphal growth.Saccharomyces cerevisiae is the Brewer’s Yeast of commerce.


Once thought to be link in origin of Ascomycota from Zygomycota.Species has short hyphal growth and is homothallic.Not a yeast!

Dipodascopsis uninucleatusSummary of life cycle:

Dipodascopsis uninucleatus

Ascospores germinate to produce limited, hyphal growth.Adjacent cells function as gametangia.


Plasmogamyoccurs when cell wall between gametangia dissolves.Followed bykaryogamy and meiosis.


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Ascus elongates, followed by manymitotic divisions.Results in ascus with hundreds of ascospores instead of the typical eight.


Many Many mitotic mitotic divisionsdivisions

Species heterothallicheterothallicwith mating strains designated as a and α.Plasmogamy andkarogamy of a and αmating strains forms zygote.Asci and ascospores are borne naked.

Saccharomyces cerevisiae

Yeast cell budding:


Ascus with four ascospores:


Ascus with ascospores

Introduction:Mycelium always septate, but septa incomplete, with pore in center.Pore in septa often blocked in older hyphae with woroninworonin bodiesbodies.

Filamentous AscomycetesIntroduction (continued):

Historically, classification of this group has been based on the type of ascocarp produced.Molecular analyses has demonstrated this to be an artificial form of classification, but is still the most convenient means of classifying filamentous ascomycetes.

Filamentous Ascomycetes

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Introduction (continued):Asci and ascospores borne in an ascocarp.Four types of ascocarps associated with four informal categories of ascomycetes:

Cleistothecium Cleistothecium –– PlectomycetesPlectomycetesPerithecium Perithecium –– PyrenomycetesPyrenomycetesApothecium Apothecium –– DiscomycetesDiscomycetesAscostroma Ascostroma -- LoculoascomycetesLoculoascomycetes

Filamentous AscomycetesCleistotheciumCleistothecium:

Ascocarp is entirely closed.Asci do not form a hymeniumhymenium.Usually member of PlectomycetesPlectomycetes.


Perithecia:Commonly flask-shaped.Hymenium formed.

Filamentous AscomycetesOstiole

Sterile filaments present: Paraphyses, periphyses andpseudoparaphyses present or absent.PyrenomycetesPyrenomycetes.

ApotheciumApothecium:An ascocarp that has its hymenium entirely open at maturity.Paraphyses typically present.DiscomycetesDiscomycetes.


AscostromaAscostroma:Filamentous Ascomycetes

Cavity in a stroma where asci and ascospores are borne.Loculoascomycetes.

ascocarp wall absentascocarp wall absentWill use the development of Peziza as representative of ascocarp (apothecium) development.Start at germination of ascospores to produce monokaryonmonokaryon.Monokaryons self sterile and cross fertile, i.e. heterothallic.

Ascocarp Development

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Monokaryon StrainsAscocarp Development

Each monokaryon have both ascogoniaascogonia(female gametangia) and antheridiaantheridia(male gametangia).


Ascocarp formed by tightly interwoven mycelium.

Pezizaapotheciumapothecium

Antheridial nuclei transported to the ascogoniumthrough the trichogynetrichogyne..The trichogyne is a tubular growth originating from the ascogonium.


A1 and A2 nuclei pair off in ascogonium.A1 and A2 nuclei undergo synchronous mitotic divisions.AscogenousAscogenoushyphaehyphae((dikaryondikaryon) ) form from ascogonium.

Ascocarp DevelopmentCrozierCrozier FormationFormation:


Ascogenous Ascogenous hyphahypha

CrozierCrozier

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Ascus FormationAscus Formation:Ascocarp Development

CrozierCrozier

KaryogamyKaryogamy

MeiosisMeiosis

MitosisMitosisCrozierCrozierProliferationProliferation:

Apical and stalk cells fuse.New crozierproliferates.Crozierproliferation occurs repeatedly.


Development of ascus and ascospores from new crozier:

Ascocarp DevelopmentAscogoniumforms asci, ascospores and paraphyses:paraphyses:hymeniumhymenium.


At same timeascus is developing, ascocarp is forming.Monokaryoticmyceliumdevelopes from stalk cell produce ascocarp.

Ascocarp Development L-Sect.- Mature Apothecium

Phylum: Glomeromycota Glomeromycota - Welcome to University of

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