Phylum: Glomeromycota Glomeromycota Formerly classified with Zygomycota. Recently erected into its own phylum. Say more about this group when we cover symbiosis in last lecture.
Lecture 03
Phylum: Ascomycota Ascomycota Phylum: Ascomycota Ascus Ascospores Very difficult phylum to define. Asci (sing.=ascus) and ascospores produced during sexual reproduction.
Phylum: Ascomycota Phylum: Ascomycota Fission: Mitosis and Mycelium cell division. septate. Some species are Thallus may also Budding dimorphic: Having be yeast: yeast and mycelium Unicellular fungi produced during life that reproduce cycle. asexually by Yeast and yeast-like Fission budding or fungi are believed Septate Yeast fission. hyphae to be ancestral morphology.
1 Phylum: Ascomycota Phylum: Ascomycota Many different classification of Separation of Archiascomycetes from Ascomycota. Will divide phylum into Saccharomycetales based mostly on three groups: rDNA analysis. Class - Archiascomycetes: Yeast and Archiascomycetes is believed to yeast-like fungi. Polyphyletic be the earliest evolved group, with Class - Saccharomycetes: Budding the filamentous Ascomycetes and yeast. Believed to be monophyletic and Saccharomycetes being derived not closely related to Archiascomycets. sister groups. Filamentous Ascomycetes: Mycelium and ascocarp produced during life cycle.
Phylogenetic Tree of Phylum: Ascomycota Ascomycota Three ascus types: Protunicate
Phylum: Ascomycota Phylum: Ascomycota Three ascus types (Continued): Archiascomycetes include yeast that Bitunicate reproduce asexually by budding and Endoascus fission, as well as dimorphic species. Schizosaccharomyces octosporus is Unitunicate example of fission yeast. Taphrina deforman is example of dimorphic species.
Exoascus
2 Schizosaccharomyces Schizosaccharomyces octosporus octosporus Life cycle of a fission yeast. Cells reproducing, Zygotic life cycle asexually, by Asci and fission. ascospores are borne naked. Species homothallic.
Schizosaccharomyces Taphrina deforman octosporus Summary of T. Naked ascus with deforman life eight ascospores. cycle. Ascus was Ascus Homothalic and originally cell wall asci and of zygote. ascospores naked. Ascospores Dimorphic
Taphrina deforman Taphrina deforman
Cause of Peach Cause of Peach Leaf Curl. Leaf Curl. Asci and ascospores borne on leaf surface, at site of deformities.
3 Taphrina deforman Taphrina deforman
Higher Asci and Magnification. ascospores of Taphrina Ascospore deforman. Ascus
ÍStalk Cell
Taphrina deforman Taphrina deforman
Saprobic in Parasitic, dikaryotic mycelium forms yeast stage. when yeast cell comes in contact with host. Mycelial stage is obligate Parasitic parasite. mycelium phase Saprobic yeast phase
Taphrina deforman Taphrina deforman Longitudinal section of Taphrina Development of Taphrina ascus: infection on young peach leaves. Ascogenous cell Cuticle Ascus cell Dikaryotic mycelium Stalk growing cell between Karyogamy Mitosis of Epidermis host cells Unequal of leaf zygote cell division Palisade nucleus parenchyma
4 Taphrina deforman Phylum: Ascomycota Development of Taphrina ascus (Continued): Saccharomycetes represents a monophyletic group of fungi: Ascospore Dipodascopsis uninucleatus is a yeast-like species with short hyphal Ascus growth. Saccharomyces cerevisiae is the Brewer’s Yeast of commerce.
Meiosis has Mitosis and occurred ascospore formation
Dipodascopsis uninucleatus Dipodascopsis uninucleatus Once thought to be link in origin of Summary of life cycle: Ascomycota from Zygomycota. Species has short hyphal growth and is homothallic. Not a yeast!
Dipodascopsis uninucleatus Dipodascopsis uninucleatus
Plasmogamy occurs when cell wall between gametangia dissolves. Followed by Ascospores germinate to produce karyogamy and limited, hyphal growth. meiosis. Adjacent cells function as gametangia.
5 Dipodascopsis uninucleatus Saccharomyces cerevisiae
Species heterothallic Ascus elongates, with mating strains followed by many designated as a and α. mitotic divisions. Plasmogamy and Results in ascus karogamy of a and α with hundreds of mating strains forms ascospores Many zygote. instead of the mitotic typical eight. divisions Asci and ascospores are borne naked.
Saccharomyces cerevisiae Saccharomyces cerevisiae
Yeast cell budding: Ascus with four ascospores:
Ascus with ascospores
Filamentous Ascomycetes Filamentous Ascomycetes Introduction: Introduction (continued): Mycelium always septate, but septa Historically, classification of this incomplete, with pore in center. group has been based on the type Pore in septa often blocked in older of ascocarp produced. hyphae with woronin bodies. Molecular analyses has demonstrated this to be an artificial form of classification, but is still the most convenient means of classifying filamentous ascomycetes.
6 Filamentous Ascomycetes Filamentous Ascomycetes Introduction (continued): Cleistothecium: Asci and ascospores borne in an Ascocarp is entirely closed. ascocarp. Asci do not form a hymenium. Four types of ascocarps associated Usually member of Plectomycetes. with four informal categories of ascomycetes: Cleistothecium – Plectomycetes Perithecium – Pyrenomycetes Apothecium – Discomycetes Ascostroma - Loculoascomycetes
Filamentous Ascomycetes Filamentous Ascomycetes Perithecia: ¯Ostiole Apothecium: Commonly An ascocarp that flask- has its hymenium shaped. entirely open at Hymenium maturity. formed. Paraphyses Sterile filaments present: typically present. Paraphyses, periphyses and Discomycetes. pseudoparaphyses present or absent. Pyrenomycetes.
Filamentous Ascomycetes Ascocarp Development Ascostroma: Will use the development of Peziza as ascocarp wall absent representative of ascocarp (apothecium) development. Start at germination of ascospores to produce monokaryon. Monokaryons self sterile and cross fertile, i.e. heterothallic.
Cavity in a stroma where asci and ascospores are borne. Loculoascomycetes.
7 Ascocarp Development Monokaryon Strains
Each monokaryon have both ascogonia (female gametangia) and antheridia (male gametangia).
Ascocarp Development Ascocarp Development
Antheridial nuclei transported to the ascogonium through the trichogyne. Peziza The trichogyne is apothecium a tubular growth originating from the ascogonium. Ascocarp formed by tightly interwoven mycelium.
Ascocarp Development Ascocarp Development A1 and A2 nuclei Crozier Formation: pair off in ascogonium. Crozier A1 and A2 nuclei undergo Ascogenous synchronous hypha mitotic divisions. Ô Ascogenous hyphae (dikaryon) form from ascogonium.
8 Ascocarp Development Ascocarp Development Ascus Formation: Crozier Mitosis Ô Proliferation: Apical and Meiosis stalk cells Ô fuse. Karyogamy New crozier Ô proliferates. Crozier Crozier proliferation Ô occurs repeatedly.
Ascocarp Development Ascocarp Development Development of ascus and Ascogonium ascospores from forms asci, new crozier: ascospores and paraphyses: hymenium.
Ascocarp Development L-Sect.- Mature Apothecium
At same time ascus is developing, ascocarp is forming. Monokaryotic mycelium Í developes from stalk cell produce ascocarp.
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