Introductory Mycology Cell Structures What are fungi Eukaryotic

Introductory Mycology – Cell Structures

What are fungi? • Eukaryotic, spore-bearing, heterotrophic organisms that produce extracellular enzymes and absorb their nutrition.

Body Plan • unicellular (yeast), filamentous, or both (=dimorphic) • Hypha (pl. hyphae) is the basic “cellular” unit in filamentous fungi; they may be septate or coenocytic (aseptate); collectively a mycelium • limited tissue differentiation and division of labor • somatic & reproductive structures • plectenchyma: all organized fungal tissue, somatic & reproductive

Fungal nuclei • 1 --3 m diam • 3 --40 chromosomes • Up to 13 --40 Mb (million base pairs) DNA coding for 6, 000 to 13, 000 genes • Intranuclear division--nuclear envelope remains intact during mitosis (unlike plants and animals)

Organism Escherichia coli Saccharomyces cerevisiae # bp # genes 4, 600, 000 4288 13, 000 5885 Caenorhabditis elegans ~100, 000 ~14, 000 Arabidopsis thaliana ~120, 000 ~10, 000 Drosophila melanogaster ~170, 000 ~12, 000 ~3, 400, 000 ~80, 000 humans

Fungi as model organisms • Small genome relative to other eukaryotes • Many fungal genes are homologous to those in other eukaryotes • Easy to grow, short life cycles • Haploid genomes amenable to mutation • Sexual stage for analysis of segregation and recombination of genes; all products of meiosis can be retrieved in haploid spores • Asexual (clonal) reproduction

Beadle and Tatum Using the common bread mold Neurospora crassa, in 1941 developed the classic concept of “one gene, one enzyme” Awarded Nobel Prize in 1945

Nuclear Status • Eukaryotic; uni, bi- or multinucleate • Haploid, diploid (less frequent) • Monokaryon (1 nucleus per hyphal compartment) • Dikaryon (2 nuclei per hyphal compartment) • Homokaryotic • Heterokaryotic

• Mitosis – intranuclear: nuclear membrane doesn't breakdown during mitosis – centric in flagellated forms; typical centrioles of eukaryotes – noncentric in nonflagellated forms; possess spindle pole bodies (SPBs); differ from centrioles in lacking microtubular component

• • • Organelles typical eukaryote assemblage of organelles + fungal specific ones mitochondria endoplasmic reticulum Golgi equivalents single cisternal elements vacuoles microbodies funx in fatty acid degradation, N metabolism

Other organelles • Mitochondria—flattened or plate-like mitochondrial cristae in Fungi (similar to animals) • Golgi bodies—consist of a single, tubular cisternal element (stacked, plate-like cisternae in animals and plants) • Other types: – ribosomes, endoplasmic reticulum, vacuoles, lipid bodies, glycogen storage particles, microbodies, microtubules, vesicles

Cell Wall Chitin • well defined • chitin 1 -4 n-acetyal glucosamine • -glucans Cellulose polymers of glucose 1 -3 glucose • cellulose in some 1 -4 glucose 1 -3 glucan chitin -glucans

Fungal cell wall composition Structural components: chitin microfibrils [ß(1 -4)-linked polymer of N-acetylglucosamine] chitosan in Zygomycota [ß(1 -4)-linked polymer of glucosamine] ß-linked glucans Gel-like components: Mannoproteins (form matrix throughout wall

Other cell wall components Antigenic glycoproteins, agglutinans, adhesions— on cell wall surface Melanins—dark brown to black pigments (confer resistance to enzyme lysis, confer mechanical strength and protect cells from UV light, solar radiation and desiccation) Plasma membrane—semi-permeable

• fungal specific organelles involved in cell wall growth Spitzenkorper or vacuole associated with growing hyphal tips in septate fungi chitosome microvesicles transporting chitin synthases to growing cell wall

Nutrition • • • Heterotrophic Secrete extracellular enzymes Absorptive nutrition Saprobes: decay dead organic matter pathogens: biotroph, necrotroph symbionts: parasites - commensals - mutualists

Spores - a minute propagative unit functioning as a seed, but differing from it in that a spore does not contain a preformed embryo Fruiting body - any complex fungal structure that contains or bears spores; a sporocarp

Reproduction • Sexual reproduction: spores meiotically derived nuclei • Homothallic (selfing) • Heterothallic (outcrossing) • Genetic mating system – MAT loci – 1 to hundreds of “sexes” • Asexual reproduction – Spores with mitotically derived nuclei

Fungal Reproduction • Many fungi have the ability to reproduce by asexual and sexual means

Asexual Reproduction in Fungi • Fragmentation – hyphae simply break off. • Budding – small outgrowth of hyphae pinches off • Formation of spores – Sporangiospores: produced in sporangia (sac-like structures) located on a sporangiophore. – Conidiospores: produced at the tips of specialized hyphae

Fungal reproduction • Anamorph= asexual stage – Mitospore=spore formed via asexual reproduction (mitosis), commonly called a conidium or sporangiospore • Teleomorph= sexual stage – Meiospore=spore formed via sexual reproduction (e. g. , resulting from meiosis), type of spore varies by phylum

Kingdom Fungi • Phyla: – Zygomycota • Form asexual spores called sporangiospores • Meiosis occurs in zygospore – Ascomycota (including Deuteromycetes) • Form asexual spores called conidia • Meiosis occurs in ascus – Basidiomycota • Meiosis occurs in basidium

Fungal life cycles • The vegetative thallus predominates in the life cycle of a fungus • The thallus may be haploid (1 n), dikaryotic (n+n) or diploid (2 n) in different groups of fungi • Ploidy of thallus is determined by the timing of these events in the life cycle: – Plasmogamy (cell fusion) – Karyogamy (nuclear fusion) – Meiosis (reduction division)

Misc. • Life cycle: simple to complex; wide variety • Sporocarps: microscopic or macroscopic, limited tissue differientiation • Habitat: ubiquitous • Studied by mycologists!!!!!!

Fungal life cycles mitosis Life cycle is predominantly haploid (n) n n+n Plasmogamy n+n 2 n 2 n n Meiosis Karyogamy

Fungal life cycles mitosis Life cycle is predominantly dikaryotic (n + n) n + n 2 n Karyogamy 2 n n + n Plasmogamy Meiosis

Fungal life cycles mitosis Life cycle is predominantly diploid (2 n) 2 n n Meiosis n n + n 2 n Karyogamy Plasmogamy

What are fungi? • Eukaryotic, spore-bearing, heterotrophic organisms that produce extracelluar enzymes and absorb their nutrition.

Fungi vs. "fungi" • Based on the phenotypic definitions or traits attributed to fungi, fungi do not comprise a single monophyletic group of organisms • more than one evolutionary origin • not all "fungi" are members of the Kingdom Fungi

Some characters that separate the Kingdom Fungi from “protistan fungi” Kingdom Fungi Protistan fungi mitochondria: cristae flattened cristae tubular motile cells: motile cells with anterior or lateral heterokont flagella no motile cells or posterior flagellum cell wall carbohydrate: glucans, chitin lysine biosynthesis: alpha-aminoadepic acid (AAA) glucans, cellulose diaminopimelic (DAP) storage compound glycogen mycolaminarins sterols ergosterol fucosterol Phyla: (emphasized in class) Chytridiomycota Zygomycota Glomeromycota Basidiomycota Ascomycota Oomycota Myxomycota Dictyosteliomycota

General characteristics of the Phyla of the Kingdom Fungi basal lineages Zygomycota: (1000) • generally coenocytic mycelium • production of zygosporangia & zygospores • no sporocarp production

Basidiomycota: (22500) • septate mycelium • clamp connections • complex dolipore septa • dikaryotic, haploid mycelium • production of exospores (basidiospores) on a basidium • production of complex sporocarps Ascomycota: (35000) • septate mycelium • simple septa • monokaryotic, haploid mycelium • production of endospores (ascospores) in an ascus • production of complex sporocarps • often dominant asexual reproduction

Nomenclature Amanita muscaria Kingdom - Fungi Phylum - Basidiomycota Class - Hymenomycetes Order - Agaricales Family - Amanitaceae Genus - Amanita Species - A. muscaria

Medically important fungi are in four phyla: 1. Ascomycota - Sexual reproduction in a sack called an ascus with the production of ascopspores. ( Aspergillus, Blastomyces dermatidis, Histoplasma capsulatus) 2. Basidiomycota -Sexual reproduction in a sack called a basidium with the production of basidiospores. ( Cryptococcus neoformans) 3. Zygomycota - sexual reproduction by gametes and asexual reproduction with the formation of zygospores. ( Rhizopus, Mucor) 4. Deuteromycota(Fungi Imperfecti Mitosporic Fungi) - no recognizable form of sexual reproduction. Includes most pathogenic fungi ( Sporothrix, Coccidioides immitis, Candida, Pneumocystis).

Introductory Mycology- Cell Structure