Introduction to Kingdom Fungi Pl P 421/521 General Mycology LECTURE 2

What is a fungus? A eukaryotic, heterotrophic organism devoid of chlorophyll that obtains its nutrients by absorption, and reproduces by spores.

Modes of nutrition Fungi=absorptive heterotrophs Animals=phagotrophic heterotroph Heterotroph (chemo-organotrophs): an organism incapable of synthesizing carbohydrates from inorganic sources; requires preformed organic compounds produced by other organisms Plants=autotrophs

Hyphae (singular, hypha) Cylindrical, branching filaments composed of a tubular cell wall filled with cytoplasm and organelles Most fungal hyphae are 2-10 m diameter

http://www.uoguelph.ca/~gbarron/MISCELLANEOUS/hairpen.htm

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

Septa Septa—regular cross-walls formed in hyphae. Hyphae with septa are septate, those lacking septa except to delimit reproductive structures and aging hyphae are called aseptate or coenocytic. primary septa are formed as a process of hyphal extension and generally have a septal pore, which allows for cytoplasmic and organelle movement. Secondary or adventitious septa are imperforate, formed to wall off ageing parts of the mycelium.

Kingdom Fungi Chytridiomycota—lack true hyphae Zygomycota—coenocytic hyphae Glomeromycota—coenocytic hyphae Ascomycota—septate hyphae Simple septa, Woronin bodies Basidiomycota—septate hyphae Dolipore septa, parenthesomes

Septal pores--Ascomycota Woronin bodies

Septal pores--Basidiomycota Dolipore septa, septal pore caps or parenthosomes Septal pore cap

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

“Unikont”—eukaryotic cell with one flagellum Tree of eukaryotes, showing variation in genome size. From Keeling and Slamovits (2005). Current Opinion in Genetics and Development 15: 601-608 “Unikont”—eukaryotic cell with one flagellum

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

Fungal nuclei Usually haploid Nuclear membrane persists during division Nuclear associated organelles (NAOs): Associated with the nuclear envelope; function as microtubule-organizing centers during mitosis and meiosis Spindle pole bodies In fungi that lack a flagellated stage in lifecycle Centrioles In fungi and other organisms possessing flagellated stage in lifecycle

Spindle Pole Body

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

Storage Compounds Glycogen, lipids and trehalose in fungi and animals Starch in plants

Animal Cell Plant Cell

G. T. Cole. 1986. Microbiol. Rev. 50: 95-132

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

Fungal reproduction Anamorph= asexual stage Teleomorph= sexual 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: Chytridiomycota Glomeromycota Zygomycota Form motile spores called zoospores Meiosis occurs in resting sporangium Glomeromycota Form spores containing hundreds of nuclei; no known sexual reproduction 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

Concept of fungal holomorph Asexual and sexual reproduction may be separated in time and space The holomorph is the entire fungus—including asexual and sexual stages if both are formed

Fungal life cycles The vegetative thallus predominates in the life cycle of a fungus The thallus may be haploid (1n), dikaryotic (n+n) or diploid (2n) 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)

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

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

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