Introduction to Kingdom Fungi

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

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

3. 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

4. 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

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

7. 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)

8. 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

10. 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.

11. Septal pores--Ascomycota • Woronin bodies

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

13. 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)

16. 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

17. 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

18. 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

19. 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

20. Spindle Pole Body

22. 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

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

24. Animal Cell Plant Cell

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

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

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

28. Kingdom Fungi • Phyla: • Chytridiomycota • 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

29. 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

30. 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)

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

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

35. 2n n Meiosis n n + n Plasmogamy Fungal life cycles mitosis Life cycle is predominantly diploid (2n) n + n 2n Karyogamy