Introduction to Mycology & Kingdom of Fungi Lecture 1

Transcription

1 Introduction to Mycology & Kingdom of Fungi Lecture 1

2 What is a fungus? A eukaryotic, heterotrophic organism devoid of chlorophyll that obtains its nutrients by absorption, and reproduces by spores. The primary carbohydrate storage product of fungi is glycogen. Most fungi have a thallus composed of hyphae (sing. hypha) that elongate by tip growth

3 Fungal hyphae form a network called a mycelium (pl. mycelia)

4 Historical Perspective on classification of fungi Linnaeus Minerals exist; plants exist and live; animals exist, live and sense. Fungi are plants under this classification of organisms. Reflected in terminology: e.g, saprophytes (vs. saprotrophs)

5 Classification Whittaker (1969) proposed 5 kingdoms: Prokaryotes, Eukaryotes (Animals, Plants, Fungi, Protists) At least 7 kingdoms are now recognized: Eubacteria, Archaebacteria, Animalia, Plantae, Eumycota, Stramenopila (Chromista), Protoctista (Protozoa, Protista)

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7 Fungi versus fungi The small case fungus is used inclusively for a heterogenous group of organisms that have traditionally been studied by mycologists. Fungi refers to the organisms in the Kingdom Fungi, the true fungi, also called the Eumycota

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9 Kingdom Fungi Phyla: Chytridiomycota Zygomycota Ascomycota (inc.deuteromycetes) Basidiomycota

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11 Kingdom Stramenopila (Chromista) Phyla: Oomycota Hyphochytriomycota Labyrinthulomycota Protists (Protoctists) Phyla: Plasmodiophoromycota Dictyosteliomycota Acrasiomycota Myxomycota

12 How many species of fungi exist? Number described = 80,000 (+1,700 new species each year) Works on estimating fungi Hawksworth, D. L. (1991). The fungal dimension of biodiversity: magnitude, significance, and conservation. Mycological Research 95: Hawksworth, D.L. (2001) The magnitude of fungal diversity: the 1.5 million species estimate revisited. Mycological Research 105 (12):

13 Flowering plants on British Isles described = 2,000 species Fungi on British Isles described = 12,000 species Ratio of 6 fungi to each plant species Total number of described plant species = 250,000 (most plant species are believed to be described) 6 x 250,000=1.5 million species of fungi! Less than 5% of which are described, and at the current rate of description, it will take >800 years to describe all extant species.

14 Classification is the systematic arrangement of organisms into groups based on established criteria. Systematics is the study of the relationships and classification of the living world in a system or conceptual hierarchy. Taxonomy, nomenclature are subcategories of systematics. Taxonomy is the study of the theory, practice and rules of classification of living and extinct organisms. Nomenclature is the allocation of scientific names to the units a systematist considers to merit formal recognition. (Hawksworth et al., The Dictionary of the Fungi).

15 Nomenclature The nomenclature of fungi is governed by the International Code for Botanical Nomenclature, latest edition 1994, as adopted by the International Botanical Congress.

16 Nomenclature: Hierarchical Classification Kingdom Fungi Phylum Basidiomycota Class Basidiomycetes Order Agaricales Family Agaricaceae Genus Agaricus Species: Agaricus campestris L.

17 Agaricus campestris L. Agaricus campestris L. is the type species of the genus Agaricus L. campestris is the specific epithet Note that the genus and species are in italics (or underlined); the genus is capitalized, the species epithet is in lower case L. stands for Linnaeus, the authority

18 Agaricus bisporus (Lange) Imbach Lange and Imbach are the authorities for this species Lange was the first to describe this fungus, as Coprinus bisporus Imbach later transferred the species bisporus to the genus Agaricus

19 Authority the author of a scientific name of a taxon; the person/persons who formally described and published the name. What if there are several mycologists named Lange, how do we know which one did the work? Standard abbreviations of authority names can be found in the Dictionary of the Fungi (Hawksworth et al. 1995) and Fungi on Plants and Plant Products in the United States (Farr et al. 1989).

20 What is a species? Most fungi are morphospecies, or delimited on the basis of phenotype, most commonly by morphological characters. A biological species is a population, or a group of populations, among which there is interbreeding. Two individuals might not be able to interbreed, but they are still members of the same species (conspecific) if they are part of the same gene pool. ( Futuyma, D.J Evolutionary Biology).

21 What is a species? A phylogenetic species is irreducible (basal) cluster of organisms diagnosably different from other such clusters, and within which there is a parental pattern of ancestry and descent (Cracraft, J Speciation and Its Consequences).

22 For mycologists, species concepts and species recognition are problematic. John Taylor and colleagues have proposed a recognition concept that is rapidly gaining popularity among mycologists using a phylogenetic approach. This concept is termed Genealogical Concordance Phylogenetic Species Recognition (GCPSR) and encompasses a phylogenetic approach based on concordance (agreement) of multiple gene genealogies (Taylor et al., Fungal Genetics and Biology 31: 21-32).

23 Why study fungi? Fungi are among the most diverse organisms on Earth, and are considered only second to the Insects in species diversity.

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25 Associations Fungi are involved in symbiotic relationships with a number of organisms Lichens Mycorrhizas Endophytes Mutualists

26 Decomposers As saprotrophs, particularly as decomposers, fungi are essential components of the carbon cycle and are among the few organisms that can break down lignin

27 Pathogens Fungi are important as pathogens of animals and plants. Over 70% of all plant diseases are caused by fungi

28 Industrial applications Ethanol Brewing and baking Organic acids Citric acid for soft drinks Antibiotics Penicillin, griseofulvin, cyclosporin, etc. Enzymes Pectic enzymes, hemicellulase, etc.

29 Introduction to Kingdom Fungi

30 Modes of nutrition Fungi=absorptive heterotrophs Animals=phagotrophic heterotroph Heterotroph: an organism incapable of synthesizing carbohydrates from inorganic sources, and which must feed on organic materials produced by other organisms Plants=autotrophs

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

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34 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)

35 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) Sporopollenin (aromatic polymer found in spore walls of some fungi. Confers properties similar to melanin) Plasma membrane semi-permeable

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37 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.

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

39 Septal pores--ascomycota Woronin bodies

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

41 Fungal nuclei 1--3 µm diam chromosomes Up to 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)

42 Organism # bp # genes Escherichia coli 4,600, Saccharomyces cerevisiae 13,000, 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

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44 Fungal nuclei 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

45 Spindle Pole Body

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47 Other organelles Mitochondria flattened or plate-like mitochondrial cristae in Fungi Golgi bodies consist of a single cisternal element vs stacked cisternae Other types: ribosomes, endoplasmic reticulum, vacuoles, lipid bodies, glycogen storage particles, microbodies, microtubules, vesicles

48 Animal Cell Plant Cell

49 G. T. Cole Microbiol. Rev. 50:

50 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

51 Kingdom Fungi; Phyla Chytridiomycota Form motile spores called zoospores Meiosis occurs in resting sporangium 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

52 Concept of fungal holomorph Fungi may reproduce through asexual and/or sexual means 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

53 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)

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

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

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