Fungi Chapter 31 Defining Fungi Mycologists believe there

Fungi Chapter 31

Defining Fungi Mycologists believe there may be as many as 1. 5 million fungal species Fungi are classified into six main groups -Chytrids -Zygomycetes -Glomeromycetes -Ascomycetes -Basidiomycetes -Deuteromycetes 2

Defining Fungi 3

Defining Fungi (Cont. ) 4

Defining Fungi share the following characteristics 1. Are heterotrophs that absorb nutrients 2. Have a number of different cell types 3. Have cell walls that include chitin 4. Some have a dikaryon stage 5. Undergo nuclear mitosis 5

General Biology of the Fungi Multicellular fungi consist of long, slender filaments called hyphae -Some hyphae are continuous -Others are divided by septa 6

General Biology of the Fungi A mass of connected hyphae is called a mycelium -It grows through and digests its substrate 7

General Biology of the Fungi Cells walls of fungi are formed of polysaccharides including chitin -Cross-linked with proteins Chitin is also found in the hard shells (exoskeletons) of arthropods 8

General Biology of the Fungi Hyphae may have more than one nucleus -Monokaryotic – One nucleus -Dikaryotic – Two nuclei Sometimes many nuclei intermingle in the common cytoplasm of the fungal mycelium -Heterokaryotic – Nuclei from genetically distinct individuals -Homokaryotic – Nuclei are genetically similar to one another 9

General Biology of the Fungi have an unusual mitosis -Nucleus does not break down and reform Fungi lack centrioles -Instead, they have small, amorphous structures termed spindle plaques -These form the spindle apparatus within the nucleus 10

General Biology of the Fungi can reproduce sexually and asexually Sexual reproduction involves the fusion of two haploid hyphae of compatible mating types this is fertilization or plasmogamy -In some fungi, fusion immediately results in a diploid (2 n) cell -Others, have a dikaryotic stage (1 n + 1 n) before parental nuclei form diploid nucleus 11

General Biology of the Fungi Spores are the most common means of reproduction among fungi -May form from sexual or asexual processes -Most are dispersed by wind -Some by insects or small animals Chytrids are the only group to retain ancestral flagella and have motile zoospores 12

General Biology of the Fungi 13

General Biology of the Fungi obtain food by secreting digestive enzymes into their substrates -They then absorb the organic molecules produced by this external digestion Fungi can break down cellulose and lignin Some fungi are carnivorous 14

General Biology of the Fungi 15

General Biology of the Fungi (Cont. ) 16

Phylogenetic Relationships There are five major fungal phyla -Based on mode of sexual reproduction 17

Phylogenetic Relationships Increasing molecular sequence data suggest that fungi are more closely related to animals than to plants The Glomeromycota, Ascomycota and Basidiomycota are monophyletic -Other two phyla are not The phylogeny of Deuteromycota is yet to be determined 18

Chytridiomycetes or chytrids are members of the phylum Chytridiomycota -Most closely related to ancestral fungi -Only fungi with flagellated spores -Have chitin in their cell walls -Life cycle has both haploid and diploid multicellular stages 19

Chytridiomycetes 20

Zygomycetes (phylum Zygomycota) are incredibly diverse -Include the common bread molds -And a few human pathogens -Lack septa in their hyphae except when they are reproducing 21

Zygomycetes Sexual reproduction begins with the fusion of gametangia, which contain numerous nuclei -A zygosporangium is produced, within which a zygospore develops Asexual reproduction occurs much more frequently -Hyphae produce clumps of erect stalks, called sporangiophores -Tips form sporangia with spores 22

Zygomycetes 23

Glomeromycetes (phylum Glomeromycota) are a tiny group of monophyletic fungi -They form intracellular associations with plant roots called arbuscular mycorrhizae -They show no evidence of sexual reproduction 24

Ascomycetes (phylum Ascomycota) contain about 75% of the known fungi -Include bread yeasts, common molds and many serious plant pathogens -Also cup fungi and morels 25

Ascomycetes are named for their reproductive structure: a microscopic, saclike ascus Asci form within the ascocarp Karyogamy occurs within asci Meiosis and mitosis follow, producing 8 haploid nuclei that become walled ascospores 26

Ascomycetes Asexual reproduction is very common -Occurs through conidia formed at the ends of modified hyphae called conidiophores -Many conidia are multinucleate 27

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Ascomycetes Yeasts are unicellular ascomycetes -Most reproduce asexually by budding Yeasts can ferment carbohydrates -Break down glucose into ethanol and CO 2 -Used to make bread, beer and wine -Saccharomyces cerevisiae 29

Ascomycetes Yeasts have become increasingly important in genetic research -Yeast artificial chromosomes (YACs) -Yeast two-hybrid system -Fungal genome initiative 30

Basidiomycetes (phylum Basidiomycota) include some of the most familiar fungi -Mushrooms, puffballs, jelly fungi -Plant pathogens such as rusts and smuts 31

Basidiomycetes are named for their sexual reproductive structure, the club-shaped basidium Karyogamy occurs within basidia Meiosis follows The four haploid products are incorporated into basidiospores, which are borne externally 32

Basidiomycetes Spore germination leads to the production of monokaryotic hyphae -This results in a monokaryotic mycelium, or primary mycelium Different mating types of monokaryotic hyphae may fuse -This results in a dikaryotic mycelium, or secondary mycelium The basidiocarps (mushrooms) are formed entirely of secondary mycelium 33

Basidiomycetes 34

Deuteromycetes, formerly called imperfect fungi, are a polyphyletic group -There about 15, 000 species -No sexual reproductive stage has been observed -Many appear to be related to the ascomycetes 35

Deuteromycetes Hyphae of different types fuse spontaneously to produce heterokaryotic hyphae -These exhibit a special kind of genetic recombination called parasexuality -Genetically distinct nuclei exchange portions of chromosomes Parasexuality also occurs in other fungi 36

Deuteromycetes Include economically important molds -Penicillium -Penicillin -Blue cheeses -Aspergillus -Soy sauce -Soy paste 37

Ecology of Fungi, together with bacteria are the principal decomposers in the biosphere Fungi are virtually the only organisms capable of breaking down cellulose and lignin Fungi have entered into fascinating symbioses with a variety of life forms -Obligate symbiosis – Essential for fungus survival -Facultative symbiosis – Nonessential 38

Ecology of Fungi Types of symbioses -Pathogens and parasites benefit at the expense of their host -Commensals benefit one partner but do not harm or benefit the other -Mutualistic relationships benefit both partners 39

Ecology of Fungi Endophytic fungi live in the intercellular spaces inside plants -Some fungi protect their hosts from herbivores by producing toxins -Italian rye grass is more resistant to aphid feeding in the presence of endophytes 40

Ecology of Fungi 41

Ecology of Fungi (Cont. ) 42

Ecology of Fungi Lichens are symbiotic associations between a fungus and a photosynthetic partner -Ascomycetes are found in all but about 20 of the 15, 000 lichen species 43

Ecology of Fungi Lichens have invaded the harshest habitats, where they are often the first colonists Lichens have pigments 44

Ecology of Fungi (Cont. ) Lichens are used as bioindicators of air quality 45

Ecology of Fungi Mycorrhizae are mutualistic relationships between fungi and plants -Found on the roots of about 90% of all known vascular plant species -Two principal types 46

Ecology of Fungi Arbuscular mycorrhizae -Hyphae penetrate the root cell wall -By far the most common (70% of all species) -Fungal partners are Glomeromycetes Ectomycorrhizae -Hyphae surround but do not penetrate the root cells -Most hosts are forest trees (pines, oaks) -Fungal partners are mostly Basidiomycetes 47

Ecology of Fungi 48

Ecology of Fungi (Cont. ) 49

Ecology of Fungi also form mutual symbioses with animals -Ruminant animals host fungi in their gut -Leaf-cutter Attini ants have domesticated fungi which they keep in underground garden 50

Fungal Parasites and Pathogens Fungal species cause many diseases in plants -Armillaria has damaged large regions of coniferous forests 51

Fungal Parasites and Pathogens 52

Fungal Parasites and Pathogens (Cont. ) 53

Fungal Parasites and Pathogens Fungi can also spoil food products that have been harvested and stored Some fungi secrete toxins that make foods poisonous -Fusarium – Vomitoxin -Aspergillus flavus - Aflatoxin 54

Fungal Parasites and Pathogens 55

Fungal Parasites and Pathogens Fungi also cause human and animal diseases -Candida – Thrush; vaginal infections -Pneumocystis jiroveci – Pneumonia -Athlete’s foot and nail fungus Fungal diseases are difficult to treat because of the close phylogenetic relationship between fungi and animals 56

Fungal Parasites and Pathogens Batrachochytrium dendrobatidis causes chitridiomycosis -Responsible for the worldwide decline in amphibian populations 57