Fungi (19) - Egan BISC-120

What two major groups make up unikonts?

amoebozoans which contain only protists

opisthokonts include the fungi and animal kingdoms plus some closely related protists

What are opisthokonts’ features and what groups does it consist of?

They are animals, fungi, and closely related protists. They propel with a singular posterior flagellate cell (think sperm for animals, spores of chytrid fungi)

What are fungi most closely relate to, and what is that group’s function?

nuclearlids; they are amoebas that feed on algae and bacteria

How are fungi characterized?

They are heterotrophic eukaryotes characterized by the absence of phagotrophy and the presence of a chitinous cell wall

What are fungi taxonomically?

monophyletic of nine major lineages

What’s the green hypothesis for fungal transition?

terrestrialization was dependent on terrestrialization in green plants

What’s the brown hypothesis for fungal transition?

zoosporic fungi acquired saprotrophic habits and colonized sediments or damp land — lost flagellum and developed hyphal morphology to complete transition

What’s the white hypothesis for fungal transition?

zoosporic fungi adapted to frozen environments that acted as an intermediate between aquatic and terrestrial environments

What do fungi use to break down complex molecules into smaller organic compounds, and what can they digest?

hydrolytic enzymes; these enzymes can digest compounds from a wide range of sources

Where is the fungal cell wall located?

outside the plasma membrane

What is the fungal cell wall composed of?

glucans, chitin, and glycoproteins

What are some common cell shapes for fungal cells?

spherical, ellipsoidal, cylindrical yeast cells

chains of highly polarized cylindrical cells which form pseudohyphae or hyphae

Some fungi are what?

dimorphic and hold more than one morphology, changing their appearance from environment.

How are hyphae divided in fungi?

hyphae are divided into cells by cross-walls, or septa. Septa have pores large enough to enable cell-to-cell movement of organelles

Hyphae are produced with unique cell types/cellular morphologies during what developmental processes?

• asexual and sexual reproduction

• pathogenesis for host penetration or host association during symbiosis

• proliferation in the environment for absorption

How do fungi propagate themselves?

They produce vast numbers of spores, either asexually or sexually

How do spores spread and germinate?

They are carried long distances by wind or water, and if they land in a most place with water, they will germinate

How do molds produce?

They produce haploid spores asexually by mitosis and form visible, “furry” mycelia

What is mycelium?

a vegetative part of a fungus, consisting of a network of fine, thread-like hyphae

Where do mycelium absorb and transport nutrients?

They absorb nutrients from its environment and transport them to where they are needed for growth and reproductions

Are fungal nuclei and spores diploid or haploid?

haploid

What does sexual reproduction in fungi require?

the fusion of hyphae from different mating types

What are pheromones, and how do fungi use them?

They are sexual signaling molecules and are used to communicate their mating type

What is plasmogamy?

the union of cytoplasm from two parent mycelia

What is a heterokaryon?

a mycelium that contains coexisting, genetically different nuclei

When a haploid nuclei pair off two to a cell, the mycelium is said to be what?

dikaryotic

What is karyogamy?

Karyogamy is the fusion of nuclei after the heterokaryotic stage

What happens after karyogamy?

1. the haploid nuclei fuse creating a diploid zygote cell

2. undergoes meiosis, producing haploid spores

How many known species of fungi exist within how many true phyla?

145,000 known species of fungi contained within five true phyla

How were the five phyla established?

according to their mode of sexual reproduction, with two other phyla that reproduce without a sexual cycle in a sixth basal group

What are cryptomycetes?

Cryptomycetes are found globally in soils, marine, and freshwater habitats; they are unicellular and have flagellated spores

What are microsporidians?

unicellular intracellular parasites of protists and animals; their spores infect host cells via a harpoon-like organelle (polar tubule)

What are chytridiomycota?

They are the simplest, most primitive true fungi featuring flagellated spores called zoospores; very similar to protists cell structure-wise

What is chytridiomycosis?

a fatal skin disease caused by chytrid fungal pathogens

What are zoopagomycota?

They form coenocytic hyphae and reproduce asexually via non-flagellated spores.

Zoopagomycetes that reproduce sexually form a structure called a zygosporangium.

What happens during plasmogamy?

Mating type mycelia meet and fuse [their cytoplasm], going into a dikaryotic state

• equivalent to sex

• sexual incompatibility is determined by molecular recognition mechanisms, controlled by a single mating-type locus

• fusion between mycelia of different mating types (plasmogamy) produces zygosporangium

After plasmogamy, what happens next?

They undergo karyogamy, where two nuclei fuse and undergo meiosis to produce spores

What are zygosporangia?

thick-walled structure, they are metabolically inactive and resistant to freezing and drying; when conditions improve, meiosis occurs and they germinate into sporangium

What is sporangium?

they develop at the tips of upright hyphae and function to release sporesÍ›

What are ascomycota?

they form septate hyphae with pores and vary in size and complexity

Why are ascomycetes often called sac fungi?

they have the saclike sci, which spores are produced.

What do ascomycetes produce during the sexual stage?

they produce fruiting bodies called ascocarps which contain the spore-forming asci

How do ascomycetes reproduce?

They reproduce asexually by enormous numbers of asexual spores called conidia produced at the tips of specialized hyphae called conidiophores

What is the cycle of events in ascomycete sexual reproduction?

1. mycelium from different mating types fuse 

2. dikaryotic cells formed: two haploid nuclei

3. asci form at the tips of dikaryotic hyphae, and karyogamy and meiosis occur within asci

4. ascospores develop and discharged from ascocarp

What are basiciomycota?

The phylum is defined by clublike structure called a basidium, a cell in which karyogamy and meiosis occur

What are examples of basidiomycetes?

mushrooms, puffballs, shelf fungi

How do basidiocarps reproduce sexually?

the mycelium produces fruiting bodies called basidiocarps

What is the life cycle of a basidiomycete?

1. they are long-lived dikaryotic mycelium

2. basidia experience karyogamy and are diploid nuclei

3. experience meiosis and basidium contain four haploid nuclei and four basidiospores, then disperse and germinate

What do saprotrophic fungi eat?

They break down and digest decayed (dead/waste) organic matter

What do parasitic fungi absorb?

they absorb nutrients from living hosts (in extreme cases they take over host motor functions)

What do mutualistic fungi absorb?

nutrients from hosts and reciprocate with actions that benefit the host

Why are fungi efficient decomposers?

they can decompose complex plant material such as lignin and cellulose

What are lichens?

symbiotic associations between photosynthetic microorganisms (cyanobacteria or algae) and fungi (mostly ascomycetes)

What are parasites?

a symbiont that consumes host resources (tissues, body fluids)

What is a pathogen?

A type of parasite that causes infectious disease