Introduction to Fungi Flashcards
Opisthokonts
Cells, when flagellate, possess a single posterior flagellum
How many species of fungi are bioluminescent
> 70
Are fungi usually haploid or diploid?
Haploid
Describe fungal cell walls
- Contain glucans (plant) and chitin (arthropod exoskeleton)
- rigid
- unique composition
What links fungi with oomycetes?
Hyphae
Describe hyphae
- filamentous growth structures
- grow at the tip
Describe dimorphic fungi
Can switch between yeast and hyphal forms in response to their environment
How do unicellular years reproduce?
Budding or fission
Describe the current fungal phyla
- 8 phyla
- 12 subphyla
- 46 classes
Describe microsporidia
Intracellular parasites of all groups of animals
Describe chytridiomycota
- flagellated
- motile zoospores
- common in aquatic environments
Describe neocallimastigomycetes
Anaerobes found in the rumen and hindgut of herbivores
Describe zoopagomhcota
Pathogens and commensale of animals, rarely plants
Describe mycoromycota
- mostly associations with pants
- subphylum Glomeromycota
Describe Glomeromycota
Have arbuscular mycorrhizae
Describe ascomycota
Diverse - include yeasts and common moulds such as Aspergillus
Basidiomycota
- mushrooms and toadstools
- rusts and smuts
- septal pore swelling (regulates cytoplasmic streaming, restricts nuclear/organelle movement)
How many fungal species are there?
2.2-3.8 mill
How many fungal
Species are currently
Accepted?
120,000
Describe Esher common
- 3,400 fungal sp
- 420 vascular plant sp
- 8:1
Describe slapton ley
- 1,136 fungal sp
- 88 vascular plant sp
- 12.9:1
What percentage of known fungal species are marine?
<1%
What percentage of terrestrial plants depend on mycorrhizal fungi?
- 95%
How many species of mycorrhizal fungi are there?
~6000
Laccases
Modification of lignin
What makes fungal absorption efficient?
High SA:Vol
What does absorption probably constrain wrt fungi?
Hyphal diameter (not hyphal length)
Basidiomycota
Lignin degradation (the only organisms that can do it)
Give an example of saprophytic fungi
Wood rotting fungi
Give examples of symbiotic fungi
- Mycorrhizae
- Lichens
Give examples of mycoses
- Athletes food (human)
- Chytridiomycosis (frogs)
- What stem rust (plants)
How big is a yeast cell?
3-4μm
How big is a hyphae?
2-10μm
Describe Armillaria ostoyae
- humongous fungus
- largest living organism
- 10km SA
- 8500years old
Rhizomorph
- Multiple hyphae oriented in parallel
- transport nutrients long distances
Why does the fungal cell wall need to withstand high turgour pressure?
Growing hyphae
Cell wall importance
- Determines shape
- Provides protection
- Site of nutrient exchange
What does the fungal lipid bilayer contain?
Ergosterol
What does septa compartmentalisation provide fungi?
- mechanical strength
- isolation of damaged/aging hyphae
- differentiation (sporulation)
Describe Zygomycetes
- Aseptate
- Woronin body allows cytoplasmic streaming and nuclear/organelle movement
Hyphae without septa are
- Coenocytic
- have multiple nuclei
What allows hyphal branching?
lots of cytoplasmic streaming
Describe Dikarya
Growth direction is enabled and defined by Spitzenkörper
Mycelium
Complex 3D networks of hyphae
Describe the growth of a he inner region of mycelium
- denser, fused hyphae
- branching/infilling
- positive autotropy and anastomosis
- good connectivity for transport
Describe regulation of mycelium growth in the outer region
- sparser, unbranched hyphae (exploratory)
- negative autotropy (good space-filling)
Branching frequency and fungal foraging
- sensitive to environmental conditions
- more exploratory hyphae occur under nutrient stress
- more dense colonies occur under nutrient excess
Autotropism
Sensing of neighbouring hyphae via O2 or CO2 concentrations followed by growth towards (+ve) it away (-ve) from neighbours
Describe fungal growth on agar
Gives rise to radial colonies on rich media
Give a yeast that undergoes budding
Saccharomyces cerevisiae
Give a yeast that undergoes fission
Saccharomyces pombe
Give an example of a dimorphic fungus
- Candida albicans
- filamentous or unicellular depending in environment
Give examples of asexual fungal clades
- Chytridiomycota
- Penicillum
How do fungal spores form
- Fusion of unicellular gametes/specialised hyphae
- Fusion of 2 haploid cells to form a diploid cell, which undergoes meiosis and mitosis
Ascospores
Occur in a sac
Describe fungal sexual spores
resistant to drying, heat, freezing, and some chemicals
Homokaryon
Coenocytic hyphae (many identical nuclei in the same piece of cytoplasm)
What does coenocytism provide
Local complémentation
Anastomosis
- Fusion between branches of same or different hyphae
- promiscuous (little control)
What does the phenotype of a fungus depend on?
Interactions between genetically varying nuclei in the cytoplasm
Describe spatially dependent phenotypes wrt fungi
Mycelium phenotype is different in different parts
What is the advantages of heterokaryon?
- Greater physiological flexibility to react to different nutritional environments
- increase genetic diversity without need for sexual reproduction
- can grow on minimal medium
Heterokaryon
- two auxotrophs (lys) and (ade-) jointly can synthesise joth amino acids
- nuclei remain unfused
- local phenotype
Fusions might occur
- tip-to-tip
- tip-to-side
- side-to-side (tip induction and outgrowth of peg-like branches)
Describe vegetative compatibility genes
- v-c genes
- determine if fusion is maintained or shorter
What causes vegetative incompatibility
Genetic differences at het loci
Het
Heterokaryon
What does vegetative incompatibility result in?
Death of fused cells (apoptosis)
Stable heterokaryons do not guarantee
Sexual reproduction
Barrage
Line of dead cells following fusion
Plasmogamy
Fusing of cytoplasm of two cells
Karyogamy
Fusing of nucleus of two cells
Homothallic
Self-fertile
Heterothallic
Require compatible mating types
Describe the pathway of fungal sexual reproduction
- Anastomosis
- Plasmogamy
- Karyogamy
- Meiosis
Anamorph
- Asexual reproductive stage
- mould like
Teleomorph
- sexual reproductive stage
- fruiting body
Holomorph
- whole fungus
- anamorph and teleomorph
Arbuscular mycorrhizae
- non-woody plants
- grow within root cells to form arbuscles
- obligate biotroph
- e.g. Glomeromycota
Arbuscles
Site of nutrient exchange
Ectomycorhiza
- woody trees/shrubs
- Hartig net
- wood wide web
Hartig net
- sheath formed around plant root structure
- hyphae penetrate outer root cell layer
- allows nutrient exchange
Benefits of mycorrhizae to the plant
- increased nutrient uptake (increased SA, nutrient mobilisation and scavenging efficiency)
- tolerance to water stress and pathogens
- phosphate solubilisation
- ammonium absorption
Benefits of mycorrhizzae to the fungus
- 10-20% photosynthates go to the fungus
- reciprocal relationship (the more photosynthate to the fungus, the more nutrients to the plant)
Describe lichens
Ascomycota with phototrophic partner
What are the potential phototrophic partners in lichens?
photosynthetic alga, Cyanobacteria or basidiomycete
What do the symbionts provide in lichen?
- phototrophic partner provides organic carbon
- fungus provided weather protection and promotes rock inorganic nutrient use
Heterokonts
More than one flagella, often at front of cell
What makes fungal classification elusive?
Morphotypes
What is the oldest part of a mycelial colony?
The spores in the middle
The outside of a mycelial colony will grow
Continuously
Homokaryon and heterokaryon
- occupy different areas
- have the same phenotype
