MYCO | 1.5 Fungal Spores: Structure, Dormancy, & Dispersal

Spores are microscopic propagules of _ that lack an embryo and are specialized for _

• great structural and size diversity

• dispersal (space) and dormant survival (time)

_ is a cell capable of growing into the same organism as the spore came from

Propagule

T/F: All fungal spores are unicellular

FALSE

Fungal spores can be uni- or multicellular

Enumerate functions of spores

• Sexually produced spores = dormant survival

• Asexual spores (conidia) = dispersal (short- or long-range)

• Chlamydospores = specialized thick-walled spores that develop from hypha during nutrient stress

Explain convention for naming spores

• Spores are usually named after the division that produced them, e.g., Ascomycota = ascospores; Basidiomycota = basidiospores

• Some are named after their origin, e.g., mitospores = produced by mitosis

Enumerate differences between fungal spore vs. average somatic fungal cell

• Wall is thicker = additional layers or pigments

• Internal structures = cytoplasm is dense, organelles (e.g., ER) are underdeveloped

  • Mostly ribosomes

• Low water content, respiration rate, and production of nucleic acids and proteins (dormant)

• High energy storage material = lipids, glycogen, trehalose lgt

• Ploidy = asexual spores are haploid

Enumerate common forms of fungal spores + expectations from their design

• Sexually-derived multicellular ascospores package meiotically derived nuclei

• Appendaged spores allow adhesion to many surfaces

  • Not just terrestrial but also an aquatic environment adaptation

  • Controls how fast they’re taken by water

• Glass asexual macroconidia use quick methods of short-distance dispersal

• Multiple conidia produced in great numbers allow faster colonization of environments

Spore common form

• _ package meiotically derived nuclei

Sexually-derived multicellular ascospores

Spore common form

• _ are used as quick methods for short-distance dispersal

Glass asexual macroconidia (not actual glass, just transparent hence glass = hyaline)

Spore common form

• _ allow adhesion to many types of surfaces

Appendaged spores

Spore common form

• _ allow fast colonization of environments

Multiple conidia produced in great numbers

T/F: There is massive diversity of spore structural adaptation to their target environments

TRUE

Enumerate structural variations observed in fungal spores

• Caryospora ascospores = 2 beauty blender; colorless septate end cells

• Choiromyces ascospores = ragadaga; peg-like ornamentations on spore surface

• Curvularia conidia = croissant worm; 4 transverse septa unequal and thus curved; conspicuous basal attachment scar at 1 end

• Melanospora ascoposores = lemon-shaped with apical pores at each end

  • Usually fungi only have 1 pore

• Microthyrium = shield-like sporophore called thyrothecium made up several spores fused together

  • Wind- and water-dispersed

• Pestalotiopsis conidia = gummy cola; 3 brown central cells + collapsing colorless appendage cells at end

• Testudina ascospores = honeycomb-like surface ornamentation

• Thecaphora spores = spore balls w/ cell tetrads that have spiny surface

• Thermomyces conidia = Ferrero rocher; coarsely-warted external cell walls

• Ustilago single-celled spores = distinct surface-like projections
  
  *Conidia = Curvularia, Pestalotiopsis, Thermomyces

Some fungi produce _ to enhance their survival, e.g., Fusarium oxysporum macroconidia, microconidia, and chlamydospores

multiple types of spores

T/F: Exogenously-imposed dormancy is often found in sexual spores, while constitutive dormancy is often found in asexual spores

FALSE

Exogenously-imposed dormancy is often found in asexual spores (conidia), while constitutive dormancy is often found in sexual spores (ascospores)

In _ dormancy, _ spores would remain dormant in environments unsuitable for growth but would germinate readily in favorable settings

• Exogenously-imposed dormancy

• Asexual

• e.g., Talaromyces atroroseus

In _ dormancy, _ spores would not germinate readily in favorable settings but would require post-maturation or specific activation trigger

• Constitutive

• Sexual

• e.g., Lyophyllum decastes

3 types of spores produced by Fusarium oxysporum, which is the causative agent of Fusarium wilt disease

Macroconidia, microconidia, chlamydospores

T/F: In some fungi, conidia can develop from fragmented hyphae without needing a conidiophore

TRUE

_ is the primary cause of wilting symptoms in plants infected by Fusarium oxysporum

Blockage of xylem by mycelia

All fungal spores can be classified into two, namely _, based on their germination triggers

• Exogenously-imposed dormancy

• Constitutive dormancy

T/F: Almost all fungal spores are dormant since their metabolic rate is high

FALSE

Almost all fungal spores are dormant since their metabolic rate is low

All germinating fungal spores follow a _

common pattern of initial development

3 basic patterns in initial development of germinating spores

1. Isotropic growth = hydration, increase in size and metabolic activity

2. Hyphal emergence = emergence of germ tube

3. Hyphal growth = produce hyphae, or in some cases, microcycle sporulation

_ are specialized thick-walled spores that develop from hypha during nutrient stress

Chlamydospores

_ can be triggered by many factors reflecting ecology of fungus

Constitutive dormancy

Constitutive dormancy has been linked to several factors, including _, but is poorly understood

(what triggers spore activation from c dormancy) phar

• Post-maturation: CW dissolution, thinning

• Heat, cold, chemical exposure

• Ability to utilize enzymes to metabolize energy reserves, e.g., trehalase

• Removal of inhibitors after dispersal

T/F: In very rare cases, plant host metabolites can trigger germination of sexual spores

FALSE

In very rare cases, plant host metabolites can trigger germination of asexual spores

• The ecological significance of constitutive dormancy is that, often, _

• Enumerate 3 common types of triggers for activation from constitutive dormancy

• Triggers for germination is dependent upon reproductive or dispersal behavior of fungal spore

• 3 triggers for activation

  • Coprophilous = triggered by acidic environment

    • e.g., Bolbitius is activated in lab by treatment at 37 C in acidic conditions, simulating gut envi

  • Thermophilic = triggered by heating or warm ash

    • e.g., Neurosporea is triggered by temp at 60 C or above; dormancy is due to inability to utilize enzymes for metabolizing trehalose

  • Association = triggered by compounds released when close to parent hyphae

_ ends fungistasis in dormant asexual spores

Availability of nutrients

Asexual spores can be held in suppressed state of dormancy called _ in natural habitats

Fungistasis or mycostasis

_ is a microbially induced suppression of spore germination caused by nutrient competition or microbial metabolites or both but not by antibiotics or inhibitors from other microbes

Fungistasis or Mycostasis

2 causes of mycostasis

• Nutrient competition

• Microbial metabolites (produced by competitors)

In natural soil, microbial activity contributes to spore dormancy by _

depleting nutrients and producing growth inhibitors

T/F: Fungal spores differ from average somatic fungal cell such that asexual spores are diploid

FALSE

Fungal spores differ from average somatic fungal cell such that asexual spores are haploid

Fungistasis causes spores to remain quiescent in soil or natural habitats until _

• Nutrients become available or

• Other microbes decline

In very rare cases, _ can trigger germination of asexual spores

plant host metabolites

Explain recent evidence of host-specific triggering of germination in asexual spores (exogenously-imposed dormancy)

• In very rare case, there is evidence of host-specific triggering of germination

  • Sclerotia of Sclerotium cepivorum (which cases economically important “white rot” disease in onions and garlic) have volatile chemical germination triggers

• So what happens is,

  • Onions release nonvolatile sulfur compounds

  • But, soil bacteria converts these nonvolatile S compounds into volatile compounds

  • Volatile compounds then trigger the germination of Sclerotium cepivorum, leading to “white rot” disease

  • (exogenously-imposed dormancy)

T/F: Fungal spore diversity over the Earth is massive regardless of the geographical location

TRUE

Fungal spores are dominant over _

water, landmasses, and even air

Most fungal spores produce _ that are dispersed by wind over small or large areas

airborne spores

Fungal spore diversity is often due to components for air dispersal, including those for _

• Takeoff: how to get airborne and break boundary layer of air

• Flight: how to remain airborne; resistance to desiccation (hydrophobins), protection from UV (pigments)

• Landing: deposition for future development; siw sedimentation, impaction, washout

_ ensure that spores are dispersed at a distance from their origin structures

Ballistic propulsion methods

Marine fungi have _ to colonize surfaces

mucilaginous appendages

Explain structure of Pilobolus and its adaptations

• Structure

  • Sporangial stalk = moves to adjust to direction of light

  • Transparent vesicle = source of explosive force to eject sporangium, sensitive positioning mechanism that responds to light

  • Sporangium containing spores

• Adaptations pel

  • Phototropism = spore-bearing structures only shoot spores where light can pass (so spores can be shot away)

  • Explosive discharge mechanism = to shoot spores or spore-bearing structure away

  • Large projectile = based on ballistic principle, large/heavy objects will travel farther than smaller objects when launched at same initial velocity

Most groups of fungi inhabiting aquatic environment have _

appendaged spores

Fungi living in aquatic habitats have spores with _

unusual shapes and conspicuous appendages

Although structurally similar, spores of marine fungi may serve different functions, including _

isec

• Increase surface area for nutrient absorption

• Sedimentation and anchorage

• Entrapment of bubbles for flotation

• Catch raindrops for dispersal

T/F: Aquatic fungi have mucilaginous appendages to colonize surfaces

FALSE

Marine fungi have mucilaginous appendages to colonize surfaces

Some fungi use _ to get airborne, examples of which

• Water splashes

  • Splash of wet spores

  • Puff of dry spores

  • Tap effect of hail

Explain figure shown

• Splash discharge and its mechanism of attachment to vegetation of Bird’s Nest Fungus (Basidiomycota)

  • When water droplet hits petiole, spores are lodged out and in the vicinity, they can release flagella-like structure that allows them to latch onto plants

  • BUT they need water droplets first to get airborne

Enumerate examples of spore dispersal mechanisms

• Wind

• Ballistic propulsion

• Water (mucilaginous appendages)

• Water + Wind (splash discharge)

• Animals

• Zoospores

T/F: Spores produced associated with mucilage allow them to hitch a ride on insects

TRUE

Explain spore dispersal via animals

• Insects and small arthropods can disperse several types of fungi and their spores

• Mucilage production (in fungi) that enables sticking of fungal structures

• Fungi takes advantage of searching behavior of vector to reach a new site

• These interactions can be incidental or can become highly evolved mutualisms, as in the case of Dutch Elm Disease caused by Opisthioma ulmi and O. novo-ulmi (Ascomycota)

_ enables sticking of fungal structures

Mucilage production in fungi

Explain Dutch Elm Disease Cycle arising from fungal spores being dispersed via animals

1. Adult beetle relocates to a healthy elm tree, transferring disease to that new tree

2. Large elm bark beetle then feeds on English elm twig, depositing spores of Dutch Elm Disease

3. Disease spreads from the feeding wound throughout the tree

4. Neighboring elm trees become contaminated through natural root graft

5. Female beetle lays its eggs in the bark of dead and dying elm trees

6. Beetle eggs hatch and larvae feeds on trunk, creating tunnels with distinct patterns called galleries

7. Fungal pathogen then starts to produce spores in the tunnel galleries, causing emerging adult beetle to be covered in fungal spores, such that

8. Fungal spores will be dispersed by the beetle once it emerges from the bark and relocates into a new elm tree, repeating the cycle

Zoospores can use _ for dispersal

flagellar or amoeboid movement

_ are the only group of Fungi with zoospores

Chytridiomycota

_ refers to the release of vesicle contents for attachment to a surface or a host

Encystment

_ are motile, wall-less cells that swim via flagella using endogenous reserves

Zoospores

Zoospores have sensory perception, evidenced by _

presence of receptors on their cell surface, allowing them to locate sites of encystment (release of vesicle contents to attach to surface/host)

_ refers to the pattern of recognizing a substrate/host and triggering germination

Homing and docking sequence (of zoospores)

Explain homing and docking sequence in zoospores

• Zoospore chemotaxis (to locate sites of encystment)

• Oriented encystment

  • When zoospore positions itself properly on host/substrate, shedding its flagella, growing

• Cyst (spore without tail but with vesicles mobilized and stuck to substrate)

• Germination from a fixed site

• Infection via germ tube/hyphal structure/infection peg

_ movement is present in some Chytridiomycota; can alternate with swimming

Amoeboid (of zoospores)

T/F: Fungal spores will have differences from average somatic fungal cell

TRUE

Most unique dispersal strategy

Zoospores because the spores can swim (feature no longer existing in Modern Fungi)