Mycology L2: Fungal Cell Biology and Development

*Spitzenköper

- A dense aggregation of vesicles in growing hyphal tips -this component of the endomem sys. is unique to higher fungi (asco and basidia) -create new membrane surface through exocytosis and deliver new cell wall materials

Rice Blast

- fungal disease affecting rice. -found in 85 countries -responsible for ~30% of rice production losses= feeding 60 million people

What are the main structural components of fungal cell walls?

-Chitin microfibrils -Linear polymers of glucose (glucans) -variety of cell wall proteins (CWP; glycoproteins)

Notable differences between fungal and plant cells:

-Fungal cells lack chloroplast (fungi are heterotrophic not autotrophic) -Cell walls in fungi are made of chitin rather than cellulose

What advantages are seen when considering that fungi have chitinous cell walls?

-It is easier to digest cellulose and lignin if you aren't made of it -suggest 'recent' evolutionary link to animals

cell wall proteins

-Their sugar residues form covalent links with other cell wall polymers and help to maintain cell shape -signaling and transport functions -cell fusion -adhesion to surfaces -biofilm formation -pahtogenesis -mediate absorption of compounds

What do skeletal and binding hyphae have in common?

-They are usually empty of cell contents -just empty cell wall structures for support

septal pore cap

-a curved double membrane arching over a septal pore -formed from the endoplasmic reticulum -same role as Woronin bodies in ascomycota

Rhizomorph anatomy

-a gas filled lumen occupies the center (allows for oxygenation of tissue -surrounded by living cells produced on the exterior of the rhizomorph -young hyphae are pushed inward as they age;eventually replaced

Cell wall components: cholesterol

-aids in stabilization -provides dense organization of phospholipid bilayer -fungal cells do not have cholesterol (but has similar molecules)

What occurs following host penetration?

-biotrophic pathogens produce haustoria that absorb nutrients from the plants, and secrete virulence proteins call effectors that manipulate the host, without destroying the infected cell

**Why might turgor be important for fungal cells?

-helps fungal cells push through substrate -helps fruiting bodies free-stand

Largest organisms on earth?

-humongous fungus -Armilaria ostoyae

Boletinellus Merulioides Sclerotia

-makes sclerotia -some are solid and serve typical purpose -others are hollow and serve as homes for aphids that feed on ash--> aphids produce waste--> feeds mushrom

Historically: Sclerotia

-many thousands died in middle ages due to ergotism -causes paranoia/hallucinations, spasms, edema, vasoconstriction -misinterpretation of the symptoms may have lead to accusations of witchcraft during the salem witch trials

monolithic hyphal system

-only has generative hyphae -anything that has clamp connections

Woronin bodies

-organelles found near septet that protect the mycelium from catastrophic injury by plugging septal pores on either side of a wound

What is the role of Hyphae?

-ramifies within substrate -digest and absorbs nutrients -maximize SA for absorptive nutrition

Ergosterol

-the major cell membrane sterol found in fungi -performs a similar function to cholesterol

Why does the cytoplasm of growing yeast and mycelium contain a higher concentration of salts and sugars than the surrounding fluid?

-this allows for an osmotic differential to drive the net influx of water through the plasma membrane and cause cell expansion -maintain turgor

Amphotericin B and Terbinafine hydrochloride

-used to target ergosterol synthesis -lyses fungal cells

generative hyphae

-usually still alive and bear spores

Rhizomorph importance

-wood rotting fungi -resources may be separated by relatively great distances and spatial nutrient scavenging is important

dolipore septum

A septum which flares out in the middle portion of a hypha, forming a barrel-shaped structure with open ends. Characteristic of some Basidiomycetes.

Example of a genus that uses rhizomorphs:

Armilaria spp.

What is an example of a trimitic fungi?

Artists conk ganoderma applanatnum

why do basidiomycetes produce a clamp connection?

Because nuclei cannot migrate due to the dolipore septa

Why do biomolecules not passively diffuse through the membrane?

Because they are found in much higher concentrations inside the cytoplasm

Why are ion transport functions catalyzed by transmembrane proteins critical for understanding fungal physiology and energy acquisition?

Because they are heterotrophs that feed via EXTERNAL digestion (mostly)

Vacuoles are capable of:

Extension, retraction, and peristaltic shape changes

ToF: There is a significant division of tissue in fungi

False -Not much tissue differentiation in fungi, just different configurations of hyphae

ToF: Nuclei can migrate freely in basidiomycetes

False -due to the dolipore septa -This is why these fungi produce clamp connections as cells divide following fusion of compatible mycelia

ToF: nuclei form the largest endomembrane compartments

False Vacuoles do

ToF: the electrochemical gradient established by the proton ATPase activity is unrelated to absorptive feeding

False the electrochemical gradient is vital due to its power to aid in the import small molecules like sugars and amino acids

secondary active transport

Form of active transport which does not use ATP as an energy source; rather, transport is coupled to ion diffusion down a concentration gradient established by primary active transport.

Osmolytes

Organic compounds that affect osmosis

What makes polypores so tough?

Skeletal and binding hyphae

Binding hyphae

Sometimes thick-walled, tremendously and frequently branched

ToF: in filamentous ascomycete, the septa are perforated by a single pore, allowing the movement of material and organelles such as ribosomes, mitochondria, and nuclei

TRUE

ToF: mushroom caps and stems are built from thin-walled hyphae that differs only in diameter, spacing of septa, and frequency of branching

TRUE

ToF: primordial of basidiomata have differentiated tissue regions at very small stages

TRue

Why are septa important?

This process allows differentiation of mycelium into compartments that assume specialized functions in survival and reproduction

ToF: hyphal branches fuse with one another to form highly interconnected networks or webs

True

ToF: the cell wall is constantly being built in front of the expanding hyphal tip

True

ToF: beyond the primordial stage, the majority of growth is the result of elongation and expansion of pre-differentiated cells of primordium

True! -expansion is due to rapid water uptake

Dry rot

When timber (treated wood) is subject to decay and attack by fungus.

dimitic

a mushroom that posses generative and one other type of hyphae

Chitin

a polysaccharide composed of N-acetylglucosamine (a derivative of glucose)

Why are Amphotericin B and Terbinafine hydrochloride harmful to fungal cells but not our own?

because we don't posses ergosterol in our cell membranes so our cells aren't lysed

Clavicep purpurea

causes ergot on rye

Anastomoses

connection between hyphae -provide pathways for bulk flow of cytoplasm and regulated movement of organelles -can be seen in the hymenophore of some chanterelles

Ergot

elongated sclerotia -produced by claviceps

effector proteins

emitted by haustoria when inside a host to avoid pathogenic detection

primordia

fruit bodies beginning as small knots of branched hyphae

Rhizomorphs

fungal mycelia that have the shape of roots; transport water to other parts of the same mycelium

What are the three main types of hyphae?

generative skeletal binding

Sclerotia

hardened masses of hyphae containing food reserves (lipid and glycogen) that serve as survival structures for ascomycete and basidiomycetes -associated with over-wintering

endomembrane system organelles function:

in the secretory (export) and endocytotic (import) pathways that sustain fungal growth and development -within their endomembrane systems they have a collection of organelles that are not found in other organisms in the hyphal tips

Appressoria

inflated cells produced by plant pathogens on the leaf surfaces of their hosts -use high pressure to penetrate cell wall

skeletal hyphae

long, unbranched, thick walled hyphae

parenthosome

membrane between pore found in a dolipore septa -much finer filter when compared with ascomycete cells

pseudoparenchyma

oval or isodiametric fungal cells organized into tissues whereby individual hyphae cannot be distinguished

Vacuole function:

passive transport, storage of waste products/toxic substances -turgor

Startch and cellulose

polysaccharides composed of glucose monomers -Starch (1-4 linkage of alpha) -Cellulose (1-4 linkage of beta)

trimitic

posses generative, skeletal, and binding hyphae

isodiametric

round (cells)

Haustoria

specialized hyphae that allows an organisms to penetrate the interior of host cells

septa/septum

the cells that make up hyphae are divided by these cross sections

endomembrane system

the network of membranes connected either directly or indirectly -nuclear envelope, endoplasmic reticulum, golgi apparatus

Sclerenchyma (plants)

type of ground-tissue cell with an extremely thick, rigid cell wall that makes ground tissue tough and strong -similar to skeletal and binding hyphae