3.VL Lipka Models 1

• fungal pathogen: magnaporthe grisea

  • hemibiotrohic

powdery mildew: conidiospore- germtube- appressorium- haustorium infects a single cell, via lytic enzymes and pressure

magnaporthe grisea (rice blast): conidum- germing- penetration of cell wall via melanised appresorium

Uromyces (rust fungus): enters trough stomta (thigmotrophic) degredation of cell wall, with lytic enzymes and builds a network trough the cells, invasion of leaves mesophyl

Melanin strengthens the cell wall (electron dense molecule), it is important for the apressorium to be able to built up the turgor (inner cell pressure) needed for host cell invasion.

Melanin provides a barrier to Glycerol influx/efflux, but is freely permeable to water which rapidly enters the cell, generating hydrostatic pressure

Magnaporte invades its host cell with cell wall degrading enzymes and pressure. External matrix around appressoria contains cutinase, cellulases, and other enzymes to help soften the cuticle, thereby aiding adhesion and penetration.

The apressorium with melanin in the cell wall builds pressure by generating Glycerol through glycolysis, which is highering the turgor (with pulling water into the apressorium from surroundings), then shooting a penetration peg through the softened host plant cell wall.

• biotrophic basidiomycete: Uromyces appendiculatus

• invades leaves example: barley, beans

• it build small “rust fleck” composes hundreds of urediospores and develops from mass fungal beneath the plant epidermis

• enters host through the stomatal aperture (Öffnung) from an appressorium

• The fungus senses a particular level of elevation (0.5 micrometers)

• signaling cascade allows reorganization and formation of appressoria

• after stomata recognition: invasion of leaf mesophyll (place of photosynthesis) using cell wall-degrading enzymes (chitin deacetylase, proteases, acidic cellulases, etc.)

It degrades the cell wall of the host cells with variety of enzymes:

Proteases, acidic/neutral cellulases, pectin methylesterases, polygalacturonate lyases dissolve the cell wall.

Aminoacid permeases provides nutrition to fungus.

Chitin deacetylase transforms chitin into cellulose, which causes the fungus to not be recognised by the host cell

• the sensing of signaling pathways can be a potential mechanosensing of the fungi

• receptor proteins are sensing the reorganisatio of the of the cell wall

Rust fungi can produce asexually and sexually, form basidiospores and aeciospores (monoploid and diploid possible).

Thereby they can switch their host organism, for example from barberry (dicot) to wheat (monocot)

Colletotrichum species that are causing anthracnose on host planst

anthracnose : fungal diseases that cause dark sunken lesions

Colletotrichum invades the host cells through germination of the spore, development of an apressorium and pressure penetration of the plant cell wall. Then, in the biotrophic phase it develops thick primary hyphae in the first feeding cell, that don’t produce toxins. To invade neighbouring cells, it produces thin hyphae that also produce toxins, switching to the necrotrophic phase. In this phase it also produces spores.

All of this is controlled by coordinated temporal gene expression.

• necrotrophic

• Botrytis spec.

• uses phytotoxic Botrydial

  
  

They both produce sphinganine-analog mycotoxins (SAMs)

Fumonisin B1 (FB1) and AAL toxin cause cell death in plants and animals by inhibiting sphinganine-N-acetyltransferase (ceramide synthase) which leads to an accumulation of sphingolipids and sphinganine bases that are known as secondary messengers involved in programmed cell death

- ubiquitous soil inhabitants

- exist as saprophytes, plant endophytes, but also as plant pathogens

- colonizes the vascular tissues

- first fungal species to serve as a dual model for fungal pathogenicity in plants and mammals (immunodepressed mice)

- Shown to harbor lineage specific (LS) chromosomes (hypothesis: horizontal chromosome transfer; Nature 464, 367-373))

Fusarium oxysporum, also referred to as Panama disease or Agent Green

- a biological weapon

The mutual benefit

• Carbohydrates for the fungus

• P, H2O, Zn, Cu, N for plant

• fungal hyphae are a lot smaller than plant root hair —> increase surface area for nutrient uptake

Ectomycorrhiza: outside of plant roots, classical forest mushrooms. Basidiomycetes mostly (also some ascomycetes) form large fruiting bodies, fungi interact with a variety of plants.

Endomycorrhiza: fungus grows on outside and in between (not inside!) root cells

• phosphorus is taken up from soil as inorganic phosphate (HPO3-)

• HPO3- has a low solubility —> phosphate near root is rapidly depleted(verbraucht)

• mycorrhizal fungi extend farther into soil —> enhance phosphate assimilation