plant microbe associations Flashcards
Plant microbe associations
Positives:
Essential for C and N recycling
Important for plant growth (water and minerals)
Important to strengthen plant health
Negatives:
Detrimental to plant health
Threat to crop production for human food energy and energy
Threat to natural ecosystems
what associations do plants form with roots
mutualistic, symbiotic
what facilitates nutrient and water uptake
extensive fungal surface area
symbiosis
mycorrhizal fungi
what are mycorrhizal fungi
ecto or endomycorrhizal
where do ectomycorrhizal fungi proliferate
outside the root and between cells
where do endomycorrhizal fungi proliferate
within the cells
what do EM fungi form surrounding the root
networks
what does EMF form around the root tips
a mesh and also penetrate between the cells
what is the name of the enzyme that bacteria use to fix nitrogen
nitrogenase
Two-way signaling occurs between rhizobia and plant
- The plant root produces a flavonoid chemical that attracts rhizobia
- The bacterium produces a Nod factor, identifying it as a symbiont
- The plant prepares to form a symbiotic nodule structure
Symbionts
- Fungi and bacteria
- Fungal associations very old – helped colonise land
- Help to provide water and minerals
- Help to fix nitrogen (natural fertilizer for legumes)
- Receive carbon compounds (e.g. sugars) fromphotosynthesis
Saprophytes
Feed off dead/organic matter (plant and animal)* Fungi and bacteria
* Digest then absorb
* Extracellular (secreted) enzymes
* Carbohydratases, lipases, proteases
* Essential for N and C recycling
what must a successful pathogen do
*Find the host and attach to it
*Gain entry through the plant’s impermeable defenses
*Avoid the plant’s defense responses
*Grow and reproduce
*Spread to other plants
Plants are exposed to countless microbes, but very, very few of these interactions lead to disease. Why?
The pathogen must be able to overcome plant defense
The host plant must be susceptible to the pathogen
The environment must tip the balance in favor of the pathogen
Facultative
pathogens can attack living plant cells but can also grow by themselves, e.g. on artificial medium
Obligate
can only grow on their specific living host
Biotrophic
feed on living plant tissue, not causing cell deathexample=Hyaloperonospora arabidopsidis (oomycete)
Necrotrophic
kill plant cells and then feedexample=Botrytis cinerea (fungus)
Hemibiotrophic
initially biotrophic and then become necrotrophicexample=Pseudomonas syringe (bacteria)
Biotrophs
*“Pretend harmony”
*Fewer cell wall-degrading enzymes than non-biotrophs
*Evade detection and avoid limitation of defense responses
Necrotrophs
*“Smash and grab”
*Produce toxins and cell wall-degrading enzymes
what do Root-knot nematodes do
induce expansion in five to seven neighboring cells to produce giant cells
what do cyst nematodes do
partially dissolve cell walls between cells to produce syncytium
what do nematode effectors do in general
modify root cells to become specialised feeding cells
what is Hyaloperonospora arabidopsidis
it’s a biotrophic biotrophic oomycete that infects Arabidopsis
what does fungal and oomycete (hemi)biotrophs usually make
haustoria
what is haustoria
In botany and mycology, a haustorium is a rootlike structure that grows into or around another structure to absorb water or nutrients
where do Haustoria remain
outside the plant plasma membrane, and are specialized for nutrient and signal exchange
How do plant cells detect microbes?
receptor proteins on the surface of plant cells
How do they defend themselves?
recognize microbe-associated molecular patterns (MAMPs) of potential pathogens through pattern recognition receptors (PRRs) that mediate a basal defense response.
how do pathogens overcome the plant immune system
To cope with plant immunity, pathogens have evolved mechanisms to deliver effector proteins into plant cell, which target and inhibits immune signaling, as well as to subvert immunity through targeting of critical host cellular processes
How do plants then defend themselves from pathogens that can infect them?
Various natural compounds, ranging from cell wall components to metabolic enzymes
