plant-microbe interactions Flashcards
- rhizosphere
- phyllosphere
- below ground/environment around roots
- above ground/leaf environments
- biotrophic pathogens
- necrotrophic pathogens
- require living cells for infection.
- parasitise dead plants.
virulence factors (effector proteins)
possessed by microbial pathogens and helps it to colonise plants.
resistance genes (R genes)
possessed by plants. scan cytoplasm for virulence factors.
recognition of virulence factors triggers plant defence responses to prevent host colonisation.
avirulence proteins
effector proteins or virulence factors which have been recognised by R genes.
race specific resistance
R proteins and effector proteins must correspond for resistance to occur. requires pathogens to be of the right race.
hypersensitive response
following recognition of pathogen cell death is initiated in an attempt to remove nutrients from the pathogen.
why does a leaf having lesions mean it is healthy?
the lesions are a response to pathogen infection. they are cell death preventing spread of the pathogen to other cells and the rest of the plant.
a leaf with no lesions means it is not resistant and cannot trigger cell death as a response.
durable, broad spectrum resistance
following successful immune response the plant has the ability to protect itself against future pathogens.
SAR
Systemic Acquired Resistance - plant infected with avirulent pathogen. this causes no harm but induces resistance in the plant to virulent pathogens.
PR proteins
pathogen related proteins.
proteins synthesised following infection from pathogen. they accumulate in local and systemic leaves.
what was salicylic found to be capable of?
induce SAR.
bion
safe, SAR inducing agrochemical for agriculture.
rhizobia
soil bacteria - helps plants with nitrogen fixation through symbiosis. they have the ability to reduce nitrogen to ammonia for use.
they are gram negative
three rhizobia genera
- rhizobium
- bradyrhyzobium
- azorhizobium
how does signalling induce nodule formation in legumes?
- legume roots release flavonoids.
- flavonoids induce chemotaxis of rhizobia and they move towards the legume roots.
- flavonoids induce the expression of nod genes in rhizobia.
- nod factors induce nodule formation.
flavonoid functions
- chemotaxis
- nod gene activation
- increase growth rate
nod D
- expressed all the time.
- promotes expression of other nod genes
physical process in root nodule formation.
- bacteria attach to root hair.
- this triggers curling of the hair, enclosing the bacterium.
- infection thread is formed from bacteria and grows int plant root.
- infection thread triggers multiplication of cortex cells in root.
- infection thread divides and expands and forms nodules where nitrogen gets converted into an available nitrogen source.
SYM pathway
signals from modulating bacteria are transducer from the plasma membrane to the nucleus.
how does bacteria get from infection thread to formation of a nodule.
bacteria exits infection thread into cortex cells as membrane bound symbiosomes.
determinate nodules
homogenous and lose apical meristem.
indeterminate nodules
retain nodule meristem that is the site of cell proliferation and have zones of different activities.
nitrogenase
enzyme used in the production of ammonia.
activity is suppressed by oxygen.
