L11 - Introduction to beneficial plant-microbe interactions Flashcards
Where do plants encounter beneficial microbial organisms?
Phyllosphere
- Surface of stems and leaves
Rhizosphere
- Zone influenced by root secretion
- few mm in nutrient rich soils, several cm in nutrient poor soils
Briefly outline the structure of the rhizosphere and where microbes are found within the rhizosphere
- Comprises endosphere and and ectosphere
- Microbes found in both, up to Casparian strip
Are these microbial interactions always beneficial?
- Many “neutral”, some beneficial, some pathogenic
- Plant must evolve recognition mechanisms to differentiate foe and friend
What effect can a plant’s microbiome have on its phenotype?
How are plants and their microbial communities assembled?
- Plant growth promoting microbiomes improve plant health + growth
- Via assisting nutrient acquisition, pathogen defence, adaptation to environmental change
- Not randomly assembled
- Follow reproducible principles
- Often a consistent “core community” found but additions depend on environment
Define symbiosis and outline the three different forms of it
Symbiosis - Intimate living relationships between different species
1) Parasitism - one partner benefits to detriment of other
2) Commensalism - one partner benefits, no harm to other
3) Mutualism - both partners benefit
- Continuous spectrum
Give the three ways in which mutualistic symbioses are achieved
1) Exchange of services (rare)
2) Exchange of resource for service (common)
3) Exchange of resources (most common)
Give an example of a mutualistic symbiosis based on the exchange of services
Ants and Bullhorn acacia:
- Acacia provides home for ants in stipular spines
- Acacia species deficient in bitter alkaloid production
- Ant produces irritant pheromone that deters livestock
Give an example of a mutualistic symbiosis based on the exchange of resource for service
Insect pollination:
- Insect pollinates flowers in exchange for nectar
Give an example of a mutualistic symbiosis based on the exchange of resource for resource
Trade of photosynthates for mineral nutrients in plant-microbial interactions
- mycorrhizal fungi endosymbiosis
- nodulation root endosymbiosis
Describe an example with shows that parasitism-mutualism is a continuum in which one organism can be both mutualistic and parasitic under different conditions
Epichloë-grass associations:
- Epichloë geneus fungal endophytes infect cool season grasses
- Plant provides shelter, nutrients and dissemination mechanisms
- Fungus improves drought tolerance and production of alkaloids e.g. ergot to inhibit herbivory
MUTUALISM:
- fungus beneficial when in asexual form
- transmitted via plant seed to next generation
- grows strictly intercellularly in grass leaves
- coordinates growth w/ plant’s growth
PARASITIC:
- fungus switches to sexual form, can be triggered by grass flowering
- suppresses host’s inflorescence (choke disease)
What genetic causes have been seen to underlie the switch form mutualism to parasitism in Epichloë?
- Ryegrass infected w/ Epichloë mutated in MAP kinase SakA have stunted growth + early senesce
- MAP kinase SakA involved in ROS production
- Disruption of MAPK SakA = uncontrolled + irregular fungal growth pattern
- Affects plant development = parasitic
Sketch the relevant diagram that illustrates the continuum between mutualism and parasitism and when the interaction switches from one form to another
See relevant diagram on pg 5
