A Little Help From Your Friends Flashcards
What kind of symbiotic relationships do exist?
Mutualistic
Parasitic
What do plants bring to the table in mutualistic relationships?
Food in form of carbohydrates
Shelter
What do plants generally gain in mutualistic symbiotic relationships?
Greater access to nutrients in the soil
Protection from parasites and predators
How did vascular plants evolve
From algae which formed a symbiotic relationship with aquatic fungi
Algae provided carbohydrates
Fungi provided inorganic nutriebts
How is the mutualistic relationship with fungi and plant roots called?
Mycorrhiza
What does the fungi provide the plant with mostly in mycorrhiza?
Phosphate
WHat are the two main mycorrhizal associations?
Ectomycorrhizae
Endomycorrhizae
How does a ectomycorrhizae work?
Also known as sheating mycorrhizae
The fungus surrounds the root, altough fungal hyphae also penetrate the root and grow between its outer cells (cortex)
How does a endomycorrhizae work?
Grow WITHIN the root and penetrate its cells - thsi forms an arbuscule
What is an arbuscule
A structure that a fungi forms in plants roots that resembles a cauliflower head - it provides a large surface area for uptake of sugars
It never ruptures the plants plasma membrane of the plant cells
Can mutualistic fungi just enter the plant?
They are recognized as alien organism by the plant
The plant recognizes two elicitor molecules during this encounter - those derived from the fungi itself and those created by the damage inside the plant
Ectomycorrhizal fungi lack enzymes that damge the plants cell walls - so they dont produce damage induced elicitors that trigger an immune response
The plant only triggers its defences as the fungus starts its interaction with the host - these defences then get suppressed by the fungus
What are effectors?
Molecules which block perception of elicitors
What is MiSSP7?
The most highly up regulated gene in the symbiosis of the fungus with plant roots
It encodes an effector protein which is indispensable for the establishment of a mutualistic symbiotic relationship between the fungus and the roots
How does MiSSP7 work?
1.The protein is secreted by the ectomycorrhizal fungus, once it detects signals of the plants roots
2.The protein is imported into plant cells via endocytosis (Molecules ate transported into the cell by engulfing them)
- Once in the cell it is transported into the nucleus where it alters the expression of genes involved in establishing the symbiosis
What makes it hard to work with arbuscular mycorrhizal fungi?
The fungi is biotrophic and cant grow away from its host
What is SP7?
An effector protein produced by arbuscular mycorrhizal fungi
It interacts with a transcription factor that is induced by the plant when it gets attacked -> thsi way no defences get activated
It is an universal effector
Which plant hormoned interact with the fungi in soil, stimulating its growth?
Strigolactones
How does the fungi signal a plant it is ionterested in symbiosis?
With molecules called „Myc factors“ which trigger a reprogramming of gene expression in plants
How can a plantregulate the symbiosis formed with organisms?
It is called autoregulation - when one half of the root already formed a symbiosis with a fungi, the other won‘t
It is suggested, that an inhibitor that gets produced upon mycorrhizal establishment is responsible for this
How do mycorrhizas contribute to plant health?
inproving plants nutritional status
How do plants attract mycorrhizal friends?
By exuding substances known as strigolactones
These compunds act as germination signals and induce branching in hyphae that promotes the colonization of the root
How does the production of strigolactones behave during symbiosis?
Before symbiosis they get produced a lot
Once the symbiosis has been established, their production and release is greatly reduced
What are roots good for?
They anchor plants in the soil, take up water and nutrients and store carbohydrates
What is a rhizosphere?
A region inhabited by microbes around the roots, usually shaped by the plant
How do plants establish their influence over the microbes in their rhizosphere?
They release a variety of biologically active compounds into the rhizosphere
These compunds can
-attract
-stimulate
-repel
-inhibit
-kill
The microbes
What do plant growth promoting rhizobacteria do?
- they suppress pathogens and „bad“ microbes in the soil
-they stimulate the plants ability to defend itself
Does the rhizobacterium itself induce resistance in plants?
No, they rather „prime“ the roots - eliciting systemic resistance
When they are removed from the root, the root can still protect itself
Which signalling molecules mediate the resistance via rhizobacterium?
Jasmonic acid and ethylene
Why cant you grow the same crop on a field for a long time without the soil getting bad?
There will be a lethal build up of the soils pathogen population
How can one tackle this pathogen build up?
There are five native bacteria that have to be applied together, not seperately
What are fungal endophytes?
Fungi that live INSIDE the plant
Every plant has these
How do fungal endophytes get transportet to the plants offspring?
They can grow inside their hosts seeds - this is called vertical transmission
What is vertical transmission?
The transmission of fungi by the mother to their offspring inside the seeds
What is horizontal transmission
Fungal propagules germinate on the surface of the foliage and enter the plant by penetrating the cuticle or by open stomata
How do endophytes provide protection against pathogens?
Production of toxic compounds
Inducing systemic resistance
What are lysergic acid and ergopeptides?
They are compunds that affect the central and peripheral nervous systems of vertebrates
They can act as agonists or antagonists of dopamine, serotonin and adrenergic receptors
What does lysergic acid do to vetebrates?
It has psychedelic effects in mammals
What do ergotamines do to vertebrates?
They cause the narrowing of blood vessels
How does the fungal edophyte of grasses provide protection to it?
With the production of toxic alkaloids
They also have a insect toxin gene
What is the mcf gene?
An insect toxin gene present in fungal endophytes that is originally transferred horizontal by a bacterium
It inhabits the gut of insect invading nematodes, that invade caterpillars - the bacteria is released into the insects bloodstream where it releases toxins that kill the caterpillar
What do endophytes provide leafs with?
A higher toughness - insects take 45% longer to chew them up
What causes the start of flowering in some fungi of flowering grass?
It starts the fungis sexual cycle in which it change from being asexual but mutualistic to being sexual and pathogenic
What came first: the endophyte or the pathogen?
It is suggested that it was the pathogen!
It is possible that the differentation among these different fungi occurred in response to the divergence of their respective host plants
What are plants called, that form obligate, symbiotiv mutualisms with ants?
Myrmecophytes
What do ants provide a tree with?
Seed predation and pathogens
Why do ants feed on the sucrose free nectar of acacia?
The ants cant digest any other nectars because the enzyme that would break down the sucrose (into frustose and glucose) is inhibited by chitinase
What is a nursery pollination system?
larvae of the pollinator develop in the plants flowers
What is special about Brassicas?
They dont have a mycorrhizal relationship but rather one with bacteria
