Signalling 1 rewatch Flashcards
What is signalling?
give some examples of what might be changed?
environment, starts a signal off in the plant which gets sent to a receptor which will then begin a cascade leading to a Stress acclimation:
- change in stomatal aperture
- modulation of developmental program
- accumulation of compatibles solutes and protective compounds
Why study abiotic stress signalling?
Crop yield is strongly constrained by adverse climatic conditions:
→ need genetic improvement (breeding/genetic modifications) for abiotic stress resistance
Genes involved in stress signalling can impact the expression of many stress response genes.
Why use Arabidopsis thaliana to understand plant genes?
A very good model species to uncover the function of genes:
Small, easy to grow under controlled conditions
Short life cycle (3-5 months), produces thousands of seeds
Small genome sequenced in 2000
Several libraries of mutants available
Genetic modifications easily done
Abscisic acid: a plant stress hormone
plants need to pass information on from one part of the plant to the other and they do this by hormones.
Passes on stress information
ABA accumulation in Arabidopsis plants subjected to a dehydration and dehydration + rehydration
Resistance to soil water deficit of plants genetically modified to synthesize more or less ABA than wild type plants.
as plant ABA accumulated in the plant when they were getting dehydrated however when they were given water ABA in the plant decreased.
(this is correlation not causation so no actual evidence that they are linked so more experiments needed such as ABA deficient plants)
plants that don’t have as much ABA are less likely to survive stress
Is ABA necessary for stomatal closure?
Inject ABA in solution to a leaf. This shows that ABA does close stomata. They measure aperture gets smaller and after about 30 min are fully closed.
This isn’t done in realistic conditions depends on question.
also plant wasn’t stressed it was artificially injected.
Is ABA necessary for stomatal closure under drought conditions?
ABA accumulation under well-watered and dehydration conditions of a mutant impaired for ABA synthesis
plants that have open stomata are colder that when they are closed
Leaf temperature of a mutant impaired for ABA synthesis blue=cold red=hotter (on slide) therefore we can assume which ones are open
ABA signalling cascade
receptor of ABA is very important inetraction between different proetin sthat transmit signals.
When lost of ABA during water stress, they get detected by recepetrs, recepter get activated which interacts with protein phophotase which blisks protein kinase. When ABA is present
protein kinase SnRK2 is only activated after phosphorylation???
Reminder on gene expression regulation
ABA signalling cascade
enzymes that do phosphorylation are kinases. The ones that dephosphorylate are called phosphatases. When shape is changed, function is changed (active/non-active).
transcription factor links to promotor and induces??
Another version of cascade that in stomata activates an anion channel an important part of stomatal closure.
Identifying genes in a signalling cascade
Screen mutants for changes in leaf temperature under drought conditions this shows whether stomata is open or closed
on example is a kinase gene being mutated that gives different mutants.
mutants OST1 have mutated gene SnRK2-6
Decreased ABA sensitivity of stomata in ost1 mutants
OST1 = SnRK2-6
Calcium signalling
macronutrient so high amounts in plant however it can be toxic.
Ca2+ can bind to negatively charged groups on biological molecules. This makes it toxic in high concentration in the cytoplasm so it is usually compartmented in organelles.
Variations in Ca2+ concentration in the cytosol and other compartments is used as transient cellular signal in plants (and other organisms).
Ca2+ concentration in the cytosol can increase quickly and sharply through release from the vacuole and influx from the apoplast, relying on the action of a high number of channels and pumps.
Calcium signatures
The shape of variations in [Ca2+]cyt (and in other compartments) transmits information about specific environmental stimuli.
Amplitude and frequency of oscillations can be related to the intensity, as well as the nature, of the stimulus. Different calcium signatures will trigger different responses. (when looking at graphs be aware of time is min or sec
The signal conveyed by [Ca2+] needs to be decoded. There is a large number of calcium sensors:
sensor relays when bond by calcium can regulate the activity of other proteins (e.g. calmodulins (CaM), calmodulin-like and calcineurin-like proteins)
sensor responders when bond by calcium can carry out an enzymatic activity (e.g. Ca2+ dependent protein kinases (CDPKs) and Ca2+/CaM-dependent protein kinases)
Ca2+ oscillations are dependent on feedback loops.
ROS: deleterious compounds repurposed as signal molecules
RBOH are NADP oxidases that produce ROS.
RBOH genes are necessary for abiotic stress acclimation.
The ROS systemic signal relies on RBODH in Arabidopsis.
ROS make good long distance stress messengers:
Naturally produced during stress
Hydrogen peroxide can cross membranes
The ROS signal can be propagated rapidly
Many ways to scavenge (AG cycle) and produce (Rboh)
The way information is encoded in the ROS signal is still unclear (similarities to calcium?), but ROS signal has been linked to other elements of signalling pathways (hormones, calcium and phosphorylation).
ROS scavenging
Ascorbate glutathione cycle:
Converts hydrogen peroxide into water
Requires reducing power provided by NAD(P)H
High affinity for hydrogen peroxide: efficient under low [H2O2]
