SIGNALLING PATHWAYS OF ABIOTIC STRESS RESPONSES (1) Flashcards
Describing the major messengers involved in signalling pathways underlying the acclimation to abiotic stresses. Explain the mechanisms underlying signal transduction in plants. Discuss the methods used to unravel stress signalling pathways.
WHAT IS SIGNALLING?
Environment —»> Signal —»> Receptor —»> Signal cascade (black box of molecular events) —»> Phenotype stress acclimation:
- change in stomatal aperture
- modulation of developmental program
- accumulation of compatibles solutes and protection compounds
Why study abiotic stress signalling?
Crop yields are strongly constrained by adverse climate 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.
In the future:
> increasing population in the South
> climate change
Why use Arabidopsis thaliana to understand plant genes?
Avery 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
ABA accumulation in Arabidopsis plants subjected to a dehydration and dehydration + rehydration.
Does this prove that ABA is necessary for water stress response?
Resistance to soil water deficit of plants genetically modified to synthesise more or less ABA than wild type plants.
Is ABA necessary for stomatal closure under drought conditions?
ABA accumulation under well-watered and dehydration conditions of a mutant impaired for ABA synthesis. —»> dehydrated had more ABA accumulated
ABA SIGNALLING CASCADE
…NEED TO UNDERSTAND…
…YOUTUBE VIDS…
CALCIUM SIGNALLING
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.
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 produces ROS.
The ROS systemic signal replies on RBODH in Arabidopsis.
ROS make good long distance stress messengers:
> Naturally produced during stress
> Hydrogen peroxide can across 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
APX = ascorbate peroxidase
MDAR = monodehydroascorbate (MDA) reductase
DHAR = dehydroascorbate (DHA) reductase
GR= glutathione reductase
AsA = ascorbic acid
GSH = glutathione
GSSG= oxidised glutathione
> Required reducing power provided by NAD(P)H
> High affinity for hydrogen peroxide: efficient under low [H2O2]
