Signal Transduction Flashcards
How can trees respond to mechanical stress over time?
A build up of galactan sugar (hemicellulose) instead of lignocellulose
Give two examples of plants that can ‘move’
Venus flytrap and Mimosa Pudica
Definition of thigmonasty
Response to touch
What do long term and medium term responses require that short term does not?
Changes to transcription and translation
At what concentration can you see an effect to a plant from a hormone?
Extremely low concentrations
Why is it beneficial that hormones would have a highly complex shape?
To avoid other chemicals naturally occurring being able to mimic the pathway found in plant transduction.
Explain the process of a ligand molecule being accepted by a receptor
A hydrophobic ligand molecule passes through the membrane to reach a receptor within a cell. If it is hydrophilic it is accepted by a receptor on the cell surface.
Three types of membrane receptors in animals?
1) G protein coupled receptor
2) Enzyme coupled reactor (kinase)
3) Ion channel coupled reactor
Are all plant receptors found on cell surface?
No, brassinosteriods is but many others are found on the endoplasmic reticulum or chloroplast meaning those hormones must be transported into the cell or somehow activated within the cell.
How many genes does the arapidopsis genome encode for?
30,000 same as humans
What are the key differences between animal transduction pathways and what is found in the Arabidopsis genome?
Arabidopsis has only 1-2 G protein complexes (800 in humans) 1000 genes (4%) encode protein kinases 600 genes (2-3%) encode for ion channels
What is the role of a kinase enzyme
Takes last gamma molecule of ATP and attach to target.
What do kinase enzymes work in tandem with?
Protein phosphatases
Describe the structure of a plant protein kinase
Large extracellular (leucine rich) subunit Membrane spanning domain And an intracellular kinase domain
What is the MAPK pathway?
Mitogen activated protein kinase cascade
Series of phosphorylation reactions from MAP4K to MAPK in order to get a signal from the membrane of a cell across the cytosol (since the cascade massively amplifys the signal) to the nucleus. Once signal reaches target protein, a kinase phosphotase can dephosphorylate (inactivate) the MAPK protein kinase. Usually passes growth signals in animals, purpose more varied in plants.
How does the phosphorylation of the target protein affect transcription?
Transcription factors
How does MAPK system regulate specificity?
Each step in MAPK sequence can be present or not present in each type of cell. Since each signal is specific to the next MAPK, the pathway will not function without all of them.
What is a secondary messenger?
Can be small molecules or ions (oxidative species, calcium) that affect other molecules.
Describe a calcium pathway in plants that involves MAPK also
Hormone hits cell surface, phosphorylating MAPK which then results in the opening of calcium channels. This influx can then bind to target protein of Calmodulin which then acts as a transcription factor. The signal must then be degraded to get rid of calcium using ATP to get it outtta there.
How are superoxides produced?
Electron lost in the transport chain, normally in high stress environments.
Why are transcription factors particularly valuable for biotechnology?
They can result in many downstream outputs.
Describe the role of ZAT6
Regulates root development (repressor for primary root development) and phosphate adquisition and homeostasis
What is WRKY and why is it called that?
Transcription factor - due to double repetition in amino acid sequence (tryp, arg, lysine, tyrosine)
Describe full structure of WRKY
Rich serine proline repeat section at the beginning followed by double repeat of WRKY motif.
What induces OsWRKY30 and how long does it take?
drought or ABA which is normally produced by plant in general stress conditions. 3-6 hours
Role of Green Flourescence protein in biology?
Can make it be expressed in conjuction with gene of interest along with a 35s promotor (constitutively expressed) to track gene expression down to subcellular level.
Why is overexpression useful?
Can be caused by a 35S promoter to give insight into thw role of genes. Eg. in rice overexpression of WRKY results in drought tolerance.
WHat is the role of polyethylene glycol (PEG)
Mimicks drought coniditons by giving lower osmotic value.
Why do MAPKs move towards WRKY transcription factors?
They are attracted to proline rich area
What is the biochemical sequence around WRKY?
MAPK phosphorylates proline area of OsWRKY which can then go on to bind to the transcript in the nucleaus of the required gene.
How can you track this phosphorylation chain?
Use radioactively labelled ATP.
How could you produce WRKY and MAPK proteins seperately?
Insert gene for each in chromosome of two e coli strains and allow each culture to grow before isolating proteins with either a resin or antibodies.
What would an SDS page show of these two proteins apart and then together?
Shows phosphorylation occuring between MAPK3 and OsWRKY.
What was found when all ser was subbed out for alanine?
No drought recovery was possible hence the proline is essential for attracting MAPK.
Is this WRKY promotor being commercialised?
NOPE
Which two aspects of plant cell walls are being modified?
cellulose synthase on cell curface
matrix polysaccharides in golgi apparatus
Difference between primary and secondary cell wall?
Primary soft no lignin random cellulose fibrils- secondary appears after primary (all have primary) with thick lignin. cellulose laid down in thick ribbons
What happens when hormone brassinosteroid is added to arabidopsis cell culture?
Xylem vessels (for transpiration in secondary requires lignified xylem) appear with secondary cell walls.
What genes change with addition of brassinosteroid? (hence linked to secondary cell wall production)
NST (thickening)/VND transcription factors results in aligning of tubulin and microtubules and resulting in secondary cell walls?
Why are cell walls important?
They are the main content of biomass as cell wall is straight sugar hence energy supply.
Main elements of a cell wall?
Hemi cellulose - 5C sugar
Cellulose 6C sugar
Lignin - not sugar
Two stages required to use cell wall as energy supply
Pretreatment - seperate different elements apart
Enzymatic breakdown release sugars
Microbes turn to biofuels
Problems with biofuel?
Its not dense - full of holes so not good volume to energy ratio
need biorefinery in middle of 10 m paddock to make it economically viable
What happens if you overexpress NST/VND master regulator to make secondary cell walls?
end up with secondary cell walls all over the shop and affected photosynthesis of plants in leaves. Needs to be more targetted.
How do you make secondary cell wall production specific to locations around plant?
Add tf for IRX promotor (9) thats only appears on secondary cell walls to your NST gene. This means plant will keep making this tf with NST resulting in densely packed cells (10/20% increase) in stems.
