3. Molecular Responses to Flooding Flashcards
Structure of the lecture
- The global flood stress
- What does flooding mean to a plant?
- Hypoxia: ERVIIs
- Mitochondrial stress: ANAC013
- Hormonal: Ethylene
What is the global flood stress?
1.1
Global flood stress is worsening with climate change. It involves crops undergoing detrimental effects due to submergence, and the negative impacts on growth and subsequent yield
What plants have beneficial flooding strategies?
1.2
Mangroves
Sub1 rice
We can learn from these plants and use genetic engineering to try to improve the global flood stress
How is flooding impacting the global economy?
1.3
Flooding severly impacts crop yield. The impact is currently increasing due to changing weather patterns, erratic rainfall, changing wind, rising sea levels and increasing global temperatures
What are the different types of flooding?
2.1
- Waterlogging
- Flooding. This can be either partial or incomplete
Why is flooding a stress to plants?
2.2
Submergence leads to carbon starvation (due to slow carbon diffusion and closed starvation), anaerobic fermentation, reduced photosynthesis (due to anoxia, turbidity, lack of light), and decreased soil redox.
This combines to lead to ROS, which is toxic, but also helps to build a response.
How do plants begin to perform anaerobically as a response to flooding?
2.3
- Anaerobic fermentation. The glycolytic cycle is maintained through the regeneration of NAD+
- Anaerobic nitrate cycle. Use of plant phytoglobins, nitrite in the ETC, and nitrate reductase to regenerate oxidised NAD+
What is an ERFVII?
3.1
ERFVIIs are Ethylene Response Factors. They are TFs that regulate early responses to hypoxia.
What is the mechanism of ERFVIIs?
3.2
- The N-degron pathway determines the instability of proteins dependent on their N-terminal amino acid
- All ERFVIIs have a conserved cysteine in position 2 of the N-terminal making it highly unstable
- ERFVIIs are constantly being degraded by the N-degron pathway.
- However, when hypoxia occurs, ERFVIIs will be stabilised by ethylene, stopping degradation from the N-degron pathway, which is inhibited
- ERFVIIs can finally flood the nucleus via translocation, and activate hypoxia-responsive genes
How is oxygen-signalling similar in animals and plants?
3.3
Both animals and plants rely on the aerobic degradation of constitutively expressed TFs to detect oxygen. When these molecules are no longer being degraded, they will accumulate, which indicates hypoxia, and allows for responses to occur.
This occurs via N-degron degradation of ERFVIIs in plants, leading to HRG activation
This occurs via O2 -dependent enzymatic degradation of the HIF1-α TF in animals, leading to inducible metabolic and developmental genes
What is the potential of ERFVIIs for plant breeding?
3.4
PRT6 mutations in the N-degron pathway enhances more ERFVII production, and can be used to upregulate crop production
Example: How many ERFVIIs in A. thaliana?
3.5
A. thaliana has 5 ERFVIIs TFs, of which two are involved in hypoxia-induction
How is ethylene involved in hypoxia response?
4.1
Ethylene is used to maintain homeostasis. Ethylene stabilised ERFVIIs, allowing them to move to the nucleus and activate HRGs
How can Ethylene be manipulate to increase flood-tolerance during flooding?
4.2
Ethylene acclimates plants to submergence. Ethylene pre-treatment improves plant-tolerance to hypoxia tolerance, as it will be transcribed more heavily during submergence. This is a form of stress priming
This has been tested by Hartman et al., 2019
How can HRGs be activated due to mitochondrial stress?
5.1
The transcriptional factor ANAC013 will be induced by hypoxia. ANAC013 is ER-localised but can be cleaved by rhomboid proteases during mitochondrial stress/dysregulation, leading to HRG activation
