Surviving The Deluge: Flooding Stress Flashcards
1
Q
Plants and submergence
A
- Water excess, relatively common stress
- several wild species, but few crops thrive in such an environment
2
Q
Water logging
A
Only the below-ground part is under water saturating conditions
3
Q
Flooding
A
Partial and complete submergence
4
Q
Partial submergence
A
Root system and portion of shoot underwater
5
Q
Complete submergence
A
Whole plant covered
6
Q
Economic impact of crop flooding
A
Largest stressor!
7
Q
Dynamics of flooding events
A
- intensity, timing, duration = changing
- frequent: UK, CE, Balkan area
8
Q
Why is submergence a stress to plants?
A
- anoxia
- anaerobic activity of roots and rhizosphere
9
Q
ROS
A
- affect mitochondria and chloroplasts
- < photosynthesis
10
Q
Submergence process:
A
- Soil redox potential «
- Accumulation of toxic compounds (Mn2+, Fe2+, H2S)
- Gases diffuse 10^4 slower in water than air (severely «_space;O2, CO2 availability; ethylene entrapment)
- Fermentation
- Carbon starvation
- «_space;photosynthesis
11
Q
Anaerobic metabolism
A
- fermentations necessary to replenish glycolysis NAD+
12
Q
Fermentation process
A
- Starch -> soluble sugars
- Soluble sugars -(glycolysis)-> pyruvate (NAD+ -> NADH; ADP -> ATP)
- Pyruvate -lactate dehydrogenase-> lactate (toxic! Acidifies, damages cell) (NADH -> NAD+)
OR - Pyruvate -pyruvate decarboxylase-> acetylaldehyde (toxic!)
- Acetylaldehyde -alcohol dehydrogenase-> ethanol (preferred!) (NADH -> NAD+)
13
Q
Phytoglobins
A
- plant Hbs
- v high O2 affinity
- no long distance transport
- nitrate reductase: NAD+ regeneration
14
Q
Nitrite
A
Alternative e- acceptor in mETC
15
Q
A. thaliana ERFVIIs TFs
A
- 5x total
- 2x hypoxia-inducible (relative expression level across hypoxia time course)
- transient/permanent up regulation
- v conserved N terminus
- cysteine residue followed by 2x glycines
- very rare feature of proteins
16
Q
N-degron pathway
A
Determines protein (in)stability depending on exposed aas
17
Q
Oxygen-dependent oxidation of N-terminal cysteine (+R)
A
Prepares proteins for degradation
18
Q
Cysteine in 2nd position
A
- dangerous!
- exposure R residue; degradation signal
- PTM + R
- 4x possible pathways
19
Q
N-degron 4x pathway 1
A
- MC -MetAP-> C
- C -> *C
- *C -> RC
- RC -NO-> degradation
20
Q
N-degron pathway 2
A
- MC -> NQ
- NQ -NTAN/NTAQ-> DE
- DE -ART6/VBR1-> R
- R-Ub-> degradation
21
Q
N-degron pathway 3
A
- MC -endoproteolytic cleavage-> DE
22
Q
N-degron pathway 4
A
- MC -> R
23
Q
Hiding from N-degron?
A
Mask/decorate
24
Q
N-degron ERFVII regulation
A
- priming effect
25
N-degron mutant analysis
- mimic hypoxia
- ate1/ate2, prt6 -> mutant genes are core hypoxia responders
26
RAP2.12
wt = degraded
wt (hypoxia) = stabilised
ate1ate2 = stabilised
erfr11 = less DEGs under hypoxia (1% O2)
27
High O2
1. O2 + HIF-1α tags with Pro
2. PH tags with OH
3. pVHL targets for degradation
28
Low O2 sensing in mammals
No PH
29
PH
- prolyl hydroxylase
- transcriptionally regulated by HIF-1α
30
Summarising O2 sensing in mammals
- O2 dependent enzymatic proline residue hydroxylation in HIF-1α TF stimulates proteasomal degradation
- stabilised HIF-1α induces metabolic + developmental genes (e.g. angiogenesis)
31
For O2 sensing, both plants and animals rely on
aerobic degradation of a constitutively produced TF
32
Can N-cysteine oxidation be enzymatically catalysed in plants?
- localise in cytosol + nucleus (GFP localisation)
- 2x hypoxia inducible
- regulate other nuclear proteins?
33
Cysteine oxidase in planta
Oxygen sensors! PCOs
34
Oxygen sensing
Cysteine -O2 dependent cysteine oxidase- cysteine sulfunic acid
35
HUP29, 43
Cysteinyl dioxygenase activity; PCOs
36
PCO biochemical characterisation
Mass spectrometry analyses have confirmed that PCO can add 2x O2 atoms to ERFVII N-termini
37
ERFVII interacting proteins
- RAP2.12 interacts with ACBPs in PM
- shown by biomolecular fluorescence complementation assay; photoconvertible + UV
38
RAP2.12
Constitutive ERFVII
39
RAP2.12 behaviour under hypoxia
Nuclear localisation
40
HRPE
- ERFVII enhancer
- compare hypoxia promotors for signature
- trim + luciferase fusion construct: measure expression under hypoxia
- C9 motif KO: necessary
- 32nt 3x repeat KI: sufficient
41
ERFVII TF
Relocalisation and stabilisation in buckets to activate hypoxia genes
42
Can we target ERFVIIs in plant breeding? Logic
- modulating N-degron pathway (prt6) ; does this enhance plant flooding survival ??
- hypoxia tolerance assays in vitro
- submergence assays in soil
43
Can we target ERFVIIs in plant breeding? Results
- HRE1 hyper-expression = +ve
- hyperstability (masking N-terminal cysteine) severely compromises plant development
- silencing / spontaneous mutation = +ve
44
Hormone homeostasis under submergence
- phytohormone biosynthesis -> require O2 (+ATP) cosubstrate(s)
- hormone metabolism depends on enzyme oxygen affinity
45
Ethylene
- gaseous
- biosynthesis enzymes induced in hypoxia in several sp.
- ACS, ACO
46
Ethylene biosynthesis
Methionine -AdoMet synthetase-> S-Ado-Met -ATS-> amino-cyclopropanone carboxylic acid -ACO (O2->CO2) -> ethylene
47
Acclimation
- ethylene pretreatment = increased hypoxia tolerance
- ethylene + hypoxia-induced phytoglobin can scavenge NO (uses O2 as substrate)
48
How are phytoglobins induced?
By ethylene
49
Ethylene induces ERFVII stabilisation
- CPTIO = NO scavenging partner
- does not accumulate in ethylene treated A. thaliana roots
- stabilises RAP2.13
50
ANACO13
- early response TF
- hypoxia-induced via promotors
- homologs: -16, -17
51
Membrane-associated NAC-TFs
- ANACO13: ER-localised
- cleaved under mitochondrial stress
- goes to nucleus
52
What cleaves ANACO13?
- chemical mutagenesis analysis
- rhomboid proteases cleave substrates inside membranes
- rbl6/rbl2: no ANACO13 nuclear relocalisation
53
Does ANACO13 contribute to hypoxia tolerance?
silencing/ inhibiting ER release using artificial miRNAS results in < hypoxia tolerance + bleaching
