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
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2
Q

Water logging

A

Only the below-ground part is under water saturating conditions

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3
Q

Flooding

A

Partial and complete submergence

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4
Q

Partial submergence

A

Root system and portion of shoot underwater

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5
Q

Complete submergence

A

Whole plant covered

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6
Q

Economic impact of crop flooding

A

Largest stressor!

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7
Q

Dynamics of flooding events

A
  • intensity, timing, duration = changing
  • frequent: UK, CE, Balkan area
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8
Q

Why is submergence a stress to plants?

A
  • anoxia
  • anaerobic activity of roots and rhizosphere
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9
Q

ROS

A
  • affect mitochondria and chloroplasts
  • < photosynthesis
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10
Q

Submergence process:

A
  1. Soil redox potential «
  2. Accumulation of toxic compounds (Mn2+, Fe2+, H2S)
  3. Gases diffuse 10^4 slower in water than air (severely &laquo_space;O2, CO2 availability; ethylene entrapment)
  4. Fermentation
  5. Carbon starvation
  6. &laquo_space;photosynthesis
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11
Q

Anaerobic metabolism

A
  • fermentations necessary to replenish glycolysis NAD+
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12
Q

Fermentation process

A
  1. Starch -> soluble sugars
  2. Soluble sugars -(glycolysis)-> pyruvate (NAD+ -> NADH; ADP -> ATP)
  3. Pyruvate -lactate dehydrogenase-> lactate (toxic! Acidifies, damages cell) (NADH -> NAD+)
    OR
  4. Pyruvate -pyruvate decarboxylase-> acetylaldehyde (toxic!)
  5. Acetylaldehyde -alcohol dehydrogenase-> ethanol (preferred!) (NADH -> NAD+)
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13
Q

Phytoglobins

A
  • plant Hbs
  • v high O2 affinity
  • no long distance transport
    • nitrate reductase: NAD+ regeneration
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14
Q

Nitrite

A

Alternative e- acceptor in mETC

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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
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16
Q

N-degron pathway

A

Determines protein (in)stability depending on exposed aas

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17
Q

Oxygen-dependent oxidation of N-terminal cysteine (+R)

A

Prepares proteins for degradation

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18
Q

Cysteine in 2nd position

A
  • dangerous!
  • exposure R residue; degradation signal
  • PTM + R
  • 4x possible pathways
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19
Q

N-degron 4x pathway 1

A
  1. MC -MetAP-> C
  2. C -> *C
  3. *C -> RC
  4. RC -NO-> degradation
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20
Q

N-degron pathway 2

A
  1. MC -> NQ
  2. NQ -NTAN/NTAQ-> DE
  3. DE -ART6/VBR1-> R
  4. R-Ub-> degradation
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21
Q

N-degron pathway 3

A
  1. MC -endoproteolytic cleavage-> DE
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22
Q

N-degron pathway 4

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