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Drought Stress II Flashcards

1
Q

Long term responses

A

Water balance (source-sink relations)

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2
Q

Water balance

A
  • inducing water uptake
  • hydraulic accumulation
  • reducing water loss
  • drought escape
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3
Q

Induction of water uptake

A

1) increased primary root growth
2) root tropisms and patterning towards water

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4
Q

Hydraulic acclimation

A
  • decreased xylem diameter
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5
Q

Decreased water loss

A
  • increased epidermal wax production
  • leaf abscission
  • decreased stomatal density
  • decreased leaf surface
  • decreased shoot growth
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6
Q

Drought escape

A
  • induction of reproductive phase transition
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7
Q

ABA alters xylem development

A
  • endodermal ABA signalling inhibits metaxyken formation
  • protoxylem
  • miRNA165/166
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8
Q

Protoxylem

A
  • smaller
  • carries < water
  • less embolism
  • thinner cell walls
  • ^ water entry - embolised vessels when drought subsides
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9
Q

Suberisation

A

Protected inner cell layers (vasculature)

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10
Q

Suberin

A
  • Hydrophobic biopolymer
  • insulates
  • minimised water loss
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11
Q

ABA induces endodermal suberisation

A
  • GPAT6 -> C16 Suberin biosynthesis
  • stronger in Arabidopsis accession from drier environments
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12
Q

Water flow is affected by root architecture

A

And root architecture affects water flow

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13
Q

Optimal root architecture depends on

A

1) soil type
2) water depth
3) nutrient distribution
4) micro-organisms

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14
Q

Important root traits

A

1) primary root length(s)
2) lateral root density, elongation and angle
3) crown/adventitious roots
4) osmotropism

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15
Q

Drought induced root growth strategies

A

1) xerotropism
2) hydrotropism
3) xerobranching
4) hydropatterning

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16
Q

Xerotropism

A
  • primary root growth
  • deeper and moister soil
  • enhanced gravitropism
  • increased auxin sensitivity
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17
Q

Hydrotropism

A
  • growth reorientation towards water
  • ABA-mediated
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18
Q

Hydrotropism expts

A

1) ABA signalling in cortex
2) gravitropism feedback inhibition
3) ABA-mediated differential elongation in cortex ; drives “bending”
- split agar hydrotropism assay

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19
Q

Xerobranching

A
  • repression of lateral root formation in air-filled soil
  • ABA
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20
Q

Hydropatterning

A
  • formation of lateral roots on the side w moister soil
  • auxin
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21
Q

Reducing water loss

A
  • decrease shoot growth, leaf surface and stomatal density
  • increase epidermal wax and senescence
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22
Q

Enhanced water absorption

A
  • increased root growth
  • requires resource allocation
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23
Q

If drought stimulus is severe enough,

A

All resources are allocated to meristems for preservation (growth arrest)

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24
Q

Drought escape

A
  • accelerate reproductive phase
  • early flowering
  • ABA-mediated photoperiodic floral induction
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25
No stress flowering
1) inductive photoperiod 2) circadian clock + light 3) kinase + TF regulation 4) Florigen accumulation 5) apex = flowering
26
Drought escape mechanism
Non-inductive photoperiod hijacked by ABA
27
How to help agriculture combat drought?
- technology - biology
28
Monitoring methods
- inform management practices - efficient water utilisation
29
Soil monitoring + improved irrigation practices
1. Soil humidity sensors 2. Drip irrigation 3. Partial root-zone drying
30
Partial root-zone drying
- plants are watered on alternating sides; the each half of the root system alternates: wet/dry - often results in equivalent harvests - smaller leaf sizes
31
Partial root-zone drying hypothesis
- wet roots: hydrate shoot - dry roots: partial stomatal closure; water conservation
32
Plant monitoring
1) thermal imaging: drones/satellites (aerial) 2) generate drought maps 3) precision farming
33
How does plant monitoring work?
1) drought 2) stomatal closure 3) decreased transpiration 4) increased leaf surface temperature detected in IR 5) irrigate that patch!
34
Photosynthesis-related measurements
- GE - chlorophyll fluorescence - inform plant water status; stress responses
35
Using biology to combat drought
1) osmotic adjustment 2) stomata conductance regulation 3) water use efficiency ^ 4) photosynthetic rate ^ 5) delayed senescence 6) root architecture 7) reproductive phase regulation
36
Strategies for using biology to combat drought:
1) chemical application: osmoprotectants, growth effectors 2) induce drought memory: seed priming 3) generate drought-tolerant varieties: molecular breeding and genetic engineering
37
Stress priming
In seeds, seedlings, plants
38
Osmopriming
- osmolytes + antioxidant accumulation - plant-water relations - root architecture depends
39
Osmopriming had improved drought tolerance in
1) wheat 2) barley 3) sorghum 4) caraway
40
Genetic strategies
- identify relevant genes, then manipulate them
41
Osmotic adjustments
- mannitol - proline - glycine betaine
42
Protective proteins
- chaperones - dehydrins
43
Transport proteins
- vascular Na+/K+ antiporter - aquaporins
44
Forward genetics
- phenotype -> gene - mutant/natural variant carries particular phenotype - identify gene: mapping, sequencing, validation - (elucidate corresponding protein function)
45
Reverse genetics
- gene -> phenotype - specific gene of unknown function - phenotype analysis on corresponding mutations shy - elucidation of corresponding protein function
46
Process of identifying relevant gene by reverse genetics
1. Gene X = drought-induced, highly conserved across species 2. Hypothesis: Gene X contributes to drought tolerance 3. Inactivate + OX 4. Compare performance to confirm hypotheses
47
Considerations when identifying relevant genes
- does it work similarly in crop of interest? - field conditions? - GMO? - drawbacks?
48
CspA/B maize
- bacterial RNA chaperone - increased yields in maize under late-season drought - no growth penalty under normal conditions
49
Maize GE
- bacterial cold shock proteins - decreased senescence, increased photosynthesis and chlorophyll
50
Soybean GE
- Hahb4 - decreased senescence - increased photosynthesis
51
Hahb4
stress-inducible (via ethylene sensitivity) HD-ZIP TF
52
T6P
- impacts sink strength - ability to import, assimilate and use - insulin/like
53
How does T6P work: reaction sequence
hexose-P -TPS-> T6P -TPP-> trehalose
54
How does T6P work: consequences
- activated by sucrose - activated biosynthesis, respiration, growth - blocks photosynthesis, starch and other C source anabolism
55
OX TPP in developing ears
- low T6P: “starvation” - sucrose import - increase yield - in control and drought conditions
56
Breeding approaches
- wild populations have greater genetic diversity - many ancestral traits are not represented in modern varieties - can still be found in germplasm collections
57
Conventional breeding
- v. long, tedious - phenotype-based - genotype changes unknown - requires germplasm diversity
58
How does conventional breeding work ?
- breed high yielders + drought-resistant plants - search for progeny combining both parental traits
59
Molecular breeding
- genotype based, via molecular markers - QTL linked to trait(s) - mapping and GWAS - no GMO; minimal genome change - no need to phenotype; locus identifies trait - proceed only w relevant plants: highest % of relevant loci
60
Gene editing
- if you know causal gene/mutation - highly precise, flexible, fast
61
Examples of gene editing for drought
- maize ARG058 - tomato SINPRI - Arabidopsis AREB1 - rice OSSAPK2
62
How does gene editing work
1) DNA modification within plant cells 2) minimal genome changes and selection time 3) inducible, cell-type specific modifications minimise trade offs

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