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B3.0 > Drought Stress II > Flashcards

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
Q

No stress flowering

A

1) inductive photoperiod
2) circadian clock + light
3) kinase + TF regulation
4) Florigen accumulation
5) apex = flowering

26
Q

Drought escape mechanism

A

Non-inductive photoperiod hijacked by ABA

27
Q

How to help agriculture combat drought?

A
  • technology
  • biology
28
Q

Monitoring methods

A
  • inform management practices
  • efficient water utilisation
29
Q

Soil monitoring + improved irrigation practices

A
  1. Soil humidity sensors
  2. Drip irrigation
  3. Partial root-zone drying
30
Q

Partial root-zone drying

A
  • 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
Q

Partial root-zone drying hypothesis

A
  • wet roots: hydrate shoot
  • dry roots: partial stomatal closure; water conservation
32
Q

Plant monitoring

A

1) thermal imaging: drones/satellites (aerial)
2) generate drought maps
3) precision farming

33
Q

How does plant monitoring work?

A

1) drought
2) stomatal closure
3) decreased transpiration
4) increased leaf surface temperature detected in IR
5) irrigate that patch!

34
Q

Photosynthesis-related measurements

A
  • GE
  • chlorophyll fluorescence
  • inform plant water status; stress responses
35
Q

Using biology to combat drought

A

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
Q

Strategies for using biology to combat drought:

A

1) chemical application: osmoprotectants, growth effectors
2) induce drought memory: seed priming
3) generate drought-tolerant varieties: molecular breeding and genetic engineering

37
Q

Stress priming

A

In seeds, seedlings, plants

38
Q

Osmopriming

A
  • osmolytes + antioxidant accumulation
  • plant-water relations
  • root architecture depends
39
Q

Osmopriming had improved drought tolerance in

A

1) wheat
2) barley
3) sorghum
4) caraway

40
Q

Genetic strategies

A
  • identify relevant genes, then manipulate them
41
Q

Osmotic adjustments

A
  • mannitol
  • proline
  • glycine betaine
42
Q

Protective proteins

A
  • chaperones
  • dehydrins
43
Q

Transport proteins

A
  • vascular Na+/K+ antiporter
  • aquaporins
44
Q

Forward genetics

A
  • phenotype -> gene
  • mutant/natural variant carries particular phenotype
  • identify gene: mapping, sequencing, validation
  • (elucidate corresponding protein function)
45
Q

Reverse genetics

A
  • gene -> phenotype
  • specific gene of unknown function
  • phenotype analysis on corresponding mutations shy
  • elucidation of corresponding protein function
46
Q

Process of identifying relevant gene by reverse genetics

A
  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
Q

Considerations when identifying relevant genes

A
  • does it work similarly in crop of interest?
  • field conditions?
  • GMO?
  • drawbacks?
48
Q

CspA/B maize

A
  • bacterial RNA chaperone
  • increased yields in maize under late-season drought
  • no growth penalty under normal conditions
49
Q

Maize GE

A
  • bacterial cold shock proteins
  • decreased senescence, increased photosynthesis and chlorophyll
50
Q

Soybean GE

A
  • Hahb4
  • decreased senescence
  • increased photosynthesis
51
Q

Hahb4

A

stress-inducible (via ethylene sensitivity) HD-ZIP TF

52
Q

T6P

A
  • impacts sink strength
  • ability to import, assimilate and use
  • insulin/like
53
Q

How does T6P work: reaction sequence

A

hexose-P -TPS-> T6P -TPP-> trehalose

54
Q

How does T6P work: consequences

A
  • activated by sucrose
  • activated biosynthesis, respiration, growth
  • blocks photosynthesis, starch and other C source anabolism
55
Q

OX TPP in developing ears

A
  • low T6P: “starvation”
  • sucrose import
  • increase yield
  • in control and drought conditions
56
Q

Breeding approaches

A
  • wild populations have greater genetic diversity
  • many ancestral traits are not represented in modern varieties
  • can still be found in germplasm collections
57
Q

Conventional breeding

A
  • v. long, tedious
  • phenotype-based
  • genotype changes unknown
  • requires germplasm diversity
58
Q

How does conventional breeding work ?

A
  • breed high yielders + drought-resistant plants
  • search for progeny combining both parental traits
59
Q

Molecular breeding

A
  • 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
Q

Gene editing

A
  • if you know causal gene/mutation
  • highly precise, flexible, fast
61
Q

Examples of gene editing for drought

A
  • maize ARG058
  • tomato SINPRI
  • Arabidopsis AREB1
  • rice OSSAPK2
62
Q

How does gene editing work

A

1) DNA modification within plant cells
2) minimal genome changes and selection time
3) inducible, cell-type specific modifications minimise trade offs

B3.0 (23 decks)

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