Improving radiation use efficiency in
tropical rice
Erik Murchie
Agricultural & Environmental
Sciences
This talk
1. Radiation use efficiency (RUE) in tropical rice
2. Photosynthesis and RUE in the field.
3. Improvement of RUE: ways forward
Transcriptomics of light-responses
Transgenic rice
Mutant screening
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•
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Rice farming is the single largest use of land for food
90 % of this is in Asia
Only 6 – 7 % of all rice is exported from country of origin
Rice forms around 60 % of daily calories for half the world’s
population
• It is the single largest source of food, employment and
income for the world’s poor
• IRRI estimate 40-50 % increase in grain yields ha-1 in next
30 years. Large part of this must come from irrigated rice in
Asia, if water supplies are maintained.
• Genome sequenced.
Rice Almanac (2002): IRRI, CIAT, FAO
Stagnation of rice yield potential
in the tropics
Year
World rice
production
Tg
Asian irrigated rice
production area
yield
Tg
t ha-1
1995
2025
Difference
534
800
266
375
641
266
1966 : Yield potential of IR8 was
1999 : Yield potential of IR72 is
75
75
0
5
8.5
3.5
9 - 10 t ha-1
9 - 10 t ha-1
Peng et al (1999) Crop Science 39,1552
Radiation use efficiency
Biomass produced per unit radiation
intercepted or absorbed
700
Bambara groundnut 2006
600
500
Accumulated
AG Dry weight
400
300
200
100
0
0
100
200
300
400
500
600
700
Cumulative intercepted radiation
• Vegetative growth is proportional to intercepted radiation (Monteith 1977)
• RUE is critical in situations where biomass production is limiting yield.
Radiation use efficiency as a target
for yield potential improvement
Radiation
Conversion
Factor
(g dry matter MJ-1)
Max. Grain Yield (t ha-1)
Tropics 110d
Temperate
2.2 (rice)
2.7 (wheat)
3.3 (maize)
10.0
12.3
15.0
15.0
18.4
22.5
(12.3)
Mitchell, Sheehy, Woodward (1998) IRRI discussion paper 32
Radiation use efficiency
g DM MJ-1 intercepted PAR
Mitchell et al (1998)
• Growth stage
• Above ground and below ground
• Absorbed radiation or intercepted radiation?
Radiation use efficiency
• Why does this ceiling (12.5 t ha-1) occur for tropical rice?
– Combination of leaf and canopy factors
– 15 t ha-1 impossible with current C3 photosynthesis
• Is rice efficient at capturing light energy and converting it
into biomass?
• What are the routes forward for improvement of radiation
use efficiency?
Leaf factors
Eliminating photorespiration in tropical rice would improve
RUE by 31 %
Rice with C4 characteristics (IRRI priority)
Kranz anatomy or single cell ?
Rubisco engineering
Improvement of photosynthetic capacity
Rice already has one of the highest of any C3 species
(30-40 μmol CO2 m-2 s-1)
Improvement of dynamic responses of photosynthesis
Diurnal variation in light-saturated
photosynthesis
30
0.6
25
-2 -1
g (mols m s )
-2 -1
CO2 Assimilation(μmols m s )
60 days
20
15
10
0.5
0.4
0.3
0.2
5
0.1
0
0.0
6
8
10
12
14
16
18
6
8
10
12
14
16
18
Time of day (hours)
Time of day (hours)
Mid-day depression of photosynthesis (light-saturated photosynthetic rate)
Dry season, optimal conditions (irrigated, fertilised etc)
Murchie et al (1999) Plant Physiology, 119, 553-563.
‘Mid-day depression’ of photosynthesis in five
cultivars of rice at two locations in the Philippines
40
Photosynthesis
(μmol CO2 m-2 s-1)
35
30
25
20
15
10
5
0
0
500
1000
1500
2000
Light intensity (μmol m-2 s-1)
Causes:
Stomatal closure due to e.g. high vapour pressure deficit
Photoinhibitory damage / down-regulation of light reactions
Carbohydrate accumulation and feedback
Radiation capture and use in rice :
leaf and canopy processes
1000 μmol m-2 s-1
Rate of Excitation in
leaf or canopy
2500
2000
Un-used excitation
PPFD
1500
Rate of Photosynthesis
in leaf or canopy
1000
Used excitation
500
0
6
8
10
12
14
16
Tim e of D ay (hrs)
18
Light Intensity
Light-saturation and photoinhibition of
photosynthesis in the field
0.8
0.7
0.6
φPSII
0.5
0.4
0.3
0.2
0.80
0.75
Fv/Fm
0.70
0.65
6
8
10
12
14
16
18
Time of day (hrs)
Murchie et al (1999) Plant Physiology, 119, 553-563.
Can the slow recovery of φCO2 affect
canopy photosynthesis ?
photosynthesis
Photoinhibition
(slow recovering φCO2)
light intensity
Modelling using ray-tracing algorithms at a temperature of 30 oC
predicts a reduction in canopy photosynthesis of 17 %.
(Zhu, Ort, Whitmarsh, Long (2004), Journal of Experimental Botany 55,
1167-1175)
Current approaches
1. Canopy level assessment using transgenic rice.
Slow recovery of φCO2 (‘photoinhibition’)
and resilience to rapid temperature alterations
Collaboration with Peter Horton and Syngenta
2. Screening of IR64 deletion mutant collection for altered
photosynthetic properties.
3. Analysis of photosynthesis in historical IRRI cultivars
Rice transformants
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•
•
•
Arabidopsis ChyB
Rice PsbS
Rice Lhcb1
Rice Pgr5
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•
•
•
RNAi rice ChyB
RNAi rice PsbS
RNAi rice Lhcb1
RNAi rice Pgr5
Induced on
response to
high light
treatment
microarray
studies
Manipulating light-harvesting and
photoprotection in rice
ChyB
β-carotene
Xanthophyll cycle
pool
Zeaxanthin
Protection of
membrane
lipids
NPQ
PsbS
Energy dissipation
‘photoinhibition’
Lowered φCO2
Dynamic light use efficiency:
the genes involved
PsbS
22 kDa thylakoid protein.
A key regulator in the switch between light harvesting and
the dissipation of excess (harmful) energy.
PsbS
Light harvesting state
Dissipative state
(reduced φCO2)
Its not just a switch ! The amount of dissipation and the
kinetics of formation and relaxation are determined
quantitatively by the level of PsbS protein.
irradiance
1. Empirical determination of
the effect of energy
dissipation within rice
canopies.
2. Manipulation of the
dissipative state using rice
depth
plants with varying PsbS
and ChyB levels and
measure the effects on
canopy photosynthesis
(modelled and measured)
3. The role of fluctuating and
‘constant’ irradiance levels
(A.thaliana).
hrs
Overexpression of β-carotene hydroxylase
(ChyB) in Arabidopsis thaliana
β- carotene
Davison et al , Nature (2000)
200
180
160
140
120
100
80
60
40
20
0
350
Violaxanthin
300
250
200
150
100
50
0
LL ML LL ML LL ML LL ML
C24
ChyB
Overexpression of ChyB in A.thaliana confers
higher resistance to high temperature and high
irradiance
Multiple stress treatment :
14 days at 1000 μmol m-2 s-1 , 35 oC / 18 oC (day / night)
ChyB overexpressors
WT
Overexpression of ChyB in A.thaliana confers
higher resistance to low temperature and high
irradiance
sChyB 8.31
sChyB 8.29
WT
Matt Johnson (Sheffield), Michel Havaux (Cadarache)
Luminescence imaging of lipid
peroxidation in vivo
Matt Johnson (Sheffield) , Michel Havaux (Cadarache)
Work to date
• 14 lines of rice transformed with cAtBCH
(Arabidopsis ChyB) grown under typical rice
conditions
• Analysed by HPLC for changes in
violaxanthin/neoxanthin ratio
• PCR analysis for presence of selectable
marker gene
• 10 out of 14 lines show elevated (max x2)
levels of violaxanthin compared to expected
wt levels
Car/chl (rel)
Carotenoid composition of transformed
rice
50
45
40
35
30
25
20
15
10
5
0
OE ChyB
wt
RNAi ChyB
B-car
lutein
neoxanth
Carotenoid
XC
Screening of the IR64 deletion mutant
collection
Forward screening of rice mutant collections is difficult
for practical reasons.
The IR64 deletion mutant collection at IRRI has 50,000
independent lines at the M4 stage.
We have identified 1300 lines from the iris.irri.org
database which have altered leaf shape.
We are screening these for a number of characters:
leaf thickness
leaf area
mesophyll cell size and arrangement
chloroplast number and size
IRRI has released over 40 cultivars
since 1966
40
Pmax
30
(μmol CO2 m-2 s-1)
20
10
0
stomatal
condictance
(mol H20 m-2 s-1)
1.0
0.8
0.6
0.4
0.2
IR
IR 8
2
IR 0
2
IR 2
4
IR 0
4
IR 2
4
IR 5
5
IR 4
6
IR 8
7
PS N 2
BRPT
C2
0.0
Peng et al (1999) Crop Science 39,1552)
Underlying trends in historical IRRI cultivars?
500
40
450
Pmax
35
n.s.
400
s.s.
n.s.
30
s.s.
350
25
300
20
250
15
200
0.65
2.4
2.2
n.s.
s.s.
qp
s.s.
n.s.
0.55
2.0
Rubisco
0.60
s.s. -significant to 5 % l
n.s. - not significant
Total Chlorophyll
45
1.8
0.50
1.6
1.4
0.8
9
0.7
n.s.
8
s.s.
0.6
s.s.
n.s.
7
0.5
6
0.4
19
65
19
70
19
75
19
80
19
85
19
90
19
95
20
00
5
19
65
19
70
19
75
19
80
19
85
19
90
19
95
0.3
Year of Cultivar Release
Total protein
stomatal conductance
0.45
Acknowledgements
• IRRI
• Uni. of
Sheffield
ChyB Work
Shaobing Peng
Yizhu Chen
John Sheehy
Jianchang Yang
Peter Horton
Stella Hubbart
Matt Johnson
Sveta Solovieva
Tong Zhu
Paul Davison, Neil Hunter (Sheffield),
M.Havaux (Cadarache)