Xinguang Zhu1,2
1.Plant Systems Biology Group, Partner Institute of Computational Biology, Chinese Academy of Sciences/Max
Planck Society
2. Institute of Genomic Biology, University of Illinois at Urbana Champaign
Options to engineer higher photosynthetic energy conversion
efficiency
Solar Biofuels from Microorganisms
Road Map
The rationale behind increasing energy conversion efficiency
Realizing the maximal energy conversion efficiency
Maintaining the energy conversion efficiency
Wh =
Harvested yield
S
Total solar energy
i
Interception efficiency
c
Conversion efficiency
Partitioning efficiency
What determines harvested yield?
Monteith (1977) Philosophical Transactions of the Royal Society of London
For modern
cultiv
ars of th
e major f
ood crops
i = 90% an
d = 60%; but c
= ca. 0.5%
Zhu et al (2008) Current Opinion in Biotechnology4.6% 6%
What c is achieved in the field?
The highest c over a whole growing season: C3: 2.4% C4: 3.7%
Common c over a whole growing season: < 0.5%
Reviewed in: Zhu et al (2008) Current Opinion in Biotechnology
e-P
lant
conce
pt
Photosynthetic energy conversion efficiency
Long et al (1994) ARPPPMB
Realizing the maximal energy conversion efficiency
Nitrogen redistribution in the photosynthetic carbon metabolism
Manipulations of Rubisco kineticsDesign new pathwayTransforming C3 photosynthesis
into C4 photosynthesis
Sink
KG
O2
PGA
PGCA
GCA
GCA
GOA
GLYSER
HPRGLU
O2
H 2O2
GCEA
GCEA
111
112
121
122
123
113
124
NAD
NADH
Pi
ATP
ADP
GLY + NAD +CO 2 + NADH
131
101
GOA
GLY
KG
O2
PGA
PGCA
GCA
GCA
GOA
GLYSER
HPRGLU
O2
H 2O2
GCEA
GCEA
111
112
121
122
123
113
124
+
NA
Pi
ATP
ADP
GLY + NAD +CO 2 + NADH
131
Stroma
Cytosol, mitochondria, and peroxisome
GOA
GLY
RUBP
CO 2
PGA + PGA
1
DPGA
ATP
ADP
GAP
NADPH +HNADP+Pi2
GAPGAPGAP DHAP
DHAP
FBP
PiF6P
34
5
6
7Xu5PE4P
8
SBP
S7P
9
Xu5PRi5P
10
Ru5PRu5P Ru5P
G6P21
G1P
ADPG
22
ATP
PPi
23Pi
Starch
25
11 12
12
ATP ADP
Pi Pi
Pi
PGA
Pi
31 32
GAP
33
Pi
Pi
DHAP
Pi
DHAP
RUBP
CO 2
PGA + PGA
1
DPGA
ATP
ADP
GAP
NADPH +HNADP+Pi2
GAPGAPGAP DHAP
DHAP
FBP
PiF6P
34
5
6
7Xu5PE4P
8
SBP
S7P
9
Xu5PRi5P
10
Ru5PRu5P Ru5P
G6P21
G1P
ADPG
22
ATP
PPi
23Pi
Starch
25
11 12
12
13
ATP ADP
Pi Pi
Pi
PGA
Pi
31
GAP
Pi
Pi
DHAP
Pi
DHAP
OP
UTP OPOP 2OP
ATP
ADP
OP
FBP F6P G6P G1P UDPGlu
SUCP SUC
53 54
55
56
57
58 59
52
F26BP
F6P
UDP
60
UDP
61
Sink
62
55
61
101
Model of carbon metabolism
Drawn based on Zhu et al (2007) Plant Physiology 145: 513-526
Algorithms for building dynamic systems models
Establish the reaction diagram
NoAlgorithm ?
Yes
Yes Finished
Realistic ?Numerical experiments
Yes
Stable Solution ?
Solve the system of ODEs
Develop the ordinary differential equations (ODE)
Construct the rate equations
No
No
Drawn based on Zhu et al (2007) Plant Physiology 145: 513-526
Validations
Zhu et al (2007) Plant Physiology
Evolutionary algorithm at work
Ph
oto
syn
the
sis
Ru
bis
co GA
PD
HF
BP
a
ldo
lase FB
Pa
se
Tra
nsk
eto
lase
Ald
ola
se SB
Pa
seP
RK
AD
PG
PP
PG
CA
Pa
seG
OA
O
xid
ase
HP
R
red
uct
ase
GG
AT
GD
CcF
BP
a
ldo
lase cF
BP
as
e UD
PG
PS
PS S
PP
F2
6B
Pa
se
PG
A K
ina
se
GC
EA
K
ina
se
GS
AT
100
0
200
300
400%
of
beg
inn
ing
Zhu et al (2007) Plant Physiology
Theoretical optimal concentrations of enzymes in carbon metabolism
Zhu et al (2007) Plant Physiology
Raines (2003) Photosynthesis Research
Zhu et al (2004) Plant Cell Environ
Steady State Photosynthesis Model
Light
RuBP-limited PhotosynthesisCO2
uptake
Rubisco-limited Photosynthesis
kcc
Farquhar et al (1980) Planta
CO2 + H2O + Light Energy CH2O + O2
CO2 concentration (mol mol-1)
150 200 250 300 350
Op
tim
al s
pec
ific
ity
(
70
80
90
100
110
120Jmax 110
Jmax 250
Jmax 180
Fitted curve for Jmax 250
1
C1
2
C2
Zhu et al (2004) Plant Cell Environ
IPCC 2001
http://www.biochimie.univ-montp2.fr/licence/qabs/alfa_beta/tonneau/rubisco/rubisco_rub10.gifRubisco
Species Ac'
(mmol m-2 day-1)
Ac'
(% increase)
Asat
(mol m-2 s-
1)Current average C3
crop(kc
c = 2.5, = 92.5)
1040
0
14.9
Griffithsia monilis (kc
c = 2.6, = 167)
1430
27
21.5
Amaranthus edulis(kc
c = 7.3, = 82)
1250
17
28.3
Amaranthus edulis/current
(kcc = 7.3, = 82)
(kcc = 2.5, = 92.5)
1360
31
28.3
Zhu et al (2004) Plant Cell Environ; Long et al (2006) Plant Cell Environ
Kebeish et al 2007 Nature
New Pathways Design
Engineering photorespiratory bypass leading to substantial increase in photosynthesis
1. The saving of ATP from decreased release of NH4
+
release did not contribute to the increase in photosynthesis.
2. Releasing CO2 in chloroplast is key to successfully engineer photorespiratory bypass.
Kebeish et al 2007 Nature
Maintaining Efficiency
Photo-protection
Temperature Stresses
Water stress
Photoprotective state changes light response curve
Light Level
Non-Photoprotective
Photoprotective
CO
2 u
pta
ke Asat
Light
CO
2 u
pta
ke
Asat
High Light
Low Light
Time (minute)
0 1 2 3 4 5 6 7 8
PPFD
( m
ol m
-2 s
-1)
0
500
1000
1500
2000
Dynamic LightAverage of the dynamic light
Light Level
A
12% ↓
0.2% ↓
Case 1
Case 2
The Reverse Ray Tracing AlgorithmZhu et al (2004) J. Exp. Botany
0
500
1000
1500
2000
2500
Q ( m
ol
m-2 s
-1)
0
500
1000
1500
2000
2500
0 4 8 12 16 20 24
Layer 2
Layer 4 Layer 8
Time (Hour)0 4 8 12 16 20
0
500
1000
1500
2000
2500Layer 10 Layer 12
Layer 1
Zhu et al (2004) J. Exp. Botany
Chilling Tolerant
Per
cen
t d
ecre
ase
in
Ac
0
5
10
15
20
25
30
35
10 o
C
20 o
C
30 o
C
Chilling Susceptible
Zhu et al (2004) J. Exp. Botany
Options to engineer higher photosynthetic energy conversion
efficiency (c)Alteration % increase
in ec
Speculated Time
Horizon (yr)
Ref
Improved canopy architecture10% (0-40%) 0-10
Long et al
(2006)
Rubisco with decreased
oxygenase activity 30% (5-60%) ???Zhu et al
(2004 a)
Increased rate of recovery from
photoprotection of
photosynthesis15% (6-40%) 5
Zhu et al
(2004 a)
Introduction of higher catalytic
rate foreign forms of Rubisco 22% (17-30%) 5-10Zhu et al
(2004 b)
Altered allocation of resources
within photosynthetic apparatus 30% (0-60%) 0-5Zhu et al
(2007)
Efficient C4 photosynthesis
engineered into C3 crops30% 15-30
Zhu et al
(2008)
Why hasn’t evolution already maximized photosynthetic production ?
Wild plants versus designed crops (1)
25 oC
Well watered
The
Calvin Cycle
The Calvin
Cycle
Photo-respiratory
pathway
Photo-respiratory
pathway
Beginning leaf Designed final leaf
Wild plants versus designed crops (2)
45 oC
Drought
The
Calvin Cycle
The Calvin
Cycle
Photo-respiratory
pathway
Photo-respiratory
pathway
Beginning leaf Designed final leaf
Wild plants versus designed crops (3)
Having high photosynthesis
Investment to ensure survival under extreme but rare stress
Wild Plants
Not critical Critical
Designed Crops
Critical Not critical
Systems Biology and Synthetic Biology
Synthetic Biology: New pathway design, new genetic regulatory network design , redesign existing parts, devices, systems etc
… …
Systems Biology: Resource use efficiency, optimality, plasticity, environmental stochasticity and heterogeneity, genetic constraints
… …Mathematical
Models
+ Evolutionary algorithms
ConclusionsThere is much potential to further
increase energy conversion efficiency. The photosynthetic energy conversion
efficiency can be increased by both realizing the maximal energy conversion efficiency and maintaining higher energy conversion efficiency under stress conditions.
It is time now to use rationale design to engineer higher photosynthesis.
ACKNOWLEDGEMENTS
CollaboratorsProf. Steve Long (Plant Biology/UIUC)Prof. Donald Ort (Plant Biology/UIUC)Prof. Archie Portis (Plant Biology/UIUC)Prof. Eric de Sturler (Math/VT)Prof. Govindjee (Plant Biology/UIUC)
PICBVincent DevlooDanny TholenGuiLian ZhangFuQiao Xu
LinYing LuCaroline TholenChangPeng XinYuJing SunXin Yan
Li KaiChang Xiao HongBo LeiRomanSU