Xinguang Zhu1,2

1
Options to engineer higher photosynthetic energy
conversion efficiency

• 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

Solar Biofuels from Microorganisms
2
Road Map

• The rationale behind increasing energy conversion
  efficiency
• Realizing the maximal energy conversion
  efficiency
• Maintaining the energy conversion efficiency

3
What determines harvested yield?
Wh
For modern cultivars of the major food crops ?i
90 and ? 60 but ?c ca. 0.5
Harvested yield
Monteith (1977) Philosophical Transactions of the
Royal Society of London
4
6
4.6
Zhu et al (2008) Current Opinion in Biotechnology
5
What ec is achieved in the field?

• The highest ec over a whole growing season
• C3 2.4
• C4 3.7
• Common ec over a whole growing season
• lt 0.5

Reviewed in Zhu et al (2008) Current Opinion in
Biotechnology
6
e-Plant concept
7
Photosynthetic energy conversion efficiency
Long et al (1994) ARPPPMB
8
Realizing the maximal energy conversion efficiency

• Nitrogen redistribution in the photosynthetic
  carbon metabolism
• Manipulations of Rubisco kinetics
• Design new pathway
• Transforming C3 photosynthesis into C4
  photosynthesis

9
Model of carbon metabolism
13
Ru5P
Ru5P
Ru5P
Ru5P
Ru5P
Ru5P
ATP
ADP
ATP
ADP
11
12
11
12
Xu5P
Ri5P
Xu5P
Ri5P
10
10
Starch
Starch
S7P
S7P
12
12
Pi
Pi
9
25
9
25
PPi
PPi
Pi
Pi
RUBP
RUBP
SBP
SBP
Stroma
23
23
CO
CO
8
8
2
2
ATP
ATP
Xu5P
E4P
ADPG
Xu5P
E4P
ADPG
O
O
2
2
1
1
7
7
G1P
G1P
111
111
22
22
PGCA
PGCA
21
21
F6P
G6P
F6P
G6P
PGA PGA
PGA PGA
Pi
Pi
6
6
PGA
PGA
ATP
ATP
112
112
FBP
FBP
2
2
ADP
ADP
5
5
GAP
GAP
DHAP
GAP
GAP
DHAP
NADPH
NADPH
Pi
Pi
H
NADPPi
H
NADPPi
113
113
ADP
ADP
GAP
DHAP
GAP
DHAP
ATP
ATP
DPGA
DHAP
DPGA
DHAP
GAP
GAP
GCA
GCA
4
4
3
3
GCEA
GCEA
Pi
Pi
Pi
Pi
Pi
Pi
101
31
32
33
31
101
Pi
Pi
GCEA
GCEA
GCA
GCA
Pi
Pi
Pi
Pi
O
O
Sink
GAP
DHAP
GAP
DHAP
2
2
NADH
NA
PGA
PGA
121
121
123
123
H
O
H
O
2
2
2
2

NAD
OP
GOA
GOA
HPR
HPR
57
SUCP
F6P
SUC
GLY
GLY
GLU
GLU
122
122
124
124
62
56
KG
KG
GOA
GOA
53
54
52
Sink
FBP
F6P
G6P
G1P
UDPGlu
SER
SER
GLY
GLY
UDP
131
131
UDP


GLY NAD
GLY NAD
CO
NADH
CO
NADH
2
2
OP
ATP
55
55
58
59
60
61
61
OPOP
2OP
UTP
ADP
Cytosol, mitochondria, and peroxisome
F26BP
Drawn based on Zhu et al (2007) Plant Physiology
145 513-526
10
Algorithms for building dynamic systems models
Establish the reaction diagram
Drawn based on Zhu et al (2007) Plant Physiology
145 513-526
11
Validations
Zhu et al (2007) Plant Physiology
12
Evolutionary algorithm at work
400
of beginning
300
200
100
0
PGA Kinase
Photosynthesis
HPR reductase
GCEA Kinase
Transketolase
Aldolase
cFBP aldolase
Rubisco
FBP aldolase
FBPase
SBPase
PRK
ADPGPP
PGCAPase
GOA Oxidase
GGAT
GDC
cFBPase
F26BPase
GSAT
SPS
UDPGP
SPP
GAPDH
Zhu et al (2007) Plant Physiology
13
Theoretical optimal concentrations of enzymes in
carbon metabolism
Zhu et al (2007) Plant Physiology
14
Raines (2003) Photosynthesis Research
15
Zhu et al (2004) Plant Cell Environ
16
Steady State Photosynthesis Model
CO2 H2O Light Energy ? ? CH2O O2
Light
Farquhar et al (1980) Planta
17
Zhu et al (2004) Plant Cell Environ
18
(No Transcript)
19
 
 
Zhu et al (2004) Plant Cell Environ Long et al
(2006) Plant Cell Environ
20
New Pathways Design
Kebeish et al 2007 Nature
21
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
22
Maintaining Efficiency

• Photo-protection
• Temperature Stresses
• Water stress

23
Photoprotective state changes light response curve
Asat
?
Non-Photoprotective
CO2 uptake
Photoprotective
?
Light Level
24
Asat
?
CO2 uptake
?
High Light
Low Light
Light
25
12 ?
0.2 ?
26
Case 2
Case 1
The Reverse Ray Tracing Algorithm
Zhu et al (2004) J. Exp. Botany
27
Zhu et al (2004) J. Exp. Botany
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Zhu et al (2004) J. Exp. Botany
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Options to engineer higher photosynthetic energy
conversion efficiency (ec)
Alteration increase in ec Speculated Time Horizon (yr) Ref
Improved canopy architecture 10 (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 photosynthesis 15 (6-40) 5 Zhu et al (2004 a)
Introduction of higher catalytic rate foreign forms of Rubisco 22 (17-30) 5-10 Zhu et al (2004 b)
Altered allocation of resources within photosynthetic apparatus 30 (0-60) 0-5 Zhu et al (2007)
Efficient C4 photosynthesis engineered into C3 crops 30 15-30 Zhu et al (2008)
30
Why hasnt evolution already maximized
photosynthetic production ?
31
Wild plants versus designed crops (1)
The Calvin Cycle
Photo-respiratory pathway
Photo-respiratory pathway
The Calvin Cycle
Designed final leaf
Beginning leaf
25 oC Well watered
32
Wild plants versus designed crops (2)
The Calvin Cycle
Photo-respiratory pathway
Photo-respiratory pathway
The Calvin Cycle
Designed final leaf
Beginning leaf
45 oC Drought
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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
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Systems Biology and Synthetic Biology
Systems Biology Resource use efficiency,
optimality, plasticity, environmental
stochasticity and heterogeneity, genetic
constraints
Mathematical Models Evolutionary algorithms
Synthetic Biology New pathway design, new
genetic regulatory network design , redesign
existing parts, devices, systems etc
35
Conclusions

• There 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.

36
ACKNOWLEDGEMENTS

• Collaborators
• Prof. 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)

• PICB
• Vincent Devloo
• Danny Tholen
• GuiLian Zhang
• FuQiao Xu
• LinYing Lu
• Caroline Tholen
• ChangPeng Xin
• YuJing Sun
• Xin Yan
• Li Kai
• Chang Xiao
• HongBo Lei
• Roman
• SU