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