Untitled - 中国植物生理与分子生物学学会

triose phosphate utilization (Zhu et al 2007). After these validations, the photosynthetic carbon
metabolism model can be used to identify new targets to engineer higher photosynthetic efficiency.
II) Combining systems model with evolutionary algorithm to identify new targets to engineer for
higher productivity
The evolutionary algorithm essentially mimics the process of natural selection. In real natural
selection, the selection pressure is to ensure survival and higher fecundity. In the artificial selection
mimicked by the evolutionary algorithm, the selection pressure is to gain a higher photosynthetic
CO 2 uptake rate with the same amount of nitrogen investment in the enzymes in the photosynthetic
carbon metabolism. Furthermore, each generation has many individuals, with each individual
representing one set of enzyme concentrations required to run the model of the Carbon metabolism.
For each individual, or set of enzyme concentrations, there is one steady-state rate of CO 2 uptake
rate. In each generation, the individual with the highest photosynthetic CO 2 uptake rate will be
selected to “seed” the next generation. To generate individuals for the next generations, the selected
individual will be duplicated to generate a population, then the individuals in this populated will be
“mutated” (i.e. adding random variations to the enzyme concentrations). This process of selection
and mutation iterates and the rate of photosynthetic CO 2 uptake rate gradually increases over
generations. This process terminates when the rate of photosynthesis cannot be increased with more
generations (Zhu et al 2007). The final nitrogen distribution in the enzyme set is considered as the
optimal nitrogen distribution.Using this approach, we showed that RuBisco,
Sedoheptulose-l,7-bisphosphatase (SBPase) and Fructose-2,6-bisphosphatase (FBPase) need to be
increased for a higher photosynthetic CO 2 uptake rate. Furthermore, the increase in sink capacity
(through increase in ADP glucose pyrophosphorylase, one key enzyme in starch synthesis) is also
predicted to increase photosynthetic capacity. The nitrogen required to increase activities of these
enzymes are predicted to be reallocated from photorespiratory pathway (Zhu et al 2007). SBPase,
one of the enzymes identified to be increased to gain higher photosynthesis, has been
over-expressed in tobacco, which led to higher photosynthesis and biomass production (Lefebvre et
al 2005), demonstrating that combining evolutionary algorithm with systems models can identify
potential engineering targets for higher photosynthesis.
Other major applications of photosynthesis systems models
Dynamic systems models hold a variety of other applications. First, systems models provide a
direct link between genomic data and phenotypic data. Second, systems model can be used to study
the adaptive significance of molecular changes in photosynthetic apparatus to photosynthetic
efficiency. Thirdly, dynamic systems models can be used to test hypotheses regarding mechanisms
underlying dynamic changes in photosynthesis. Fourthly, systems model of photosynthesis can be
used in eco-physiological crop simulation models to enable direct linkage fro genome to ecosystem.
Literature
Zhu X-G, de Sturler E, Long SP (2007) Plant Physiology 145: 513-526
Lefebvre S et al (2005) Plant Physiology 138: 451-460
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