The well-known phenomenon of "everything grows by the sun" is based on the principle of oxygen-type photosynthesis in organisms such as higher plants, algae and cyanobacteria. These organisms fix CO2 by photosynthesis, convert solar energy into chemical energy and store it, while cleaving water molecules and releasing oxygen for biological respiration. Photosynthesis is the most important biochemical reaction on Earth, providing the material basis for the life of the Earth's creatures. Therefore, improving the photosynthesis efficiency is of great significance for the effective use of solar energy, promotion of agricultural production and income increase, acceleration of industrial CO2 emission reduction and resource utilization.
Photosynthesis is an extremely complex biochemical process. According to the need for light, photosynthesis is artificially divided into light and dark reactions. In the past, the research on the transformation of photosynthesis mainly focused on how to improve the utilization and conversion efficiency of light energy by light reaction or enhance the carbon capture efficiency of Rubisco, a key enzyme in the dark reaction, and seldom consider how to improve the coupling efficiency of light reaction and dark reaction. In the actual physiological process, photosynthesis light reaction and dark reaction are inseparable organic whole. Photoreaction generates energy (ATP) and reducing power (NADPH), while dark reactions require the depletion of ATP and NADPH to achieve reductive fixation of CO2.
According to the basic principle of ATP and NADPH coupling in light reaction, the ATP generated by photoreaction can not meet the energy requirement of dark reaction and carbon fixation. Based on the overall situation of cells, photosynthesis Photoperiod and dark reaction as the organic whole, taking the NADPH linking photosynthetic photoreaction and dark reaction as the starting point, a new coupling module of introducing NADPH depletion module was put forward to break the cell's inherent NADPH balance, and the effective coupling between photoreaction and dark reaction The new concept of enhancing the intrinsic driving force of photoreactions and thus the efficiency of photosynthesis.
Using photosynthetic-oxygen-bacteria cyanobacteria as a research model, the researchers created an isopropanol biosynthetic pathway that consumes only NADPH without extra ATP by introducing an NADPH-dependent dehydrogenase (see photo). A series of photosynthetic physiological and biochemical analysis showed that the introduction of NADPH depletion pathway, cell growth was significantly accelerated, photosynthesis efficiency increased by about 50%, at the same time with higher cell activity. At the same time, it was found that the light saturation point of cyanobacteria doubled after transformation, indicating that it can tolerate higher light intensity, which is of great significance to adapt to the dramatic changes of light intensity in nature. This result shows that the reduction-driven global cell metabolism strategy can improve the photosynthesis efficiency more effectively than the traditional single-modification photoreaction or dark-reaction, which is of great value to the transformation of photosynthesis in eukaryotes.
The work was published online August 4 in Metabolic Engineering magazine. The research was funded by the National Natural Science Foundation of China and the key project of Chinese Academy of Sciences entitled "Artificial Bioconversion of Carbon Dioxide". Associate researcher Zhou Jie and doctoral student Zhang Fuliang are co-authors of the dissertation.
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