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Organic substances which serve as a source of food and fossil fuel are formed by photosynthesis in plants. We are conducting research aimed at alleviating the two major factors restricting the photosynthesis by plants to elevate the productivity of photosynthesis (Fig. 1). One of these two factors is RuBisCO, which is the most important enzyme involved in photosynthesis and catalyzes the formation of organic substances from CO2. The rate of the reaction catalyzed by RuBisCO is quite low, and the capability of this enzyme to recognize CO2 is low, thus reducing the overall efficiency of photosynthesis. The second factor is stress due to strong light and dryness, affecting the plants seriously. If the stomata of the plant is closed due to dryness, photosynthesis does not occur. Excessive light energy can produce oxygen radicals, injuring the plant cells and eventually leading to injuring of the plant. If plants with high performance RuBisCO and resistance to stress (due to strong light and dryness) can be developed, they will remarkably increase the production of food and other resources and will also contribute to covering the deserts (currently seen in many areas on the globe) with trees.
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- Modification of plant RuBisCO (Fig. 2)
We have discovered a super RuBisCO that is relatively specialized for CO2 fixation in red algae and a living fossil gene for RuBisCO-related proteins in Bacillus. We are interested in the molecular mechanism of the evolution of the ancestral gene to a wide variety of RuBisCOs with diverse affinities for CO2, together with the development of the Calvin cycle. Information from these researches related to the structure-function relationship of RuBisCO and its related proteins will provide us with a great deal of ideas in improving the enzymatic properties of RuBisCO. RuBisCO is synthesized and accumulated in a high concentration for photosynthetic CO2 fixation in chloroplasts with aid of various chaperons. Genetic analysis of these chaperons are also under way.
- Analysis of the mechanism of wild watermelon for resistance to dryness and strong light (Fig. 3)
We are analyzing the mechanism for resistance to dryness and strong light, using wild type watermelon (C3 plant growing naturally in the Kalahari Desert) as a model. Stress-related genes are surveyed exhaustively by proteomics and transcriptomics. Furthermore, we are analyzing the function and mechanism of metabolism of citrullin (a new compatible solute which scavenges hydroxyl radical, the most toxic active oxygen), and exploring a new mechanism for dissipating excessive light energy. We attempt to express key genes in C3 crop plants to make the plants resistant to dryness and strong light.
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- Takahara K. et al., FebsJ., 272, 5353-5364, 2005
- Munekage Y. et al., Plant Biotech., 22, 361-369 2005
- Nanasato Y. et al., Plant Cell Physiol., 46, 1515-24 2005
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- Akashi K. et al., Plant Biotech., 22, 13-18 2005
- Akashi K. et al., Biochem Biophys Res Commun., 323, 72-78, 2004
- Ashida H. et al., Science, 302, 286-290, 2003
- Mizohata E. et al., Biochem Biophys Res Commun., 301, 591-8 2003
- Nakahara K. et al., Plant Cell Physiol., 44, 326-333, 2003
- Yokota A. et al., Ann Bot., 89, 825-32 2002
- Akashi K. et al., FEBS Lett., 508, 438-42 2001
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Fig. 1 Approach to modification of plant function
Fig. 2 Research for creation of super-RuBisCO
Fig. 3 Analysis of the mechanism for resistance of wild type watermelon to strong light and dryness
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