Improvement of photosynthesis by modification of light harvesting systems

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Photosynthetic organisms can proceed photosynthesis under various light conditions on the Earth. Plants employ two strategies to adapt light intensities, one is the dissipation of excess light energy as heat and the other mechanism is the regulation of light harvesting apparatus. Capturing light energy is the first step of photosynthesis and the regulation of the amount of harvesting light energy directly influences the rate of photosynthesis. There are many reports on the employment of genetic engineering for the improvement of agricultural production . Most typical successes were to improve the resistances to virus infection and insect attack. However, these genetic engineerings do not increase productivity itself. In order to increase the productivity of the plants, the ability of photosynthesis must be modified. The aims of this project are 1) to clarify the mechanisms of the acclimation of antenna size to light intensities, 2) modification of antenna size to improve productivities. Green plants have large antenna size under low light conditions in order to capture light energy for photosynthesis. In this case, the level of CAO mRNA was high and chlorophyll b was actively synthesized. However, in CAO over expressed lines of Arabidopsis thaliana, the level of CAO mRNA and the antenna size was almost same under wide range of light intensities. We concluded from the above experiments that CAO plays a central role in regulating the antenna size under various light intensities. We also found CAO over-expressed mutants grow well under low light intensities compared to wild type. It indicates that modifications of photosynthesis are potentially powerful tool to increase the productivities of the plants.