Improvement of photosynthesis by modification of light harvesting systems

地球上的光合作用生物可以在各种光照条件下进行光合作用。植物采用两种策略来适应光强，一种是将多余的光能转化为热量，另一种机制是对光收集装置的调节。捕获光能是光合作用的第一步，对光能捕获量的调节直接影响光合作用的速率。关于利用基因工程改善农业生产的报道很多。最典型的成功是提高了对病毒感染和虫害的抵抗力。然而，这些基因工程本身并不能提高生产率。为了提高植物的生产力，必须改变植物的光合作用能力。该项目的目的是1)阐明天线尺寸适应光强的机制，2)修改天线尺寸以提高生产率。绿色植物在弱光条件下有较大的天线尺寸，以捕捉光合作用所需的光能。在这种情况下，CAO mRNA水平较高，叶绿素b合成活跃。然而，在CAO过表达的拟南芥品系中，在较宽的光照强度下，CAO基因的表达水平和天线大小几乎相同。通过以上实验，我们得出结论：在不同的光强下，CAO在调节天线尺寸方面起着核心作用。我们还发现，与野生型相比，CAO过表达的突变体在弱光下生长得更好。这表明，光合作用的调节是提高植物生产力的潜在的有力工具。

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.