Single Cell C4 Photosynthesis: Control of Cell Organization and Function

绿色植物，最终，所有其他高级生命形式，都依赖于由二氧化碳产生的有机碳，这一过程被称为光合作用。大多数植物通过Rubisco酶直接固定二氧化碳，产生3碳化合物，被称为C3植物。由于Rubisco的加氧酶活性，C3植物表现出高速率的光呼吸，这是一个反生产过程。一些陆生植物通过4碳途径进化出了CO2浓缩机制；因此被称为C4植物，它增加了Rubisco位点的二氧化碳水平，抑制了加氧酶的活性。克兰兹解剖结构被认为是陆地植物C4光合作用的一个范例和主要特征，它由两种生物化学和解剖学上不同的光合细胞类型组成，它们协调作用。一个教条已经确立，克兰兹解剖结构是C4光合作用的操作所必需的。这种模式现在已经被两个不同的物种打破了，Borszczowia aralocaspica和Bienertia cycloptera，它们在一个光合细胞中进行C4光合作用，也就是说，没有克兰兹解剖结构。这些物种通过细胞器和光合酶的空间分隔，在单个细胞内表现出独立的、新颖的C4机制功能解决方案。研究这些细胞的智力价值在于，它们提供了最精致的模型系统，用于探索单个细胞中复杂结构和功能极性的调节，并将在我们对细胞组织和光合作用碳同化的理解方面开辟新天地。这项提议的工作将描述在单个细胞中实现C4光合作用的机制，直到最近这两个物种的发现才被认为是不可能在陆生植物中实现的。细胞生物学、生物化学和分子技术的结合将被用来探索单细胞C4综合征发展的基础和使之成为可能的细胞组织参数。所获得的信息将导致对植物细胞组织和生化极性的产生有更深入的了解，并建立新的模型。拟议的工作也将使我们对可操作的C4光合作用机制的要求有新的认识。这些信息对于设计C3作物的c4型固碳工程策略具有重要意义，具有提高作物生产力的潜力。此外，这些研究将迫使对植物C4综合征进化的重新评估。

Green plants, and therefore, ultimately, all other higher forms of life, depend on organic carbon derived from CO2 by a light driven process referred to as photosynthesis. Most plants fix CO2 directly by the enzyme Rubisco, generating a 3 carbon compound, and are called C3 plants. C3 plants show high rates of photorespiration, a counter-productive process, due to the oxygenase activity of Rubisco. Some terrestrial plants have evolved a CO2 concentrating mechanism (CCM) through a 4 carbon pathway; thus called C4 plants, which increases the level of CO2 at the site of Rubisco, depressing the oxygenase activity. Kranz anatomy became recognized as a paradigm and major distinguishing feature of terrestrial plants with C4 photosynthesis, and consists of two biochemically and anatomically distinct photosynthetic cell types that act coordinately. A dogma has been established that Kranz anatomy is required for the operation of C4 photosynthesis. This paradigm has now been broken with the discovery that two different species, Borszczowia aralocaspica and Bienertia cycloptera, that perform C4 photosynthesis in a single photosynthetic cell, i.e. without Kranz anatomy. These species exhibit independent, novel solutions for the function of the C4 mechanism within a single cell through spatial compartmentation of organelles and photosynthetic enzymes. The intellectual merit of studying these cells is that they provide the most exquisite model systems with which to probe regulation of complex structural and functional polarity in a single cell and will break new ground in our understanding of cellular organization and photosynthetic carbon assimilation. The proposed work will characterize the mechanisms that make it possible to achieve C4 photosynthesis in a single cell, which until the recent discovery of these two species was thought to be impossible in terrestrial plants. A combination of cell biology, biochemical and molecular techniques will be employed to probe the foundations of development of the single-celled C4 syndrome and the parameters of cellular organization that make this possible. The information gained will lead to a greater understanding, and new models, of generation of plant cellular organization and biochemical polarity. The proposed work will also give us new insight into requirements for an operational C4 photosynthetic mechanism. This information will be important to designing strategies to engineer C4-type carbon fixation into C3 crop species, which has the potential to increase crop productivity. In addition, these studies will force a re-evaluation of evolution of the C4 syndrome in plants.