Single Cell C4 Photosynthesis: Control of Cell Organization and Function

绿色植物，因此，最终，所有其他更高级的生命形式，依赖于被称为光合作用的光驱动过程中从二氧化碳中提取的有机碳。大多数植物通过Rubisco酶直接固定二氧化碳，生成一种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，这是一个相反的生产过程。一些陆生植物通过4碳途径进化出一种二氧化碳浓缩机制(CCM)，即C4植物，它增加Rubisco部位的CO2水平，抑制加氧酶活性。Kranz解剖学被认为是具有C4光合作用的陆地植物的一个范例和主要特征，它由两种在生物化学和解剖学上不同的协同作用的光合作用细胞类型组成。已经建立了一种教条，即C4光合作用的运作需要Kranz解剖学。现在发现两个不同的物种，Borszczowia aralocaspica和Bienertia Cycloptera，在一个光合作用细胞中进行C4光合作用，即没有Kranz解剖结构，这打破了这种范式。这些物种通过细胞器和光合酶的空间分隔，展示了单个细胞内C4机制功能的独立的、新颖的解决方案。研究这些细胞的学术价值在于，它们提供了最精致的模型系统，用于探索单个细胞中复杂的结构和功能极性的调节，并将在我们对细胞组织和光合碳同化的理解方面开辟新的天地。这项拟议的工作将描述使在单个细胞中实现C4光合作用成为可能的机制，直到最近发现这两个物种之前，这被认为是不可能在陆地植物中实现的。将结合细胞生物学、生化和分子技术来探索单细胞C4综合征的发展基础，以及使这一点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的更好的理解和新的模型。拟议的工作还将使我们对可操作的C4光合作用机制的要求有新的见解。这些信息对于设计将C4型碳固定转化为C3作物物种的策略将是重要的，这有可能提高作物生产力。此外，这些研究将迫使重新评估C4综合征在植物中的进化。

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.