Cellular and molecular mechanisms underlying single-cell C4 photosynthesis in Chenopodiaceae species

植物和光合生物（如藻类）进行最重要的生物过程，即光合作用，将大气中的二氧化碳转化为所有生命形式生长和发育所必需的有机产物。在陆生植物中，已经确定了C3、C4和天冬酸代谢（CAM）三种光合作用模式，其中C4和CAM植物在CO2限制条件下效率最高。四十多年来，人们普遍认为C4光合作用需要两种被称为克兰兹解剖的细胞类型的相互作用，每种细胞类型具有不同的叶绿体超微结构和生物化学。这一Kranz范式最近受到了挑战，发现Chenopodiaceae家族的四个成员在单个细胞内进行C4光合作用途径。这些藜足类动物通过将主要细胞器和关键光合酶分配到两个独立的胞质亚室，实现了在单个细胞内进行C4光合作用的新手段。因此，这些独特的物种提供了理想的模型系统，用于研究控制单个植物细胞中复杂结构和功能极性发育的调节因子。

Plants and photosynthetic organisms such as algae perform the most important biological process known as photosynthesis that converts atmospheric CO2 into organic products essential for growth and development of all forms of life. In terrestrial plants, three modes of photosynthesis, C3, C4 and Crassulacean acid metabolism (CAM), have been identified with C4 and CAM plants being the most efficient under CO2 limiting conditions. For more than forty years, it has been widely accepted that the C4 photosynthesis requires the interaction of two cell types known as Kranz anatomy, each has distinct chloroplast ultrastructure and biochemistry. This Kranz paradigm was recently challenged with findings that four members of family Chenopodiaceae perform C4 photosynthetic pathway within individual cells. These chenopod species achieve novel means for performing the C4 photosynthesis in a single cell by partitioning of major organelles and key photosynthetic enzymes into two separate intracellular cytoplasmic subcompartments. Thus, these unique species provide ideal model systems with which to examine the regulatory factors controlling the development of complex structural and functional polarity in a single plant cell. The long-term goal of my research program is to elucidate the cellular and molecular mechanisms responsible for the development and function of single-cell C4 photosynthesis. This will be addressed through various approaches that combine biochemical, bioinformatics, cellular, molecular genetics, and physiological techniques. We have evidence that the expression of these photosynthetic genes is regulated at a posttranscriptional level and have developed molecular tools to characterize these mechanisms. Thus, my short-term objectives are to: (1) characterize the molecular processes that regulate the expression of photosynthetic genes during the establishment of the single-cell C4 system (2) characterize the protein import pathway responsible for the selective import of proteins into the dimorphic chloroplasts allowing the C4 pathway to function in a single cell, (3) examine the role of the cytoskeleton and its interacting proteins involved in the movement of organelles leading to the establishment of cellular polarity in the single-cell C4 systems and CAM systems. Understanding the molecular basis of this complex and interesting photosynthetic pathway will provide insights into how these plants thrive under conditions of high temperature and water stress which can severely affect photosynthetic productivity in the more common and less specialized C3 plants. This could be important under the current global unstable weather patterns, where reduced CO2 availability and increased water stress caused by higher temperatures would offer an advantage to plants with C4 features.