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

植物和藻类等光合作用生物执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有机产品，对所有形式的生命的生长和发展至关重要。在陆地植物中，C3、C4和景天酸代谢(CAM)三种光合作用模式已被确定，其中C4和CAM植物在二氧化碳限制条件下效率最高。四十多年来，人们普遍认为，C4光合作用需要两种类型的细胞相互作用，即Kranz解剖学，每种细胞都有不同的叶绿体超微结构和生化。这种Kranz范式最近受到挑战，发现藜科的四个成员在单个细胞内执行C4光合作用途径。这些鸟脚类物种通过将主要细胞器和关键的光合酶划分为两个独立的胞内细胞质亚室，实现了在单个细胞中进行C4光合作用的新方法。因此，这些独特的物种提供了理想的模式系统，用来研究控制单个植物细胞中复杂结构和功能极性发展的调控因素。 我的研究计划的长期目标是阐明单细胞C4光合作用的发育和功能的细胞和分子机制。这将通过结合生化、生物信息学、细胞、分子遗传学和生理学技术的各种方法来解决。我们有证据表明，这些光合作用基因的表达在转录后水平上受到调节，并已开发出分子工具来表征这些机制。因此，我的短期目标是：(1)描述在单细胞C4系统建立过程中调节光合作用基因表达的分子过程；(2)描述蛋白质输入途径，该途径负责选择性地将蛋白质输入到二态叶绿体中，使C4途径在单细胞中发挥作用；(3)研究细胞骨架及其相互作用的蛋白质在细胞器运动中的作用，从而在单细胞C4系统和CAM系统中建立细胞极性。了解这一复杂而有趣的光合作用途径的分子基础将有助于深入了解这些植物如何在高温和水分胁迫条件下茁壮成长，这可能严重影响更常见和较不专门的C3植物的光合作用生产力。在当前全球不稳定的天气模式下，这一点可能很重要，因为更高的温度导致二氧化碳可获得性减少和水分压力增加，这将为具有C4特征的植物提供优势。

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.