IOS: The Link between Chloroplast Metabolism and Plasmodesmata-mediated Carbon Partitioning

光合作用的最终产物蔗糖从叶子输出到植物的其余部分，在那里它被用作新陈代谢的能量来源。蔗糖的这种分布对于植物生长和发育是必不可少的。蔗糖在细胞之间通过的主要途径是通过称为胞间连丝（PD）的细胞质通道。虽然PD长期以来一直被认为是存在的，并对蔗糖转运的重要性，我们仍然不知道PD的发展和功能是如何调节。有越来越多的证据表明，叶绿体，植物细胞器进行光合作用，产生蔗糖，产生信号，可以调节PD。本项目将确定叶绿体功能如何影响PD调节蔗糖运输。这项研究的结果将引起植物生物学家的广泛兴趣，从长远来看，也应该为基因工程提供新的目标，努力开发具有微调控制碳分配的植物。这可能会产生具有更好的碳分配模式的植物，以满足人类对作物生产的需求。一些高中和本科生将参与这个项目，并将获得实践经验，在进行研究。这将有助于NSF实现其整合研究和教育的目标。植物体内的碳分配取决于碳固定与运输的协调。胞间连丝（PD）允许糖进出植物脉管系统，以便重新分配到需要光合同化物的组织。人们早就知道植物生理学显著影响PD和细胞间运输，但这是如何实现的仍不清楚。 在以前的工作与ise 2突变体的基础上，提出叶绿体调节光合作用和PD之间的平衡。ISE 2是一个进化上保守的核基因，编码叶绿体RNA解旋酶。本研究的目的是描述这种叶绿体RNA解旋酶在叶绿体中的功能，并阐明其对PD的影响。 该项目的具体目标是：1）阐明ISE 2在叶绿体中的分子功能，2）了解叶绿体光合输出如何改变PD形成和细胞间运输，3）表征其他叶绿体突变体的PD结构和运输特性。本提案中提出的问题影响了植物细胞生物学的两个重要领域。第一个是长期存在的问题，即如何通过PD调节细胞间的碳通量。其次是叶绿体中的RNA加工，这是一个有趣的过程，代表了核和细胞器基因组之间基因表达协调的关键步骤，为细胞器从其原核起源作为内共生体的进化提供了见解。生物化学和分子生物学方法的组合将用于调查ISE 2的分子功能;细胞间运输将通过使用荧光分子进行监测;和PD将通过透射电子显微镜和共聚焦荧光显微镜可视化。深入了解叶绿体和PD之间的关系将增加我们对植物如何将局部生理和环境线索整合到具有系统影响的决策中的理解。该提案中的研究对细胞间运输进行了全面的研究，所产生的结果可能会将PD作为碳通量的被动介质的范式转变为PD，作为将局部细胞生理学与整个生物体反应相结合的更大战略的一部分。

The end product of photosynthesis, sucrose, is exported from leaves to the rest of the plant where it is used as an energy source for metabolism. This distribution of sucrose is essential for plant growth and development. A major route for passage of sucrose between cells is via cytoplasmic channels called plasmodesmata (PD). Although PD have long been known to exist and to be important for sucrose transport, we still do not know how PD development and function are regulated. There is accumulating evidence that chloroplasts, the plant organelles that perform photosynthesis to generate sucrose, produce signals that can regulate PD. This project will determine how chloroplast function impacts PD to regulate sucrose transport. The results of this research will be of broad interest to plant biologists, and in the long term should also provide novel targets for genetic engineering in efforts to develop plants with fine-tuned control of carbon partitioning. This may produce plants with better carbon allocation patterns to meet increased human demands for crop production. Several high school and undergraduate students will be involved in this project, and will gain hands-on experience in conducting research. This will help the NSF meet its goal of integrating research and education. Carbon partitioning in plants depends on the coordination of carbon fixation with transport. Plasmodesmata (PD) allow the passage of sugars to and from the plant vasculature for redistribution to tissues that require photoassimilates. It has long been known that plant physiology significantly impacts PD and intercellular trafficking, but how this is accomplished remains unclear. On the basis of previous work with the ise2 mutant, it is proposed that chloroplasts regulate the balance between photosynthesis and PD. ISE2 is an evolutionarily conserved nuclear gene that encodes a chloroplast RNA helicase. The objective of this study is to characterize the function of this chloroplast RNA helicase in chloroplasts and to elucidate its impacts on PD. Specific goals of this project are to: 1) elucidate the molecular function of ISE2 in the chloroplast, 2) understand how chloroplast photosynthetic output alters PD formation and intercellular trafficking, and 3) characterize other chloroplast mutants with altered PD structure and trafficking properties. The questions addressed in this proposal impact two important areas of plant cell biology. The first is the longstanding question of how intercellular flux of carbon via PD is regulated. Second is RNA processing in the chloroplast, an intriguing process that represents a crucial step in the coordination of gene expression between nuclear and organellar genomes, providing insight into the evolution of the organelle from its prokaryotic origins as an endosymbiont. A combination of biochemical and molecular biological approaches will be used to investigate ISE2's molecular function; intercellular trafficking will be monitored through the use of fluorescent molecules; and PD will be visualized by transmission electron microscopy and confocal fluorescence microscopy. Insight into the relationship between chloroplasts and PD will increase our understanding of how plants integrate local physiological and environmental cues into decisions that have systemic implications. The research in this proposal takes a holistic view of intercellular trafficking, and the results generated could potentially shift the paradigm from PD as passive mediators of carbon flux to PD as part of a larger strategy for integrating local, cellular physiology with whole organism responses.