Translational Dynamics of Leaf and Chloroplast Development in Maize

PI: Alice Barkan (University of Oregon)CoPI: Thomas P. Brutnell （Donald Danforth Plant Science Center）该项目将利用遗传学和基因组学的方法，通过探索C4植物中受调节的翻译如何促进二态叶绿体的分化，以及在影响光合效率的变化光条件下维持光合稳态，来发展“从基因组到系统水平的植物与环境相互作用的理解”。对C4作物玉米的关注尤其相关，因为C4光合作用可能进化为减少光呼吸，从而使植物更有效地利用氮和水。因此，更深入地了解驱动C4分化的调控网络将有助于增强原生C4植物和将C4性状工程转化为C3作物。在外联和培训方面，该项目将为高中生、本科生和研究生提供教育机会。俄勒冈大学本科生的实验课程将与叶绿体生物发生中潜在缺陷的大规模突变鉴定相结合。圣路易斯的一个项目将让中学生亲自动手分析谷子的光合作用突变体。本科生，研究生和博士后学生将获得指导的研究经验，涉及尖端的遗传，基因组和分子方法。最后，该项目将为更广泛的植物基因组研究界开发工具和资源，包括(1)~6000个新的序列索引的Mu插入，可以通过MaizeGDB和内部搜索界面（http://teosinte.uoregon.edu/mu-illumina/）访问；(2)为假定的mu标记等位基因提供基因鉴定服务；(3)约100个玉米光合作用必需基因的功能注释和相关突变库；(4)通过社区浏览器提供改进的基因组注释；(5)用于阐明共表达模块和相关功能推断的大规模翻译组和转录组数据集。叶绿体是植物中的亚细胞细胞器，它容纳光合作用和许多其他基本代谢过程的机器。叶绿体在不同的细胞类型中具有不同的形态和功能，如C4植物的束鞘和叶肉细胞中的二态叶绿体。它们是动态的细胞器，能够快速适应外部环境的变化，从而优化光合作用性能，同时最大限度地减少光氧化损伤。该项目将通过采用最先进的方法和广泛收集的非光合突变体来阐明叶绿体的生物发生、分化和环境适应。之所以选择玉米作为实验生物，是因为玉米是一种具有二态叶绿体的C4植物，它提供了丰富的叶绿体生物发生突变体，并且玉米叶片是描述分生组织细胞向光合能力叶片细胞分化的发育过程的一个很好的实验系统。该项目的具体目标是：(1)使用大规模的前向遗传策略，为玉米光合作用所需的约100个基因分配分子和生理功能；(2)使用最先进的核糖体分析策略来定义光合装置和束鞘和叶肉细胞中不同蛋白质组的安装背后的翻译体动力学；(3)全面描述光合叶片组织分化过程中线粒体和质体基因表达的进展；(4)发现细胞质和叶绿体中受调控的翻译如何在光照变化条件下维持光合稳态。

PI: Alice Barkan (University of Oregon)CoPI: Thomas P. Brutnell (Donald Danforth Plant Science Center)This project will use genetic and genomic approaches to develop "a genome to systems-level understanding of plant-environmental interactions" by exploring how regulated translation contributes to the differentiation of the dimorphic chloroplasts in C4 plants and to maintaining photosynthetic homeostasis under shifting light conditions that compromise photosynthetic efficiency. The focus on maize, a C4 crop plant, is especially pertinent, as C4 photosynthesis likely evolved to reduce photorespiration, resulting in plants that use nitrogen and water more efficiently. Thus a deeper understanding of the regulatory networks driving C4 differentiation will aid in the enhancement of native C4 plants and in engineering C4 traits into C3 crops. With regard to outreach and training, the project will offer educational opportunities for high school, undergraduate and postgraduate students. A laboratory course for University of Oregon undergraduates will be integrated with the large-scale identification of mutations underlying defects in chloroplast biogenesis. A program in St. Louis will engage secondary school students in hands-on analysis of photosynthetic mutants in foxtail millet. Undergraduate, graduate, and postdoctoral students will gain mentored research experience involving cutting-edge genetic, genomic, and molecular approaches. Finally, the project will develop tools and resources for the broader plant genomics research community that include (1) ~6000 new sequence-indexed Mu insertions which can be accessed via MaizeGDB and an in-house search interface (http://teosinte.uoregon.edu/mu-illumina/); (2) a gene identification service for putative Mu-tagged alleles; (3) functional annotations and associated mutant stocks for ~100 maize genes that are essential for photosynthesis; (4) improved genome annotations to be made available through community browsers; and (5) large-scale translatome and transcriptome datasets for the elucidation of coexpression modules and associated functional inferences. Chloroplasts are subcellular organelles in plants that house the machinery for photosynthesis and numerous other essential metabolic processes. Chloroplasts acquire different forms and functions in different cell types, as exemplified by the dimorphic chloroplasts in the bundle sheath and mesophyll cells of C4 plants. They are dynamic organelles that adapt rapidly to changes in the external environment in a manner that optimizes photosynthetic performance while minimizing photo-oxidative damage. This project will elucidate the biogenesis, differentiation, and environmental adaptation of chloroplasts by employing state-of-the-art methods and an extensive collection of non-photosynthetic mutants. Maize is chosen as the experimental organism because it is a C4 plant with dimorphic chloroplasts, it offers a rich collection of chloroplast biogenesis mutants, and the maize leaf blade is an excellent experimental system for describing the developmental progression through which meristematic cells differentiate into photosynthetically-competent leaf cells. The specific objectives of the project are to (1) use a large-scale forward genetic strategy to assign molecular and physiological functions to ~100 genes in maize that are required for photosynthesis; (2) use a state-of-the-art ribosome profiling strategy to define the translatome dynamics underlying the installation of the photosynthetic apparatus and the distinct proteomes in bundle sheath and mesophyll cells; (3) provide a comprehensive description of the progression of mitochondrial and plastid gene expression during the differentiation of photosynthetic leaf tissue; and (4) discover how regulated translation in the cytosol and chloroplast contribute to maintaining photosynthetic homeostasis under shifting light conditions.