Evolutionary Assembly of C4 Leaf Structure

C4叶结构的进化组装

• 批准号: RGPIN-2020-05925
• 负责人: Sage, Tammy
• 金额: $ 2.91万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751456
• 关键词: Evolutionary; Assembly; C4; Leaf; Structure

Ribulose bisphosphate carboxylase-oxygenase (Rubisco), is the primary autotrophic carboxylase in oxygenic photosynthetic organisms. Oxygenase activity of Rubisco results in production of cytotoxic phosphoglycolate that is removed by photorespiration. Photorespiration releases previously fixed CO2 resulting in a net loss of carbon for growth. C4 photosynthesis concentrates CO2 around Rubisco relative to O2 eliminating Rubisco oxygenase activity. An essential feature of the C4 carbon concentrating mechanism is the spatial separation of the initial fixation of CO2 by phosphoenolpyruvate carboxylase in mesopyhyll cells from secondary refixation of CO2 by Rubisco in bundle sheath (BS) cells surrounding vascular tissue. Initial fixation produces a C4-acid that is transported to BS cells where it is decarboxylated enhancing CO2 around Rubisco 15-fold. The purpose of this research is to test our hypothesis that evolution of C4 photosynthetic leaf structure from C3 photosynthetic ancestors arises from cis- and trans-regulatory divergence of genes involved in tissue patterning, cell and plastid division/expansion, plasmodesmata and VT formation, and auxin biosynthesis, signalling and transport. We will determine the spatial-temporal series of events giving rise to the cellular/tissue architecture of a C4 photosynthetic leaf that is essential for photosynthetic function. Comparative studies on leaf development in Atriplex prostrata (C3), A. rosea (C4) and their C3xC4 F1 hybrid will be conducted and analyzed in the context of RNA-seq/genomic data already obtained by our laboratory. We will confirm 3-D patterns of cell division/expansion, as well as chloroplast/plasmodesmata development in M and BS cells. These features will be obtained using confocal microscopy, serial block-face scanning electron microscopy, high resolution transmission electron microscopy of thin sections and immunodetection of proteins and localization of the reactive oxygen species H2O2 with transmission electron microscopy.  Immunohistochemistry will be performed using antibodies to detect auxin and proteins involved in tissue patterning, cell and plastid division/expansion, and plasmodesmata formation. C4 photosynthesis has evolved independently over 60 times making it one of the best examples of evolutionary convergence in the living world. C4 photosynthesis accounts for 23% of terrestrial gross primary productivity although it only occurs in 3% of plant species. In spite of the importance of C4 photosynthesis, our understanding of the cellular and molecular control of C4 evolution is in its infancy. Results from our study will enable identification of key genes essential for C4 leaf structure/function and regulation of those genes. To maintain global food security, cereal production will have to increase 70% by 2050. Our study will provide information to assist in maintaining global food security by engineering the C4 pathway into C3 crops, as is now being done in rice.

核酮糖二磷酸羧化酶加氧酶（Rubisco）是光合生物中最主要的自养羧化酶。Rubisco的加氧酶活性导致产生细胞毒性磷酸乙醇酸，并通过光呼吸去除。光呼吸释放出之前固定的二氧化碳，导致生长所需的碳净损失。C4光合作用使CO2相对于O2集中在Rubisco周围，从而消除Rubisco加氧酶活性。C4碳浓缩机制的一个基本特征是空间分离的初始固定CO2的磷酸烯醇式丙酮酸羧化酶在mesopyll细胞从二次再固定CO2的Rubisco在维管束鞘（BS）细胞周围的维管组织。最初的固定产生C4酸，其被运输到BS细胞，在那里它被脱羧，使Rubisco周围的CO2增加15倍。本研究的目的是检验我们的假设，C4光合叶结构的进化C3光合祖先来自顺式和反式调节的分歧，参与组织图案，细胞和质体分裂/扩张，胞间连丝和VT的形成，生长素的生物合成，信号和运输的基因。我们将确定的时空系列事件引起的细胞/组织结构的C4光合叶，光合功能是必不可少的。四翅滨藜（Atriplex prostrata（C3））、滨藜（A. rosea（C4）及其C3 xC 4 F1杂种将在我们实验室已经获得的RNA-seq/基因组数据的背景下进行和分析。我们将确认3-D模式的细胞分裂/扩张，以及叶绿体/胞间连丝的发展在M和BS细胞。这些功能将获得使用共聚焦显微镜，连续块面扫描电子显微镜，高分辨率透射电子显微镜的薄切片和免疫检测的蛋白质和定位的活性氧H2 O2与透射电子显微镜。 将使用抗体进行免疫组织化学，以检测参与组织图案形成、细胞和质体分裂/扩增以及胞间连丝形成的生长素和蛋白质。C4光合作用已经独立进化了60多次，使其成为生物界进化趋同的最佳例子之一。C4光合作用占陆地总初级生产力的23%，尽管它只发生在3%的植物物种中。尽管C4光合作用的重要性，我们对C4进化的细胞和分子控制的理解还处于起步阶段。从我们的研究结果将使C4叶结构/功能和这些基因的调控所必需的关键基因的鉴定。为了维护全球粮食安全，到2050年谷物产量必须增加70%。我们的研究将提供信息，通过将C4途径工程化到C3作物中来帮助维护全球粮食安全，就像现在在水稻中所做的那样。