Functional dissection of pectic rhamnogalacturonan-I (RG-I) in plant cell walls

植物细胞壁是所有植物细胞表面的刚性结构，负责产生生长中的植物和许多来自水果、蔬菜和纺织纤维等作物的产品/材料的机械性能。细胞壁是机械强度高的生物材料，在结构方面非常复杂。它们由一系列不同结构的多糖组成，包括纤维素、半纤维素和果胶多糖。植物细胞壁的果胶成分在结构上特别复杂，并与纤维素和其他多糖在细胞壁内缠绕。果胶在细胞壁组装中的作用以及细胞壁特性的产生导致植物材料特性的作用尚不清楚。果胶多糖的一部分是一种结构复杂和高度可变的多糖，被称为鼠李糖半乳糖醛酸- 1 (RGI)，因为它的结构主干含有糖鼠李糖和半乳糖醛酸。这种多糖骨架具有富含阿拉伯糖和半乳糖的侧链。RG-I结构域的个体结构似乎因细胞而异，一些证据表明，它们在产生细胞壁特性方面发挥作用，影响细胞和组织的延展性和坚固性等因素。该项目将开发一套新的工具来识别和跟踪使用模式植物系统拟南芥的单个RGI分子。这项在单叶或根的微观水平上产生RGI成分概况的工作将为植物生物学开辟一个新的领域，并有望控制植物材料的机械和纹理特性。该项目将使用该方案第一部分开发的分析方法来研究RGI在植物生长方面的结构和功能。生长中的植物必须承受一系列的机械压力——无论是风和雨，不断地给嫩芽和叶子施加压力，还是在不同密实度的土壤中生长的根。尽管初步证据表明RGI分子参与了细胞和器官的机制形成，也参与了对压力的反应，但关于细胞壁和植物器官如何对这些机械压力做出反应，我们知之甚少。本项目开发的RGI分析工具和方法将用于研究RGI分子在生长过程中受机械应力影响的变化和修饰。了解RGI如何影响细胞壁特性，如细胞壁的硬度和弹性，将为了解细胞壁特性是如何产生的提供重要的知识。这项工作将影响我们对一系列植物材料和产品的理解和开发能力，从苹果和番茄水果等食用产品的质地到小麦谷物到棉纤维。它还将为农作物如何应对气候因素和环境压力施加的机械压力提供基础理解。

Plant cell walls are rigid structures at the surface of all plant cells and are responsible for generating the mechanical properties of growing plants and many products/materials derived from crops such as fruits, vegetables and textile fibres. Cell walls are mechanically strong biomaterials and are highly complex in terms of structure. They are comprised of varied configurations of a range of polysaccharides that include cellulose, hemicelluloses and pectic polysaccharides. The pectic components of plants cell walls are particularly structurally highly complex and are entwined within cell walls with the cellulose and other polysaccharides. The roles of pectin in cell wall assembly and the generation of cell wall properties leading to the properties of plant materials are not understood. A portion of the pectic polysaccharides are a structurally complex and highly variable set of polysaccharides that are known as rhamnogalacturonan-I (RGI) due to the presence of a structural backbone that contains the sugars rhamnose and galacturonic acid. This polysaccharide backbone has side chains rich in arabinose and galactose sugars. The individual structures of RG-I domains appear to vary from cell to cell and several lines of evidence suggest that they have a role in generating cell wall properties influencing factors such as the extensibility and firmness of cells and tissues. The project will develop a new set of tools to identify and track individual RGI molecules using the model plant system Arabidopsis. This work in generating understanding of the profiles of RGI components at a microscale level in a single leaf or root will open up a new area for plant biology with the prospect of controlling the mechanical and textural properties of plant materials. The project will use the analytic methods developed in the first part of the programme to study RGI structure and functions in the context of plant growth. Growing plants have to withstand a range of mechanical stresses - whether this is wind and rain that constantly stress shoots and leaves or roots growing through soil with varying degrees of compactness. Little is known about how cell walls and plant organs respond to these mechanical stresses although preliminary evidence indicates that RGI molecules are involved generating the mechanics of cells and organs and also involved in responses to stress. The tools and approaches for RGI analysis developed in the project will be used to study the variation and modification of RGI molecules subject to mechanical stresses during growth. An understanding of how RGI impacts on cell wall properties such as firmness and elasticity to cell walls will generate important knowledge to understand how cell wall properties are generated. The work will impact on our understanding and capacity for exploitation of a range of plant materials and products from texture of eaten products such as apple and tomato fruits to wheat grain to cotton fibres. It will also provide underpinning understanding of how crop plants respond to mechanical stress imposed by climatic factors and environmental stresses.