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

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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.