Characterization of Arabidopsis Mutants Altered in Fucose- Containing Cell Wall Polysaccharides

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9405739 Reiter In an effort to further understand the synthesis, structure and function of the plant cell wall, a direct biochemical screening procedure has been used to isolate mutants of Arabidopsis with alterations in their cell wall polysaccharide composition. Three different loci have been identified that either lead to the complete absence of L- fucose in cell wall material (mur1) or to an approximately 50% reduction in the amount of this monosaccharide (lines mur2 and mur3). To fully exploit the usefulness of these mutant lines, it is necessary to understand the biochemical or regulatory lesions leading to the mutant phenotypes, and to get access to the affected genes. The proposed research will use biochemical tools to define the changes leading to the observed alterations in cell wall composition. Experiments will be carried out to determine whether the mutant lines show defects in precursor availability, or whether they are deficient in some aspects of glycosyl transfer. These questions will be addressed by quantifying the amount of GDP- fucose (the substrate for fucosyltransferase) and by determining structural changes in fucose containing cell wall polysaccharides. The studies will be complemented by assaying fucosyltransferase activities , and the activity of enzymes in the de novo synthesis of GDP-L-fucose. All selected mutations will be mapped relative to molecular markers as a prerequisite to get access to the affected genes by map-based procedures. The mur1 mutation appears to be particularly amenable to genetic analysis because a large number of independent alleles is already available, and an easy immunological screening procedure can be used to construct a genetic map of high resolution. Accordingly, attempts will be made to clone the MUR1 gene either from tagged libraries or by map -based procedures. The availability of this gene would allow some insights into the regulation of sugar nucleotide interconversion pathways in hi gher plants, and permit the modification of cell wall composition in other plants including economically important species. %%% The cell walls of higher plants play pivotal roles during plant growth and development, and determine the physical properties of all parts of the plant. Examples include the softness of fruits, the strength of textile fibers, the digestibility of forage, and the processing characteristics of wood during paper production. Furthermore, plant cell walls present the interface between the plants and their environment and play important roles in the defense of plants against pests. Finally, plant cell wall material accounts for most of the newly synthesized terrestrial biomass, making it the most important renewable source of reduced carbon, which can be used as raw material for the chemical industry and for fuel production. Accordingly, it is highly desirable to understand the mechanism by which plant cell wall material is synthesized, and to get access to the genes controlling the properties of plant cell wall material. This will ultimately open up opportunities to use tools of biotechnology to modify plant cell walls in ways that are desirable from an economically and/or ecological point of view. ***