Characterization of Xyloglucan Galactosyltransferase Homologs in Arabidopsis

University Of Connecticut, Storrs CT

Investigators

Abstract

The extracellular matrix (or "cell wall") of higher plants plays numerous protective and growth-regulating roles during the life cycle of a plant. Furthermore, plant cell wall material represents the most abundant source of newly synthesized biomass on earth making it an important renewable source of energy, and the raw material for industrial applications ranging from textile production to wood processing. Despite this importance of plant cell walls both from a basic and applied point of view, little is known about the synthesis of cell wall material on the molecular level. Plant cell walls consist primarily of polysaccharides representing long strings of sugar moieties that are attached to each other by enzymes referred to as glycosyltransferases. One of the most important and challenging areas in plant cell wall research is the identification of genes encoding these glycosyltransferases, and the determination of their function. To address this issue by a genetic approach, mutants of the plant model organism Arabidopsis thaliana were isolated which showed alterations in the composition of their cell wall material. One of these mutants turned out to be unable to synthesize normal xyloglucan (the major hemicellulose in most higher plants) because of a defect in a specific glycosyltransferase. An evaluation of the Arabidopsis genome sequence indicated the presence of ten coding regions with substantial structural similarity to this enzyme. These ten genes are expected to encode additional glycosyltransferases in cell wall synthesis. In our future research, the functions and properties of most of these enzymes will be investigated via three complementary approaches: (A) Determination in which parts of the plant these predicted glycosyl-transferases reside. (B) The identification of mutant lines which are defective in the activity of these enzymes. This will be followed by an analysis of their cell wall composition and an evaluation for changes in growth habit, physiology, and wall properties. (C) Production of the predicted glycosyltransferases in microorganisms followed by enzyme assays to determine their functions. The proposed experiments are designed to further our understanding of cell wall synthesis in higher plants with the potential to manipulate the cell wall composition of important crop plants to improve digestibility of forage crops, facilitate the production of fibers for paper products and clothing, and to improve the properties of cell wall components in human nutrition.