Characterization of Xyloglucan Galactosyltransferase Homologs in Arabidopsis

高等植物的细胞外基质（或“细胞壁”）在植物的生命周期中发挥着许多保护和生长调节作用。 此外，植物细胞壁材料代表了地球上最丰富的新合成生物质来源，使其成为重要的可再生能源，以及从纺织生产到木材加工的工业应用的原材料。 尽管从基础和应用的角度来看植物细胞壁的重要性，但在分子水平上对细胞壁材料的合成知之甚少。 植物细胞壁主要由多糖组成，多糖代表通过称为糖基转移酶的酶彼此连接的长串糖部分。 植物细胞壁研究中最重要和最具挑战性的领域之一是鉴定编码这些糖基转移酶的基因，并确定其功能。 为了通过遗传方法解决这个问题，分离了植物模式生物拟南芥的突变体，其显示出细胞壁材料组成的改变。 其中一个突变体由于一种特殊的糖基转移酶的缺陷而不能合成正常的木葡聚糖（大多数高等植物中的主要半纤维素）。 对拟南芥基因组序列的评估表明存在与该酶具有实质性结构相似性的10个编码区。 这十个基因预期编码细胞壁合成中的额外糖基转移酶。 在我们未来的研究中，大多数这些酶的功能和特性将通过三种互补的方法进行研究：（A）确定这些预测的糖基转移酶驻留在植物的哪些部分。 (B)鉴定这些酶活性缺陷的突变株系。 随后将对其细胞壁组成进行分析，并对生长习性、生理学和细胞壁特性的变化进行评价。 (C)在微生物中产生预测的糖基转移酶，然后进行酶测定以确定其功能。 提出的实验旨在进一步了解高等植物细胞壁合成的潜力，操纵重要作物植物的细胞壁组成，以提高饲料作物的消化率，促进纸制品和服装纤维的生产，并改善细胞壁组分在人类营养中的特性。

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.