Analysis of cell wall construction processes using transgenic plants

植物细胞壁在形态发生和对环境信号的响应中起着核心作用。木葡聚糖是植物细胞壁基质的主要成分，是纤维素微纤维之间的交联剂，形成纤维素-葡聚糖骨架。内切葡聚糖转移酶(EXGT)是我们于1992年分离并鉴定的一种介导木聚糖分子间分子接枝反应的酶。虽然对编码EXGT的cDNA的结构研究强烈表明它们在构建细胞壁结构中具有重要作用，但它们的生理作用仍不清楚。在本研究项目中，我们分离了EXGT蛋白和基因，并利用转基因拟南芥植株和烟草BY-2细胞分析了它们的酶作用方式和表达谱。对拟南芥EXGT-A1基因启动子/GUS融合基因的分析表明，该基因在所有器官中都有表达，并且在次生细胞壁广泛沉积的细胞中优先表达。对拟南芥编码结构相关蛋白EXGT-A1的cDNAs的分离表明，存在一个相当大的木葡聚糖相关蛋白(XRP)多基因家族。数据表明，不同的XRP基因可能在组织特异性和对激素和机械信号的反应性方面表现出潜在的不同表达谱。烟草EXGT-N1蛋白对木葡聚糖具有水解酶和转移酶活性。这些结果有力地表明，每个XRP都作为作用于木聚糖的水解酶或转移酶发挥作用，并在不同的细胞和组织中共同参与细胞壁的构建和修饰。

The plant cell wall play a central role in morphogenesis as well as responsiveness to environmental signals. Xyloglucans are the principal component of the plant cell wall matrix, and serve as cross-links between cellulose microfibrils to form cellulosexyloglucan framework. Endoxyloglucan transferase (EXGT), which we isolated and characterized 1992, is an enzyme that mediates molecular grafting reaction between xyloglucan molecules. Although structural studies on cDNAs encoding EXGTs strongly suggest their important roles in construction of cell wall architecture, their physiological roles are still unknown. In this research project, we isolated EXGT proteins and genes, and analyzed their mode of enzyme action and expression profiles using transgenic Arabidopsis plants and tobacco BY-2 cells. Promoter / GUS fusion gene analysis for Arabidopsis EXGT-A1 gene has shown that this gene was expressed in all organs, and was preferentially expressed in cells where secondary cell wall was extensively deposited. Isolation of Arabidopsis cDNAs encoding proteins structurally related EXGT-A1 shows the presence of a fairly large multi-gene family of xyloglucan related proteins (XRP). Data suggested that different XRP genes may exhibit potentially different expression profiles with respect to tissue specificity and responsiveness to hormonal and mechanical signals. A tobacco EXGT-N1 protein exhibited both hydrolase and transferase activity toward xyloglucans. These results strongly suggest that each XRP functions either as hydrolase or transferase acting on xyloglucans, and share roles in cell wall construction and modification in different cells and tissues.