Analysis of cell wall construction processes using transgenic plants

植物细胞壁在形态建成和对环境信号的响应中起着重要作用。木葡聚糖是植物细胞壁基质的主要成分，并作为纤维素微纤丝之间的交联物以形成纤维素木葡聚糖框架。内切木葡聚糖转移酶（EXGT）是一种介导木葡聚糖分子间分子接枝反应的酶，我们于1992年对其进行了分离和鉴定。虽然对编码EXGT的cDNA的结构研究强烈表明它们在细胞壁结构构建中的重要作用，但它们的生理作用仍然未知。本研究以转基因拟南芥和烟草BY-2细胞为材料，分离EXGT蛋白和基因，分析其酶的作用方式和表达谱。拟南芥EXGT-A1基因的启动子/ GUS融合基因分析表明，该基因在所有器官中表达，并优先在次生细胞壁广泛沉积的细胞中表达。编码结构上相关的EXGT-A1蛋白的拟南芥cDNA的分离显示存在相当大的木葡聚糖相关蛋白（XRP）的多基因家族。数据表明，不同的XRP基因可能表现出潜在的不同表达谱方面的组织特异性和响应激素和机械信号。烟草EXGT-N1蛋白对木葡聚糖表现出水解酶和转移酶活性。这些结果有力地表明，每个XRP功能作为水解酶或转移酶作用于木葡聚糖，并共享在不同的细胞和组织中的细胞壁构建和修饰的作用。

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.