STUDIES ON ROLES OF GENES INVOLVED IN CELL-WALL CONSTRUCTION DURING PLANT MORPHOGENESIS

为了深入了解XTH（xyloglucan endotransglucosylase/hydrolase）基因家族的功能多样性，我们分析了它们的表达谱，得到如下结果：1）两个红豆VaXTH基因具有基本相似但不同的组织特异性表达谱。VaXTH 1在节间基部的木质部细胞中表达，而VaXTH 2在木质部中很少或没有表达。此外，它们沿着节间表现出空间上不同的表达谱，VaXTH 1比VaXTH 2更靠近节间顶部表达，生长素上调两种mRNA水平，然而，生长素对VaXTH 1基因的这种作用在0.25 M甘露醇中无效，这防止了细胞扩增而不影响生长素作用本身。另一方面，生长素诱导的VaXTH 2基因的上调不受甘露醇的影响。2）我们使用定量实时RT-PCR检测了33个拟南芥AtXTH基因的表达谱，并发现大多数成员在组织特异性和对激素信号的响应方面表现出不同的表达谱，其中一些成员表现出相似的表达模式。3）对AtXTH 17、18、19和20进行了启动子分析，确定了与根特异性表达谱相关的顺式作用区。支持XTH基因家族的每个成员都受到不同植物激素组的特异性调节，并在特定组织中的特定发育阶段参与特定过程。基于这些考虑，我们提出了一个假设，在一定的细胞类型的细胞壁的构建，维持和重组的一系列协同行动的一组酶的细胞壁类型的特征。

To gain insight into the functional diversity of the XTH (xyloglucan endotransglucosylase/hydrolase) gene family, we analyzed their expression profiles and obtained the results as followes :1) The two azuki bean VaXTH genes exhibit essentially similar but different tissuespecific expression profiles. Whereas VaXTH1 is expressed in xylem cells in the basal part of the internode, little or no expression of VaXTH2 is found in the xylem. Furthermore, they exhibit spatially divergent expression profiles along the internode, VaXTH1 being expressed nearer to the top of the internode than VaXTH2Auxin up-regulates both of the mRNA levels, however, this effect of auxin on the VaXTH1 gene is nullified in 0.25 M mannitol, which prevents cell expansion without affecting auxin action per se. On the other hand, the auxin-induced up-regulation of the VaXTH2 gene is not affected by mannitol.2) We examined expression profiles of the 33 Arabidopsis AtXTH genes, using quantitative real-time RT-PCR, and revealed that most members exhibit distinct expression profiles in terms of tissue specificity and responses to hormonal signals, with some members exhibiting similar expression patterns. By comparing the flanking sequences of individual genes, we identified four sets of large-segment duplicatoins and two sets of solitary gene duplications.3) We have conducted promoter analysis of the AtXTH17, 18, 19 and 20 and identified cis-acting regions responsible for root specific expression profiles.The results obtained, thus far, support the idea that each member of the XTH gene family is regulated specifically by different sets of plant hormones, and is committed to a certain specific process in a specific tissue, at specific stages of development. Based on these considerations, we advance a hypothesis that the cell wall in a certain cell-type is constructed, maintained and restructured by a series of collaborative actions of a set of enzymes characteristic to the cell-wall type.