Elucidation of molecular mechanism by which plant constructs cell-type specific cell-wall architecture

木葡聚糖内转糖苷酶/水解酶（XTHs）是一类与纤维素/木葡聚糖框架的构建和重组有关的酶。在拟南芥的基因组中发现了33个XTH基因家族成员，但它们的作用尚不清楚。在本研究中，我们分析了4个拟南芥XTH基因AtXTH17、-18、-19和-20的启动子：：GUS融合结构的组织特异性和生长阶段依赖性表达谱，这4个基因在系统发育上彼此密切相关。AtXTH17和AtXTH18表达于根的伸长和分化区，而AtXTH19表达于根尖的分裂和伸长区以及分化区，并被生长素上调表达。相比之下，AtXTH20在根基部成熟区的维管组织中特异性表达。该表达分析还揭示了四个基因中保守的顺式调控序列，并负责根特异性表达谱。接下来，我们检查了每个拟南芥XTH基因被破坏的突变体的表型，以确定该基因家族每个成员的作用，这是使用反向遗传方法进行的，并揭示了两个AtXTH27基因的功能缺失突变，xth27-1和xth27-2。它们在第一片叶片上显示出短形的管状分子，减少了第三脉的数量。在突变体成熟的莲座叶中，也观察到黄色的类似病变的斑点。pXTH27::GUS融合基因在莲座叶的未成熟气管元件中广泛表达。AtXTH27 mRNA在莲座叶片中表达量最高的时期为叶片膨大时期，即管状组织伸长时期。这些结果表明，AtXTH27在拟南芥莲座叶气管元件的产生过程中发挥了重要作用。这些结果表明，四个由基因复制产生的XTH基因在根内的表达谱多样化，从而在细胞壁动力学中承担特定的生理作用。少

Xyloglucan endotransglucosylase/hydrolases (XTHs) are a class of enzymes that are implicated in the construction and restructuring of the cellulose/xyloglucan framework. Thirty-three members of the XTH gene family are found in the genome of Arabidopsis thaliana, but their roles remain unclear. In this research we have analyzed the tissue-specific and growth stage-dependent expression profiles of promoter::GUS fusion constructs for four Arabidopsis XTH genes, AtXTH17, -18, -19, and -20, which are phylogenetically closely related to one another. AtXTH17 and AtXTH18 were expressed in all cell types in the elongating and differentiating region of the root, while AtXTH19 was expressed in the apical dividing and elongating regions, as well as in the differentiation zone, and was up-regulated by auxin. In contrast, AtXTH20 was specifically expressed in vascular tissues in the basal mature region of the root. This expression analysis also disclosed cis-regulatory sequences that are conserved a … More mong the four genes, and are responsible for the root-specific expression profile. Next, we examined phenotypes of mutants in which each of the Arabidopsis XTH genes was disrupted, to identify the role of each member of this gene family, This was undertaken using a reverse genetic approach, and disclosed two loss-of-function mutants for the AtXTH27 gene, xth27-1 and xth27-2. These exhibited short-shaped tracheary elements in tertiary veins, and reduced the number of tertiary veins in the first leaf. In mature rosette leaves of the mutant, yellow lesion-mimic spots were also observed. Extensive expression of the pXTH27::GUS fusion gene was observed in immature tracheary elements in the rosette leaves. The highest level of AtXTH27 mRNA expression in the rosette leaves was observed during leaf expansion, when the tracheary elements were elongating. These findings indicate that AtXTH27 plays an essential role during the generation of tracheary elements in the rosette leaves of Arabidopsis. These results indicate that the four XTH genes, which were generated by gene duplication, have diversified their expression profile within the root in such a way to take responsibility for particular physiological roles in the cell wall dynamics. Less