Molecular dissection of regulatory mechanism that controls cell-type specific cell wall construction using XTH family of genes as a model system

木葡聚糖内转糖基化酶/水解酶（XTHs）是一类能够催化木葡聚糖之间的分子接枝和/或木葡聚糖分子的内型水解的酶。它们在拟南芥中由33个基因编码。虽然最近的研究已经揭示了该家族个体成员在植物中的时间和空间特异性表达谱，但它们的生物学作用仍有待阐明。为了确定该基因家族每个成员的作用，我们检查了每个拟南芥XTH基因被破坏的突变体的表型。AtXTH27基因的两个功能缺失突变体xth27-1和xth27-2在第三脉中表现出短形管状元件，并减少了第一片叶子的第三脉数量。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。在XTH27 -1突变株中引入野生型XTH27基因进行遗传互补后，第三脉数量恢复，且病变完全消失。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。拟南芥XTH基因AtXTH17、18、19和20在系统发育上相互密切相关，并优先在根中表达。然而，它们在根内表现出不同的表达谱，对激素信号的反应也不同。为了研究它们在根系生长中的功能，我们使用T-DNA插入系和RNAi植物检测了这些基因的功能缺失突变体的表型。这些功能分析揭示了AtXTH18基因在主根伸长中的主要作用。在四个XTH基因中，AtXTH18的mRNA表达量最高。我们还利用AXR2/IAA7基因缺陷突变体确定了这些基因的生长素信号通路，发现根系伸长/成熟区AtXTH19的表达受AXR2/IAA7信号通路的控制。少

Xyloglucan endotransglucosylases/hydrolases (XTHs) are a class of enzymes capable of catalyzing the molecular grafting between xyloglucans and/or the endotype hydrolysis of a xyloglucan molecule. They are encoded by 33 genes in Arabidopsis. Whereas recent studies have revealed temporally and spatially specific expression profiles for individual members of this family in plants, their biological roles are still to be clarified. To identify the role of each member of this gene family, we examined phenotypes of mutants in which each of the Arabidopsis XTH genes was disrupted.Two loss-of-function mutants for the AtXTH27 gene, xth27-1 and xth27-2 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. Upon genetic complementation by introducing the wild-type XTH27 gene into xth27-1 mutant plants, the number of tertiary veins was restored, and … More the lesions disappeared completely. 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.The Arabidopsis thaliana XTH genes AtXTH17, 18, 19, and 20 are phylogenetically closely related to one another and are preferentially expressed in the roots. However, they exhibit different expression profiles within the root and respond to hormonal signals differently. To investigate their functions in root growth, we examined phenotypes of loss-of-function mutants for these genes using T-DNA insertion lines and RNAi plants. These functional analyses disclosed a principal role for the AtXTH18 gene in primary root elongation. Of the four XTH genes, AtXTH18 exhibits the highest level of mRNA expression. We also determined auxin-signaling pathways for these genes using a mutant with a defect in the AXR2/IAA7 gene and found that the expression of AtXTH19 in the elongation/maturation region of the root is under the control of the AXR2/IAA7 signaling pathway. Less