Osato Yasue, Yokoyama Ryusuke, Nishitani Kazuhiko
Graduate School of Life Sciences, Tohoku University, Sendai 980-8576, Japan.
J Plant Res. 2006 Mar;119(2):153-62. doi: 10.1007/s10265-006-0262-6. Epub 2006 Feb 14.
Rearrangement of cellulose microfibrils within cell-wall matrices is considered one of the most critical steps in the regulation of both the orientation and extent of cell expansion in plants. Xyloglucan endotransglucosylase/hydrolases (XTHs) are a family of enzymes that mediate the construction and restructuring of load-bearing cross links among cellulose microfibrils. 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.
纤维素微纤丝在细胞壁基质中的重排被认为是植物细胞扩展方向和程度调控中最关键的步骤之一。木葡聚糖内转糖基酶/水解酶（XTHs）是一类介导纤维素微纤丝之间承重交联构建和重组的酶。拟南芥XTH基因AtXTH17、18、19和20在系统发育上彼此密切相关，且在根中优先表达。然而，它们在根内表现出不同的表达模式，对激素信号的响应也不同。为了研究它们在根生长中的功能，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。在这四个XTH基因中，AtXTH18表现出最高水平的mRNA表达。我们还使用AXR2/IAA7基因有缺陷的突变体确定了这些基因的生长素信号通路，发现AtXTH19在根伸长/成熟区域的表达受AXR2/IAA7信号通路的控制。
