Baumberger N, Steiner M, Ryser U, Keller B, Ringli C
Institute of Plant Biology, University of Zürich, Zollikerstrasse 107, CH-8008 Zürich, Switzerland.
Plant J. 2003 Jul;35(1):71-81. doi: 10.1046/j.1365-313x.2003.01784.x.
LRR-extensins (LRX) form a family of structural cell wall proteins containing a receptor-like domain. The functional analysis of Arabidopsis LRX1 has shown that it is involved in cell morphogenesis of root hairs. In this work, we have studied LRX2, a paralog of LRX1. LRX2 expression is mainly found in roots and is responsive to factors promoting or repressing root hair formation. The function of LRX1 and LRX2 was tested by the expression of a truncated LRX2 and different LRX1/LRX2 chimaeric proteins. Using complementation of the lrx1 phenotype as the parameter for protein function, our experiments indicate that LRX1 and LRX2 are functionally similar but show differences in their activity. Genetic analysis revealed that single lrx2 mutants do not show any defect in root hair morphogenesis, but synergistically interact with the lrx1 mutation. lrx1/lrx2 double mutants have a significantly enhanced lrx1 phenotype, resulting in frequent rupture of the root hairs soon after their initiation. Analysis of the root hair cell wall ultrastructure by transmission electron microscopy (TEM) revealed the formation of osmophilic aggregates within the wall, as well as local disintegration of the wall structure in the double mutant, but not in wild-type plants. Our results indicate that LRX1 and LRX2 have overlapping functions in root hair formation, and that they likely regulate cell morphogenesis by promoting proper development of the cell wall.
富含亮氨酸重复序列的伸展蛋白（LRX）构成了一个包含类受体结构域的结构性细胞壁蛋白家族。对拟南芥LRX1的功能分析表明，它参与根毛的细胞形态发生。在这项研究中，我们研究了LRX1的旁系同源蛋白LRX2。LRX2的表达主要在根中发现，并且对促进或抑制根毛形成的因子有反应。通过表达截短的LRX2和不同的LRX1/LRX2嵌合蛋白来测试LRX1和LRX2的功能。以lrx1突变体表型的互补作为蛋白质功能的参数，我们的实验表明LRX1和LRX2在功能上相似，但在活性上存在差异。遗传分析表明，单个lrx2突变体在根毛形态发生上没有表现出任何缺陷，但与lrx1突变协同作用。lrx1/lrx2双突变体具有显著增强的lrx1表型，导致根毛在起始后不久频繁破裂。通过透射电子显微镜（TEM）对根毛细胞壁超微结构的分析显示，双突变体的细胞壁内形成了嗜渗性聚集体，以及细胞壁结构的局部解体，而野生型植物中则没有。我们的结果表明，LRX1和LRX2在根毛形成中具有重叠功能，并且它们可能通过促进细胞壁的正常发育来调节细胞形态发生。
