Molecular Biology and Developmental Functions of Wall Extension Proteins (Expansins) in Plant Cell Enlargement

PI的实验室已经从黄瓜下胚轴壁中鉴定并表征了两种蛋白质（“膨胀蛋白”），它们似乎介导了分离植物细胞壁的酸延伸反应。本建议概述了一个五年计划，以研究这些蛋白质的发育功能，并阐明其作用机制。该提案有五个主要目标。a)克隆黄瓜中2个扩增蛋白基因和拟南芥中1个扩增蛋白基因并对其进行测序，确定扩增蛋白活性位点的保守序列；b)在mRNA水平上分析扩增素基因表达的时空格局，并将其与生长发育模式联系起来；c)构建扩增素表达水平降低或提高的转基因植株，并分析由此产生的表型变化；d)绘制拟南芥基因图谱，检测先前鉴定的拟南芥生长突变体是否缺乏扩增素；e)在大肠杆菌中表达扩增素基因，作为验证基因身份的手段，并作为分离细胞壁和活细胞研究的蛋白质来源。这项研究很重要，因为它将确定这类新蛋白质在植物生长中的作用。膨胀蛋白是迄今为止发现的唯一能够在分离的植物细胞壁中诱导扩展的壁蛋白。这些蛋白质介导的生长反应似乎在具有纤维素壁的细胞中很常见，它可能有助于生长素刺激的生长。了解扩张蛋白的作用及其作用机制，将有助于揭示植物生长过程中细胞壁变化的分子基础。*** {7 u {!Z !Z Z ！F {{(Times New Roman Symbol & & Arial ' ' ' ' U ' ' h % 5 Geza Hrazdina博士

9317864 Cosgrove The PI's laboratory has identified and characterized two proteins ("expansins") from cucumber hypocotyl walls that appear to mediate the acid-extension response of isolated plant cell walls. This proposal outlines a five year plan to investigate the developmental functions of these proteins and to elucidate the mechanism of their action. The proposal has five major objectives. These are: a) to clone and sequence the two expansin genes from cucumbers and one expansin gene from Arabidopsis, and to identify conserved sequences that may code for the active site of the expansins; b) To analyze the spatial and temporal patterns of the expansin gene expression at the mRNA level and to relate these to developmental patterns of growth; c) To construct transgenic plants with reduced or enhanced levels of expansin expression and to analyze the resulting alterations in phenotype; d) To map the Arabidopsis gene and test whether previously identified Arabidopsis growth mutants are deficient in expansin production; e) to express an expansin gene in E. coli as a means of verifying gene identity and as source for protein for studies on isolated cell walls and living cells. %%% This study is important because it will establish the role of this novel class of proteins in plant growth. Expansins are the only wall proteins found to date that have the ability to induce extension in isolated plant cell walls. The growth response these protein mediate seems to be common in cells with cellulosic walls and it may contribute to auxin-stimulated growth. The understanding of the role of expansins and their mech anism of action will most likely lead to important discoveries of the molecular basis of plant cell wall changes during plant growth. *** { 7 u { ! Z ! Z Z ! F { { ( Times New Roman Symbol & Arial ` ` U " h % 5 Dr. Geza Hrazdina Dr. Geza Hrazdina