Function of Arabidopsis thaliana Proline Rich Proteins in Root Hairs and Guard Cells of Arabidopsis

植物细胞壁是一种动态结构，可以根据发育和环境信号进行修饰。通过这种方式，细胞壁提供了在植物生长过程中帮助维持细胞形态和功能的结构信息。细胞壁的结构也会因病原体感染和逆境（如干旱、高盐和低温）而发生变化，从而帮助植物在自然环境中生长时免受生物和非生物胁迫。细胞壁中许多结构蛋白的表达已被证明具有细胞类型特异性，这表明这些蛋白在修饰细胞壁结构方面发挥着新的作用，以提供机械强度并协助细胞壁的正常组装。脯氨酸富蛋白（PRPs）是一个完整的细胞壁结构蛋白家族，其表达与许多植物系统的活性生长有关。我们使用PRP启动子/ gus融合和表位标记的组合来表征这些基因在拟南芥中的表达及其在特定细胞类型壁上的定位。其中两种蛋白，AtPRP1和AtPRP3，在根毛生长的早期阶段表达，但定位于根毛细胞壁的不同区域。这些结果表明，单个PRP基因家族成员可能在帮助根毛细胞壁组装过程中建立壁结构方面发挥了不同的作用。此外，我们已经证明atprp4在保护细胞中表达，并定位于保护细胞壁的内层。我们已经分离出了这三种蛋白的几个T-DNA插入等位基因，我们建议表征这些与根毛和保护细胞功能相关的突变体的功能缺失表型。此外，我们将研究表位标记的prp序列在野生型和突变型prp背景下在细胞壁内交联的能力。综上所述，这些实验方法应提供新的见解，以了解编码在单个AtPRPs内的氨基酸序列的性质，这些氨基酸序列足以在细胞壁内靶向定位和在细胞外基质内不溶化。鉴定结构细胞壁蛋白在确定细胞类型特异性基质结构中的功能是我们能够修改植物细胞壁以使其在不利环境中生长的重要的第一步。我们已经证明AtPRP蛋白参与决定保护细胞和根茎的细胞壁结构，这两种细胞类型在生长过程中对营养吸收和维持水分平衡至关重要。对这些蛋白功能的进一步分析可能使我们能够设计出在水分和/或营养限制条件下促进植物生长的新机制。

The plant cell wall is a dynamic structure that can be modified in responseto developmental and environmental signals. In this manner, the cell wallprovides structural information that helps maintain cellular form andfunction during plant growth. The structure of the cell wall also changesin response to pathogen infection and stresses, such as drought, high saltand cold temperature, in a manner that helps protect plants from biotic andabiotic stresses when grown in natural environments. Expression of many ofthe structural proteins in the wall have been shown to be cell-typespecific, suggesting that these proteins play novel roles in modifying cellwall structure in order to provide mechanical strength and assist in properwall assembly.Proline-rich proteins (PRPs) represent an integral family of structuralcell wall proteins whose expression has been linked to active growth in anumber of plant systems. We have used a combination of PRP promoter/GUSfusions and epitope-tagging to characterize the expression of these genesin arabidopsis and their localization to the walls of specific cell types.Two of these proteins, AtPRP1 and AtPRP3, are expressed during the earlystages of root hair outgrowth but are localized within different regions ofthe root hair cell wall. These results suggest that individual PRP genefamily members may play distinct roles in helping to establish root haircell wall structure during wall assembly. In addition, we have shown thatAtPRP4 is expressed in guard cells and localizes to the inner shelf of theguard cell wall. We have isolated several T-DNA insertion alleles forthese three proteins and we propose to characterize the loss-of-functionphenotypes in these mutants associated with root hair and guard cellfunction. In addition, we will examine the ability of epitope-tagged PRPsequences to become cross-linked within the wall in wild type and mutantPRP backgrounds. In combination, these experimental approaches shouldprovide new insight into the nature of the amino acid sequences encodedwithin individual AtPRPs that are sufficient for their targetedlocalization within the cell wall and their insolubilization within theextracellular matrix.Identification of the function of structural cell wall proteins in definingcell-type specific matrix structures is an important first step in ourability to modify the cell walls of plants in a manner that will let themgrow in adverse environments. We have shown that the AtPRP proteinsparticipate in determining cell wall structure in guard cells and roothairs, two cell types that are crucial for nutrient uptake and maintenanceof water balance during growth. Further analysis of the function of theseproteins may allow us to devise novel mechanisms for enhancing plant growthunder conditions of water and/or nutrient limitation.