Regulation and Functions of the Arabidopsis XET Gene Family

细胞壁是植物细胞的基本结构，它控制细胞的形状、大小和完整性，并在信号转导中发挥作用。修饰壁多糖的酶可能调节壁结构，从而在植物的形态发生和生理中发挥关键作用。木葡聚糖内糖基转移酶(XETs)能够修饰细胞壁的主要成分，但这些酶的生理功能尚不清楚。植物含有编码XET和XET相关蛋白的基因家族；这些酶的复杂性和保守性表明这些酶可能在植物细胞生物学中发挥至关重要的作用。通过拟议的研究将回答以下问题：1.拟南芥XET家族有多复杂，XET一级结构有哪些独特和共有的特征？2.失去单个和多个XET的生理后果是什么？3.XET在何时何地表达，蛋白质的模式和运动是什么？4.XET在生化活动上有何相似和/或不同，哪些结构特征对酶功能可能是重要的？由于基因家族的存在，对XET功能的剖析将需要一种广泛的、综合的方法。拟南芥的XET和XET相关基因将根据一级结构进行鉴定和分类。将寻找XET基因内的突变和突变表型，除了壁属性和适应不同环境的能力外，还表现在生长、发育和整体适应能力方面。XETs的表达模式和诱导行为将被阐明。报告基因融合将能够确定组织、器官、细胞和表达的发育特异性。此外，记者将被用来定义蛋白质的定位和潜在的运动。将使用异源表达系统来生产酶，并将评估和比较不同同工酶之间的性质，如底物偏好和反应条件。通过这项工作，将阐明拟南芥复杂的XET基因家族的调控和功能。这些实验的完成将使我们深入了解细胞壁是如何形成、维持和修改的，以及这些特性如何影响植物的整体适应性、发育和生理。

The cell wall is a fundamental structure of plant cells that controls cellular shape, size and integrity and also plays a role in signal transduction. The enzymes that modify wall polysaccharides are likely to regulate wall structure and thus play critical roles in plant morphogenesis and physiology. The xyloglucan endotransglycosylases (XETs) are capable of modifying a major component of the cell wall and yet the physiological functions of these enzymes are not understood. Plants harbor gene families that encode XETs and XET-related proteins; the complexity and conservation of these enzymes indicate that these enzymes likely carry out critically important roles in plant cell biology. The following questions will be answered through the proposed studies:1. How complex is the Arabidopsis XET family, and what are the unique and shared features of XET primary structures?2. What are the physiological consequences of the loss of single and multiple XETs?3. When and where are the XETs expressed, and what are the patterns and movements of the proteins?4. How are the XETs similar and/or distinct in biochemical activities and what structural features may be important for enzymatic function? Because of the presence of a gene family, dissection of the functions of XETs will require a broad-based, integrative approach. The XET and XET-related genes of Arabidopsis will be identified and classified based on primary structure. Mutations within XET genes will be sought and mutant phenotypes characterized with respect to growth, development and overall fitness, in addition to wall properties and ability to adapt to diverse environments. Expression patterns and induction behaviors of the XETs will be elucidated. Reporter gene fusions will enable determination of tissue, organ, cell and developmental specificity of expression. In addition, reporters will be used to define the localization and potential movements of the proteins. Enzymes will be produced with a heterologous expression system, and properties, such as substrate preferences and reaction conditions, will be assessed and compared among the different isozymes. Through this work, the regulation and functions of the complex XET gene family of Arabidopsis will be elucidated. Completion of these experiments will provide insight into how cell walls are formed, maintained and modified, and how these properties impact the overall fitness, development and physiology of plants.