Regulation and Functions of the Arabidopsis XET Gene Family

William Marsh Rice University, Houston TX

Investigators

Abstract

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.