Plants are composed of a collection of cells whose varied shapes determines the final shape, size and growth characteristics of the entire plant. Each cell is surrounded by a structure called the cell wall, which is made up of carbohydrates and proteins manufactured by the cells. This cell wall must enlarge and be modified during cell growth and division, and the regulation and monitoring of its production and modification is critical to plant form and function. This work investigates a molecule, called WAK for Wall Associated Kinase, that is on the surface of plant cells that allows connection and communication between the cell and its cell wall, so that the cell growth and shape can be correctly regulated. WAK is a protein that traverses from the interior of cells to the outside where it binds pectins in the cell wall. Plants that lack WAK are deficient in cell growth. Experiments using Arabidopsis, a rapidly growing experimentally tractable plant, will include biochemical and genetic analysis of WAKs and WAK binding molecules to understand how the cell and its wall are connected, and the mechanism of information transfer. The work will be carried out at an undergraduate institution where the participating students will be provided with an integrative approach to science, and be prepared for the challenges of graduate and professional schools upon graduation.
Plants start their life as a seed and grow into sizes and shapes that are widely different, and can live in a variety of types of climates and soils. Each type of plant is genetically programmed to grow the way it does, but also to respond to changes in its surroundings, be it harsh weather, changes in soils, alterations in neighboring plants that might shade, or invasion by a pathogen or physical damage. All of these requirements involve the surface of the plant, or a part of the plant called the cell wall that surrounds all cells. This cell wall must expand or change shape as the cells inside the plant dictate. Conversely, as the cell wall is challenged, the cell within must be able to respond. Cell walls are composed in part of cellulose, and a variety of other carbon polymers, one of which is pectin. Pectin is a major commercial product for food substances in our world, but is also a major player in giving cell walls their strength, shape and characteristics. Each of the many thousands of cells that make up a plant are covered in a mesh of pectin, and are able to sense the state of the pectin. This is important as changes in pectin indicate a change outside of cell, be it fragmentation by pathogens or stretching by movement of the plant. The work in this grant established the protein molecule that binds to the pectin of the plant cell wall. This protein is a pectin receptor call WAK, short for Wall Associated Kinase. WAKS bind pectin out side of the cell, and have a part of their structure also inside the cell, where they can transmit the behavior of pectin. Thus when a pathogen arrives and fragments the pectin, WAKs relay this signal to the cell, which can then respond in a defensive manner. But WAKs also convey healthy signals to the cell, such that the cell can respond by continuing its growth.
