Molecular genetics and biochemistry of plant cell wall biosynthesis

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A defining characteristic of plants is the presence of cell walls, which surround all plant cells and are essential for their functions. They control plant growth and shape by determining the cell shape, but also serve specialized roles such water transport, providing rigidity to organs such as stems, and protection from the environment to cells at plant surfaces. Walls with water-conducting and structural functions are deposited in the cells of stem and root vascular and fibre systems, and are termed "secondary walls" since they are deposited after primary walls. Secondary walls can be massive and account for the bulk of the biomass of many plants, especially trees (wood is composed mostly of secondary walls). Since this biomass represents the renewable accumulation of enormous amounts of chemical energy, derived from solar energy via photosynthesis, there is intense interest in these materials not only for structural purposes, but also as a source of non-fossil fuel-derived energy. Secondary cell walls are complex composite structures, containing three major polymers, the carbohydrate polymers cellulose and hemi-cellulose, and lignin, a heavily cross-linked polymer based on phenolic rings. The relative abundance and structures of these polymers has a large impact on wood and fibre properties and their commercial uses. The processes by which secondary wall polymers are synthesized and how this process regulated at the genetic level is still not well understood. We will use two systems, the model small plant Arabidopsis and fast growing poplar trees, to investigate the regulation of secondary cell wall biosynthesis and deposition, focusing on the genes and proteins in a cellular regulatory circuit that appears to fine-tune amount of secondary cell wall deposition according to resources available to the plant. We will also investigate the properties and biosynthesis of the cell wall that coats pollen grains. Pollen walls consist mostly of a polymer called sporopollenin, one of nature's toughest and most durable matrices. Relatively little is known sporopollenin structure and deposition. We will use genetics, biochemistry and advanced imaging technology to address these questions, providing new understanding of this important biological material.