Plant cells produce an extracellular matrix, the cell wall, that determines and maintains the shape of cells and serves a protective barrier. Plant cell walls are highly complex structures composed predominantly of a diverse set of polysaccharides that vary in structure and abundance. Cellulose is the most abundant polysaccharide on earth, followed by xylan, a hemicellulosic component of the plant cell wall. Characterisation of the different polysaccharides synthesised in plant species dates back to the early 19th century. However, apart from cellulose, enzymes catalysing the synthesis of the majority of other cell wall polysaccharides are still uncharacterised or even undiscovered. Recently, plant polysaccharides edge ever closer to the spotlight, as they provide a sustainable resource for energy production. They are also essential for nutritional value and other beneficial traits of food.
Figure 1: A model of polysaccharide biosynthesis in the Golgi
The biosynthesis of polysaccharides involves the action of hundreds of different glycosyltransferases (GTs), the enzymes that catalyse the specific transfer of sugar moieties from activated nucleotide sugar donors to acceptor molecules, forming glycosidic bonds. Specific nucleotide-sugar transporters located in the Golgi membrane are also involved as suppliers of the monosaccharide (Figure 1). Our knowledge about the specific function of the glycosyltranferases and the requirement of specific sugar transporters for biosynthesis is, however, limited.
At the moment we are predominantly working on understanding the biosynthesis of diverse variants of xylan and glucomannan in different plants. Both xylan and glucomannan are hemicellulosic components of the plant cell wall that are synthesized in the Golgi apparatus. In general, our research focuses on understanding how the polysaccharides are synthesized, what their structure is and how the structure relates to function. Recently published work on xylan biosynthesis and glucomannan biosynthesis exemplifies our approach of combining reverse genetics, cell biology and biochemical methods to analyse protein function and polysaccharide structure. The complexity of polysaccharide structures and their analysis are exemplified by our work on the structure of arabinogalactans.