Regulation of cellulose synthase assembly and cellulose microfibril structure by STELLO proteins

Cellulose, a major component of plant cell walls, provides strength to plant cell walls and is the most abundant organic polymer on Earth. Its application in everyday life is widespread, exemplified by our large-scale use of cotton, paper and timber. The applications are increasing for cellulose prepared from plant cell walls, replacing fossil oil-derived materials. For example, it can be used as a thickener in food and paints, and to make new textiles that might replace synthetic, plastic fabrics. Yet there are many aspects of cellulose biology and cellulose structure that are not understood. A better understanding of the cellulose fibres, how they are made, and how they differ in different plants, will help us make best use of this renewable resource.
The molecular machine that spins cellulose fibres into the plant cell walls is a complicated structure. We recently discovered a new component of the machinery that makes cellulose in plants. In this research, we wish to understand how this new component, named STELLO, is able to influence the plant cellulose synthesis. In plants where STELLO does not work normally, we have found that the cellulose is defective. The plant walls are weak, and the components don't stick together normally. This discovery gives us an opportunity to study the effects on plants of having improper cellulose fibres in their walls. We will also exploit a newly developed technique, related to the magnetic resonance used in medicine, to study the shapes of cellulose and other cell wall molecules. With this technique we recently discovered how the material of the plant cell walls can assemble into fibres through precise complementarity of the molecular shapes, like pieces of a puzzle that snap together. In the plants without STELLO, it seems the shapes don't fit together properly. Studying this process therefore will reveal how the shape of cellulose is made, and in what ways it isimportant for plants and the materials we make from plants.

Cellulose, the major polysaccharide of the plant cell wall, provides strength to plant cell walls and is the most abundant organic polymer on Earth. Its application in everyday life is widespread, exemplified by our large-scale use of cotton, paper and timber. Yet there are many aspects of cellulose biology and cellulose structure that are not understood. Cellulose forms crystalline microfibrils that are embedded in walls of other polysaccharides, primarily xylan and glucomannan, plus lignin. The mechanism of interaction of cellulose microfibrils with the hemicelluloses in the secondary plant cell wall is not well understood, but this team recently showed, using solid-state NMR of Arabidopsis and mutants, that xylan and cellulose assemble in the wall through complementarity of their shapes.
We recently discovered STELLO, a Golgi-localised putative glycosyltransferase, that is important for correct cellulose fibril synthesis. STELLO appears to regulate cellulose synthase complex assembly and trafficking. This discovery reveals an unexpected regulation of the cellulose synthesis machinery through an unknown glycosylation process in the plant Golgi apparatus. In this program of research, we will study the defective cellulose in the stl mutants using a new and robust solid-state NMR technique applied in our team to intact plant secondary cell walls. Preliminary evidence suggests that the cellulose fibrils are defective in shape such that xylan cannot bind in the normal way, disrupting cell wall assembly. We will investigate further the hypothesis that STELLO is a glycosyltransferase that glycosylates cellulose synthesis proteins (CESAs). We will study how assembly and trafficking of the cellulose synthesis complex is affected by loss of STELLO protein and mutation of STELLO glycosylation activity. Through this research, we aim to reveal how a process of Golgi glycosylation regulates cellulose synthase assembly and cellulose microfibril structure.

Impact goals: The research team recognizes that both in the UK and globally we face significant challenges in producing sustainable and cost-effective materials from plant biomass. We aim to assist industry in development of sustainable biomass applications. We also aim to inform the public about the scientific basis of timber strength, the molecular basis of wood and paper, and also the applications of renewable plant materials. Additionally we aim to inspire children and school pupils to study and appreciate plant science as a way to promote sustainable materials of the future.

Industry stakeholders.
-Paper and pulp industry, through better understanding of timber and pulping processes (Stora Enso).
-Forestry companies through better breeding strategies, and better wood analysis techniques (Scion, New Zealand, and Innventia (RISE), Sweden).
-Timber for building construction through understanding wood processing, such as acetylation (Accoya, Stora Enso).
-Biorefining industry through better understanding of enzyme substrates (Novozymes).
-Cellulosic bioenergy industry though better process development for saccharification of sugar cane bagasse (Granbio, Brazil)
-Advanced biomaterials industry (various companies via Wallenberg Wood Science Centre).
-Crop breeders interested to reduce lodging and increase forage digestibility.

Society stakeholders.
-Local and national public and school children attending outreach events (Cambridge Science week events March annually, Cambridge Fascination of plants in Botanic Garden, May annually, Royal Society London Science Week)
-Children and school pupils will be inspired to study and value plant science and sustainable renewable materials.

To achieve these goals we will follow our pathways to impact plan.