Cellulose is the structural component of the plant cell wall and the most abundant natural polymer on earth. It is produced by cellulose synthase, a large multi-subunit complex that resides in the plasma membrane. Genetic studies using the model Arabidopsis have led to the identification of proteins comprising the cellulose synthase machinery as well as critical enzymes and cytoskeletal proteins that interact with the core complex. A potential role for additional factors such as membrane lipids or sterols is intriguing but has not yet been adequately explored. Previous studies demonstrated that sterol composition is crucial for cellulose synthase activity. Yet, the molecular mechanisms by which sterols influence cellulose synthesis are not understood to date. In this project two debated hypotheses to explain the connection between sterols and cellulose synthesis will be tested. The first is that steryl glucosides, an abundant class of sterol conjugates in plants, act as primers for synthesis by transferring glucose residues to the growing chain of cellulose microfibrils. Alternatively or in addition, sterols play a general role in cellulose synthesis, as integral components of detergent-resistant plasma membrane subdomains. Sterols may act to maintain the structure and integrity of transmembrane proteins, such as the subunits that comprise cellulose synthase. To determine which of these mechanisms occurs in the cell, the project will employ an interdisciplinary approach using the primary cell wall as a model. Genetics and chemical genetics, biochemistry and cell biology, in parallel with systems biology approaches spanning genomics, lipidomics and proteomics will be applied. Chemical inhibitors of enzymes in the sterol biosynthesis pathway and mutants of Arabidopsis will be used as tools to dissect the membrane requirements for cellulose synthase function. The ultimate goal of this project is to elucidate the molecular link between sterols and cellulose synthesis in building the cell wall. This research is expected to result in transformative advances in understanding cellulose synthesis, and has strong potential to uncover novel insights in the dynamic interplay between sterols and proteins in the plasma membrane of plant cells.
Broader Impacts: This research will have broader impacts through the multi-disciplinary education of a postdoctoral scholar, graduate and undergraduate students. Underrepresented groups will be recruited through programs for McNair Scholars, Summer Undergraduate Research Opportunity, and Louis Stokes Alliance for Minority Participation. K-12 outreach will be achieved by partnerships with local teachers and programs for girls with interests in science, technology, engineering and mathematics careers. Through an international collaboration with a laboratory in Sweden, this project has broader impacts in training the next generation of US scientists with a global perspective. The information gained from this research will facilitate improvements in plant-derived products and biomass-related applications in biotechnology. Deciphering how the membrane environment influences cellulose synthase machinery may lead to knowledge concerning the digestibility of cellulose and the amount of cellulose that is produced in the cell wall, which are key considerations in engineering bioenergy crops of the future.