Marchantia: a simple model system to study cell wall biosynthesis
- School of BioSciences, University of Melbourne, Australia.
- School of Biological Sciences, Monash University, Australia.
- Department of Biology, Rhode Island College, USA.
- ARC Centre of Excellence in Plant Cell Walls, and School of Agriculture, Food and Wine, The University of Adelaide, Waite Campus, Australia.
- La Trobe Institute for Agriculture and Food, School of Life Sciences, La Trobe University, Australia.
The liverwort Marchantia polymorpha is a basal land plant with many of the key innovations seen in angiosperms. With little genetic redundancy in its genome, Marchantia is an ideal system for studying cell wall biosynthesis in plants. Its walls are mostly composed of cellulose with the main non-cellulosic polysaccharides being xyloglucan and heteromannan. To facilitate dissection of the genes involved in cell wall biosynthesis, we have constructed a library of Marchantia glycosyltransferases (GTs) and used it to unravel processes involved in cellulose biosynthesis. In angiosperms, such as Arabidopsis, cellulose is produced by large CELLULOSE SYNTHASE A (CESA) complexes (CSCs) that are embedded in the plasma membrane. Each CSC is heteromeric, being composed of the products of three or more CESA genes. By contrast, Marchantia has only two CESA genes with non-overlapping expression profiles. Freeze-fracture electron microscopy experiments show rosette-like structures in the plasma membrane, suggesting that Marchantia CSCs are homomeric. Loss of Marchantia CESA function leads to plantlets with severe growth defects linked to the loss of cellulose from their cell walls. Together, these data indicate that cellulose synthesis in Marchantia requires only a single protein, indicating that the heterotrimeric CESA dogma may need revision.