MAURA CANNON

Dissecting the role of the cell wall structural protein RSH in cell wall assembly.

The major research topic of the lab is to find out how plant cell walls assemble, and how this assembly affects cytokinesis. Plant cell walls, rather than being the uninteresting, mostly dead material they were once regarded, are now considered by a growing number of scientists to be the most ‘valuable’ part of the plant: The wall is of significant scientific value in that its assembly is fundamental to plant growth and development; it is of enormous commercial value as it provides most of the worlds food, fiber and fuel, in addition to much of the world’s medicines. The wall is an extracellular matrix with dynamic properties comprising three interpenetrating polymeric networks: cellulosic, pectic and structural glycoproteins. Cell wall mutants show that even small changes in a wall component can profoundly influence wall properties. The rsh mutant of Arabidopsis particularly exemplifies this –knockout of the RSH protein results in lethal embryos with an aberrant cell plate and abnormally shaped cells. Significantly, this demonstrates that the RSH protein, an extensin type of hydroxyproline-rich glycoprotein (HRGP), is essential for the correct assembly and orientation of the cross-wall required for cytokinesis during embryogenesis. Therefore, the rsh mutant provides a direct route to the further functional analysis of these intriguing structural glycoproteins involved in multifarious biological roles but currently lacking precise molecular detail. The essential requirement of RSH extensin for cytokinesis raises several questions. To start out I would like to find out what properties of RSH determine its role in wall assembly. To this end I have been asking: what is the best strategy for the functional analysis of RSH at the molecular level? The scheme I have come up with is very exciting and can be broken down into several projects tailored to the student’s background, interests and time constraints.

The mature RSH has 404 amino acids, and being a typical extensin type structural protein, is rich in Ser, Pro, Lys, Val, His and Tyr. These residues are arranged in major repetitive modules that contain sub-motifs, as is usual for structural proteins. The plan is to dissect RSH motif-by-motif by constructing RSH analogs, and to test functionality by their ability to rescue the rsh mutant. Students projects will be: to construct specific analogs of RSH, transform the rsh mutant, and analyze the progeny phenotype. This approach integrates cell wall biology and biochemistry with methods ranging from protein design and characterization to molecular genetics to cell biology.