CS-26-2 - CSLD Proteins Are beta-1,4-glucan Synthases That Function During Polarized Cell Wall Deposition in Arabidopsis

In plants, changes in cell morphology that occur during growth and development require the deposition of new cell wall components. Cellulose microfibrils, the major load bearing components in plant cell walls, are deposited along one or more entire faces of a cell during diffuse growth. However, during a distinct mode of focused cell expansion called tip growth, newly synthesized cell wall polysaccharides are deposited in a restricted region of the cell.  Members of the Cellulose Synthase-Like D (CSLD) family of proteins have been shown to play crucial roles during tip-restricted cell expansion in root hairs and pollen tubes, and more recently, during the construction of newly-forming cell plates in dividing cells.  Arabidopsis contains five expressed CSLD genes, with CSLD1 and CSLD4 required for tip-restricted pollen tube elongation, CSLD2 and CSLD3 required for root hair tip-growth, and CSLD5 along with CLSD2 and CSLD3 required for cell plate formation during plant cytokinesis.  While CSLD2 and CSLD3 both participate in cell plate formation, CSLD5 plays a unique role, accumulating only in dividing cells due to cell-cycle dependent protein turnover.  In tip-growing root hair cells, fluorescently-tagged CSLD3 proteins localize to an apical plasma membrane domains at the tips of growing root hairs where they synthesize beta-1,4-glucan polysaccharides required for this specialized form of cell wall deposition. We now present recent results using a combination of genetic rescue techniques, live-cell imaging, and biochemical reconstitution experiments aimed at clarifying whether CSLD2 and CSLD5 also display beta-1,4-glucan synthase activity, and examining to what degree the activities of these proteins are able to replace one another and rescue growth and developmental defects associated with csld2, csld3, and csld5 mutant phenotypes.

Coauthors: Gwangbae Bak – University of Michigan;Willian Barnes – Complex Carbohydrate Research Center, University of Georgia - Athens;Maria Pena – Complex Carbohydrate Research Center, University of Georgia - Athens;Breeanna Urbanowicz – Complex Carbohydrate Research Center, University of Georgia - Athens;Jiyuan Yang – University of Michigan