Natural variation in the polysaccharide components of Arabidopsis seed coat epidermal cells

National audience; During Arabidopsis seed differentiation the epidermal cells of the testa produce a variety of cell wall structures. Fully differentiated cells are characterised by reinforced proximal and radial cell walls and a central columella of secondary cell wall material, a distal primary cell wall, and mucilage polysaccharides surrounding the columella. The latter are released on imbibition to form a hydrogel that surrounds the seed. We have previously shown that Arabidopsis mucilage is formed of a mixture of polysaccharides in two structurally distinct layers, both of which are mainly composed of the pectin rhamnogalacturonan I [1]. A simple visual screen for the absence of mucilage release has allowed the identification of natural Arabidopsis variants affected in two novel loci that influence polysaccharide properties; the MUM2 beta–galactosidase and the PMEI6 pectin methylesterase [2, 3, 4]. Most Arabidopsis accessions release mucilage when imbibed and we have examined the extent of natural variability in soluble mucilage characteristics. Mucilage composition varied little between accessions; in contrast the amount and physicochemical properties of mucilage vary widely. Analyses have been carried out to link these variations with particular habitats and potential mucilage functions.