The seed coat is a specialized tissue derived from ovule integuments. In some species, including Arabidopsis thaliana, large quantities of polysaccharide mucilage (pectin) and secondary cell wall are produced by seed coat epidermal cells at specific times during differentiation. Because these modifications are not required for viability, the Arabidopsis seed coat epidermal cells represent a unique dispensable tissue that can be used to identify genes involved in complex polysaccharide biosynthesis and secretion (Haughn and Chaudhury, 2005; Arsovski et al., 2010; Haughn and Western, 2012), important processes about which relatively little is known. As a first step to develop this unique model system we investigated the structure and differentiation of Arabidopsis seed coat secretory cells including the synthesis, secretion and extrusion of mucilage (Western et al., 2000) and isolated a number of mutants defective in the differentiation, synthesis and extrusion of mucilage (Western et al., 2001). Our characterization of these and other mutants and cloning of the mutated genes has identified a number of proteins playing key roles in cell wall biology including biosynthesis (MUM4; Western et al., 2004) modification (MUM2, BXL1, FLY1; Dean et al., 2007, Arsovski et al., 2009, Voiniciuc et al., 2013) secretion (Young et al., 2008; McFarlane et al., 2013) and regulation (Western et al., 2004; Huang et al., 2011) of mucilage pectins and synthesis of cellulose in mucilage (CESA5; Mendu et al., 2011) and for the the secondary cell wall columella (CESA2, CESA5, CESA9; Stork et al., 2009, Mendu et al., 2011). We have also developed some useful information and tools for the study of the seed coat including a microarray analysis (Dean et al., 2011; http://bar.utoronto.ca/efp_seedcoat/cgi-bin/efpWeb.cgi) and a seed coat specific promoter (Esfandiari et al., 2013). Finally, we have discovered a metabolic link between the production of mucilage and the synthesis of storage oil in the embryo (Shi et al., 2012) Current projects include identification of additional seed coat specific promoters, genetic modifier analysis of MUM2, investigation of mechanisms controlling secretion expression, proteomic analysis of mucilage and the engineering of cell wall carbohydrates in the mucilage pocket.