Changing spaces: the Arabidopsis mucilage secretory cells as a novel system to dissect cell wall production in differentiating cells1

As the outer boundary of plant cells, the cell wall is integral to all aspects of plant growth, development, and interactions with the environment. Dicot primary cell walls are composed of a network of cellulose, hemicellulose and proteins embedded in a matrix of acidic pectins. Pectins are synthesized in the Golgi apparatus by the sequential addition of nucleotide sugars by glycosyltransferases, following which they are secreted to the apoplast. During their differentiation, the mucilage secretory cells (MSCs) of the Arabidopsis seed coat undergo sequential biosynthesis and secretion of a primarily pectinaceous mucilage followed by secondary cell wall production. Several genes affecting MSC differentiation have been identified with roles ranging from the production of nucleotide sugar substrates for pectin synthesis to putative cell wall modification enzymes to transcription factors required to control MSC differentiation. These preliminary studies of the MSCs demonstrate that they will play a valuable role in gene discovery related to cell wall production and modification. Furthermore, they have the potential to become an important system in which to study the interaction and regulation of pectin biosynthetic factors in differentiating cells. These results will contribute to answering the important question of how cell wall production and modification occur throughout a growing plant living in a complex environment.