Regulation of seed coat mucilage production and modification in Arabidopsis

The Arabidopsis seed coat mucilage is a polysaccharide-rich matrix synthesized by the seed coat epidermal cells. It is a specialized cell wall mainly composed of three types of polysaccharides (i. e. pectin, hemicellulose, and cellulose), and represents as an ideal model system for plant cell wall research. A large number of genes responsible for the synthesis and modification of cell wall polysaccharides have been identified using this model system. Moreover, a subset of regulators controlling mucilage production and modification have been characterized, and the underlying transcriptional regulatory mechanisms have been elucidated. This substantially contributes to the understanding of the molecular mechanisms underlying mucilage synthesis and modification. In this review, we concisely summarize the various genes and regulators involved in seed coat cell differentiation, mucilage biosynthesis and modification, and secondary cell wall formation. In particular, we put emphasis on the latest knowledge gained regarding the transcriptional regulation of mucilage production, which is composed of a hierarchal cascade with three-layer transcriptional regulators. Collectively, we propose an updated schematic framework of the genetic regulatory network controlling mucilage production and modification in the Arabidopsis mucilage secretory cells.