Grant: Discovery Grants Program - Individual

During differentiation of the Arabidopsis seed coat epidermis, a large amount of mucilage, comprised primarily of pectin, is produced and secreted from the cells. Subsequently an extensive secondary cell wall is synthesized. Upon exposure of mature seed to water, the mucilage expands to envelop the seed providing protection and moisture prior to germination. Unlike many specialized cell types the seed coat epidermis is not essential for viability, allowing for the isolation of mutants defective in various aspects of its differentiation. Thus, the Arabidopsis seed coat represents an excellent model system for genetic dissection of cell wall biogenesis, especially with respect to pectin. We have been using this system to identify and clone genes encoding proteins needed for mucilage structure and function. Three of these genes, MUM1, MUM2 and FLY are all required for proper mucilage extrusion from the seed coat when exposed to water. We believe that investigating the role of these genes will contribute to understanding how plants modulate pectin to produce different physical properties required during growth and development. Our recent cloning of the MUM2 gene indicates that it encodes a hydrolytic enzyme that modifies the mucilage outside the cell following secretion and may be analogous to processes involved in fruit ripening. MUM1 encodes a transcription factor that may control mucilage extrusion by regulating genes like MUM2 needed to modify mucilage structure. We are close to cloning the FLY gene. We propose here to 1) continue our analysis of the role of all three of the genes and their protein products, 2) study the biochemical structure of the seed coat mucilage in more detail and 3) isolate and characterize a new generation of seed coat mutants. Upon completion of this work we hope to better understand pectin structure and how it can be modified to alter its physical properties. This work should generate information and tools needed to manipulate pectin structure and function in vivo.