Starting to Gel: How Arabidopsis Seed Coat Epidermal Cells Produce Specialized Secondary Cell Walls

Abstract

For more than a decade, the Arabidopsis seed coat epidermis (SCE) has been used as a model system to study the synthesis, secretion and modification of cell wall polysaccharides, particularly pectin. Our detailed re-evaluation of available biochemical data highlights that Arabidopsis seed mucilage is more than just pectin. Typical secondary wall polymers such as xylans and heteromannans are also present in mucilage. Despite their low abundance, these components appear to play essential roles in controlling mucilage properties, and should be further investigated. We also provide a comprehensive community resource by re-assessing the mucilage phenotypes of almost 20 mutants using the same conditions. We conduct an in-depth functional evaluation of all the SCE genes described in the literature and propose a revised model for mucilage production. Further investigation of SCE cells will improve our understanding of plant cell walls.

Monitoring Polysaccharide Dynamics in the Plant Cell Wall

“…1, D-G). This specialized cell wall contains more than 90% pectin and only minor amounts of cellulose and hemicellulose (Voiniciuc et al, 2015b). Thick, hydrophilic capsules of mucilage can be immunolabeled indirectly with the CCRC-M36 mAb ( Fig.…”

How does the cell wall ‘stick’ in the mucilage? A detailed microstructural analysis of the seed coat mucilaginous cell wall

“…The second type has additional cellulose fibrils and was described as cellulose mucilage characteristic of many diverse families such as Asteraceae, Brassicaceae, Lamiaceae or Plantaginaceae (Western, 2012;Kreitschitz et al, 2009;Kreitschitz, 2012). As the seed coat of Arabidopsis thaliana, a model plant, is amenable to genetic manipulation and due to the special character of its mucilage, it has been adapted to diverse studies of the functional aspects of the cell wall (Haughn and Western, 2012;North et al, 2014;Voiniciuc et al, 2015a). Although our knowledge of seed coat mucilage composition, function and development is quite extensive, the detailed structural, spatial organization of the mucilage components still remains unclear (Macquet et al, 2007;Mendu et al, 2011;Sullivan et al, 2011;Haughn and Western, 2012).…”

Xylans Provide the Structural Driving Force for Mucilage Adhesion to the Arabidopsis Seed Coat

“…Coupled with in situ immunolabeling, these techniques have enabled detailed information to be obtained about the structure and composition of the inner layer. As well as RG-I, cellulose is present together with minor amounts of galactan, arabinan, mannan, and homogalacturonan (HG; Penfield et al, 2001;Willats et al, 2001;Macquet et al, 2007a;Arsovski et al, 2009;Harpaz-Saad et al, 2011;Sullivan et al, 2011;Saez-Aguayo et al, 2013;Yu et al, 2014;Voiniciuc et al, 2015c). The majority of the methylesterified HG labeled in adherent mucilage, however, has been shown to be derived from fragments of the outer cell wall trapped in the mucilage (Saez-Aguayo et al, 2013).…”

“…This can be overcome by digestion with pectolytic and cellulolytic enzymes in admixture after removal of the outer mucilage (Macquet et al, 2007a) or by high-speed mechanical agitation (Voiniciuc et al, 2015c). Coupled with in situ immunolabeling, these techniques have enabled detailed information to be obtained about the structure and composition of the inner layer.…”