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- Title
Xylans Provide the Structural Driving Force for Mucilage Adhesion to the Arabidopsis Seed Coat.
- Authors
Ralet, Marie-Christine; Crépeau, Marie-Jeanne; Vigouroux, Jacqueline; Tran, Joseph; Berger, Adeline; Sallé, Christine; Granier, Fabienne; Botran, Lucy; North, Helen M.
- Abstract
Arabidopsis (Arabidopsis thaliana) seed coat epidermal cells produce large amounts of mucilage that is released upon imbibition. This mucilage is structured into two domains: an outer diffuse layer that can be easily removed by agitation and an inner layer that remains attached to the outer seed coat. Both layers are composed primarily of pectic rhamnogalacturonan I (RG-I), the inner layer also containing rays of cellulose that extend from the top of each columella. Perturbation in cellulosic ray formation has systematically been associated with a redistribution of pectic mucilage from the inner to the outer layer, in agreement with cellulose-pectin interactions, the nature of which remained unknown. Here, by analyzing the outer layer composition of a series of mutant alleles, a tight proportionality of xylose, galacturonic acid, and rhamnose was evidenced, except for mucilage modified5-1 (mum5-1; a mutant showing a redistribution of mucilage pectin from the inner adherent layer to the outer soluble one), for which the rhamnose-xylose ratio was increased drastically. Biochemical and in vitro binding assay data demonstrated that xylan chains are attached to RG-I chains and mediate the adsorption of mucilage to cellulose microfibrils. mum5-1 mucilage exhibited very weak adsorption to cellulose. MUM5 was identified as a putative xylosyl transferase recently characterized as MUCI21. Together, these findings suggest that the binding affinity of xylose ramifications on RG-I to a cellulose scaffold is one of the factors involved in the formation of the adherent mucilage layer.
- Subjects
ARABIDOPSIS thaliana; MUCILAGE; SEED coats (Botany); XYLANS; RHAMNOGALACTURONANS; MICROFIBRILS
- Publication
Plant Physiology, 2016, Vol 171, Issue 1, p165
- ISSN
0032-0889
- Publication type
Article
- DOI
10.1104/pp.16.00211