Xylans Provide the Structural Driving Force for Mucilage Adhesion to the Arabidopsis Seed Coat. Issue 1 (15th March 2016)

• Record Type: Journal Article
• Authors: Ralet, Marie-Christine; Crépeau, Marie-Jeanne; Vigouroux, Jacqueline; Tran, Joseph; Berger, Adeline; Sallé, Christine; Granier, Fabienne; Botran, Lucy; North, Helen M.
• Is Part Of: Plant physiology. Volume 171:Issue 1(2016)
• Page Start: 165
• Page End: 178
• Publication Date: 2016-03-15
• Subjects: Plant physiology -- Periodicals; Botany -- Periodicals; Periodicals; Electronic journals; 571.2
• DOI: 10.1104/pp.16.00211
• Languages: English
• ISSNs: 0032-0889

Abstract

Abstract : Arabidopsis seed mucilage contains a population of RG-I with xylan side branches that mediate the adsorption of mucilage to cellulose microfibrils in vitro. 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.