Identification of Key Enzymes for Pectin Synthesis in Seed Mucilage

Abstract

Pectin is a vital component of the plant cell wall and provides the molecular glue that maintains cell-cell adhesion, among other functions. As the most complex wall polysaccharide, pectin is composed of several covalently linked domains, such as homogalacturonan (HG) and rhamnogalacturonan I (RG I). Pectin has widespread uses in the food industry and has emerging biomedical applications, but its synthesis remains poorly understood. For instance, the enzymes that catalyze RG I elongation remain unknown. Recently, a coexpression- and sequence-based () reverse genetic screen uncovered hemicellulose biosynthetic enzymes in the Arabidopsis () seed coat. Here, we use an extension of this strategy to identify as the founding member of a glycosyltransferase family essential for the accumulation of seed mucilage, a gelatinous wall rich in unbranched RG I. Detailed biochemical and histological characterization of two mutants and two () mutants identified MUCI70 and GAUT11 as required for two distinct RG I domains in seed mucilage. We demonstrate that, unlike MUCI70, GAUT11 catalyzes HG elongation in vitro and, thus, likely is required for the synthesis of an HG region important for RG I elongation. Analysis of a double mutant confirmed that MUCI70 and GAUT11 are indispensable for the production and release of the bulk of mucilage RG I and for shaping the surface morphology of seeds. In addition, we uncover relationships between pectin and hemicelluloses and show that xylan is essential for the elongation of at least one RG I domain.

Mutations in the Pectin Methyltransferase QUASIMODO2 Influence Cellulose Biosynthesis and Wall Integrity in Arabidopsis

“…In grass and woody dicot plants, GAUT4 possesses HG:GalA transferase activity, and knockdown of GAUT4 expression promotes plant growth and enhances biomass degradability (Biswal et al, 2018). GAUT11, another confirmed HG α-1,4 GalA transferase, catalyzes HG elongation and likely functions in RG-I production in seed mucilage (Voiniciuc et al, 2018). QUASIMODO1 (QUA1/GAUT8) encodes a putative glycosyltransferase and is likely required for HG biosynthesis, since qua1 mutant plants have reduced uronic acid content in their walls and display cell adhesion defects (Bouton et al, 2002;Orfila et al, 2005;Durand et al, 2009;Verger et al, 2018).…”

Characterization of Seed, Oil, and Fatty Acid Methyl Esters of an Ethyl Methanesulfonate Mutant of Camelina sativa with Reduced Seed‐Coat Mucilage

“…Plant cell walls consist of three predominant polysaccharide carbohydrates: cellulose, hemicellulose, and pectin, which along with cellulose‐hemicellulose networks provide tensile strength (Arsovski et al, ). Pectin supports cell wall integrity by covalently linking to the tensile polysaccharides and by providing cell‐to‐cell adhesion (Voiniciuc et al, , b). The principal pectin in Arabidopsis thaliana primary cell walls is homogalacturonan (HG) (Voiniciuc et al, , b).…”

“…Pectin supports cell wall integrity by covalently linking to the tensile polysaccharides and by providing cell‐to‐cell adhesion (Voiniciuc et al, , b). The principal pectin in Arabidopsis thaliana primary cell walls is homogalacturonan (HG) (Voiniciuc et al, , b). The three major pectic structures are branched rhamnogalacturonan I (RGI) and rhamnogalacturonan II (RGII), and nonbranched HG.…”

Association Genetics and Local Adaptation of Populus trichocarpa Torr. & Gray

“…Functional characterization of one of the genes highlighted by this analysis was Potri.004G111000, identified from the multitrait GWAS for LA-LD-LL-LW. GAUT9 belongs to the GAUT gene family of proven and putative pectin homogalacturonan (HG) galacturnosyltransferases (Atmodjo et al, 2011;Sterling et al, 2006;Voiniciuc et al, 2018). Multiple lines of evidence showed that this gene can affect leaf development.…”

“…galacturnosyltransferases (Sterling et al, 2006;Atmodjo et al, 2013;Biswal et al, 2018b;Voiniciuc et al, 2018). Down-regulation of the PdGAUT9.1 gene caused increased leaf length and width in both developing and mature leaves of greenhouse-grown P. deltoides, confirming the role of the gene in leaf development in Populus.…”