AtBGAL10 Is the Main Xyloglucan β-Galactosidase in Arabidopsis, and Its Absence Results in Unusual Xyloglucan Subunits and Growth Defects    

Abstract

In growing cells, xyloglucan is thought to connect cellulose microfibrils and regulate their separation during wall extension. In Arabidopsis (Arabidopsis thaliana), a significant proportion of xyloglucan side chains contain b-galactose linked to a-xylose at O2. In this work, we identified AtBGAL10 (At5g63810) as the gene responsible for the majority of b-galactosidase activity against xyloglucan. Xyloglucan from bgal10 insertional mutants was found to contain a large proportion of unusual subunits, such as GLG and GLLG. These subunits were not detected in a bgal10 xyl1 double mutant, deficient in both b-galactosidase and a-xylosidase. Xyloglucan from bgal10 xyl1 plants was enriched instead in XXLG/XLXG and XLLG subunits. In both cases, changes in xyloglucan composition were larger in the endoglucanase-accessible fraction. These results suggest that glycosidases acting on nonreducing ends digest large amounts of xyloglucan in wild-type plants, while plants deficient in any of these activities accumulate partly digested subunits. In both bgal10 and bgal10 xyl1, siliques and sepals were shorter, a phenotype that could be explained by an excess of nonreducing ends leading to a reinforced xyloglucan network. Additionally, AtBGAL10 expression was examined with a promoter-reporter construct. Expression was high in many cell types undergoing wall extension or remodeling, such as young stems, abscission zones, or developing vasculature, showing good correlation with a-xylosidase expression.

Group III-AXTHGenes of Arabidopsis Encode Predominant Xyloglucan Endohydrolases That Are Dispensable for Normal Growth

“…However, these results do not support XEHs as major actors in controlling cell wall extension. The XEHs encoded by AtXTH31 and AtXTH32 may instead be the key enzymes in a xyloglucan-recycling pathway composed of recently discovered Arabidopsis a-L-fucosidases, b-galactosidases, a-xylosidases, b-glucosidases, and their homologs, which are similarly up-regulated in cells undergoing wall extension and/or remodeling (Iglesias et al, 2006;Sampedro et al, 2010Sampedro et al, , 2012Günl et al, 2011). In light of our current work and these recent analyses, continued scrutiny of the role of polysaccharide hydrolases in the context of cell wall morphogenesis is clearly warranted.…”

Xyloglucan Metabolism Differentially Impacts the Cell Wall Characteristics of the Endosperm and Embryo during Arabidopsis Seed Germination

“…In addition to XYL1, two other glycosidases, BGAL10 and AXY8, have been characterized that trim Gal and Fuc, respectively, off XyG side chains Sampedro et al, 2012). To determine whether mutations of BGAL10 and AXY8 affect germination characteristics, we assessed dormancy, sensitivity to paclobutrazol, and thermoinhibition at 34°C of two T-DNA insertion alleles (bgal10-1 and bgal10-2; Sampedro et al, 2012), two EMS (axy8-1 and axy8-2), and two T-DNA insertion alleles (axy8-5 and axy8-6; .…”

“…The XyG-deficient double mutant xxt1 xxt2 shows no major growth defect except for deformed root hairs . Nevertheless, it was recently reported that the production of Gal-depleted XyG causes dwarfism in the galactosyltransferase mutant mur3 (Kong et al, 2015) in contrast to xyl1 and bgal10, where increased galactosylation results in shorter but wider siliques Sampedro et al, 2012). Phenotypes have not been observed from either reduced or increased fucosylation in the fucosyltransferase mutant mur2 and fucosidase mutant axy8 (Vanzin et al, 2002;.…”

“…Subsequent trimming of XyG chains is performed by apoplastic glycosidases and determines hemicellulose structure and properties in the wall (Scheller and Ulvskov, 2010). A number of genes involved in the XyG metabolism have been identified, including XYL1, BGAL10, and AXY8 encoding, respectively, a-xylosidase, b-galactosidase, and a-fucosidase Sampedro et al, 2012). Loss of function of these glycosidases results in significant alterations in XyG composition.…”

XTH31, Encoding an in Vitro XEH/XET-Active Enzyme, Regulates Aluminum Sensitivity by Modulating in Vivo XET Action, Cell Wall Xyloglucan Content, and Aluminum Binding Capacity in Arabidopsis

“…In the standard nomenclature for xyloglucan structures, unsubstituted Glc residues are represented by G, while X, L, and F indicate Glc residues that are 6-O-substituted with a-D-Xylp, b-D-Galp-(1-2)-a-D-Xylp, and a-L-Fucp-(1-2)-b-D-Galp-(1-2)-a-D-Xylp side chains, respectively . Treatment of Arabidopsis xyloglucan with an endoglucanase (XEG) that attacks unsubstituted Glc residues yields an oligosaccharide mixture that includes XXXG, XXLG, XLXG, XXG, GXXG, XLLG, XXFG, and XLFG (the sequences are shown with the reducing end of the molecule positioned to the right; Madson et al, 2003;Obel et al, 2009;Sampedro et al, 2012).…”