AXY8 Encodes an α-Fucosidase, Underscoring the Importance of Apoplastic Metabolism on the Fine Structure of Arabidopsis Cell Wall Polysaccharides

Abstract

An Arabidopsis thaliana mutant with an altered structure of its hemicellulose xyloglucan (XyG; axy-8) identified by a forward genetic screen facilitating oligosaccharide mass profiling was characterized. axy8 exhibits increased XyG fucosylation and the occurrence of XyG fragments not present in the wild-type plant. AXY8 was identified to encode an a-fucosidase acting on XyG that was previously designated FUC95A. Green fluorescent protein fusion localization studies and analysis of nascent XyG in microsomal preparations demonstrated that this glycosylhydrolase acts mainly on XyG in the apoplast. Detailed structural analysis of XyG in axy8 gave unique insights into the role of the fucosidase in XyG metabolism in vivo. The genetic evidence indicates that the activity of glycosylhydrolases in the apoplast plays a major role in generating the heterogeneity of XyG side chains in the wall. Furthermore, without the dominant apoplastic glycosylhydrolases, the XyG structure in the wall is mainly composed of XXXG and XXFG subunits.

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.…”

Monitoring Polysaccharide Dynamics in the Plant Cell Wall

“…So far, this promising method was used only to track the composition and distribution of arabinoxylan and mixed-linkage glucans during endosperm maturation in wheat (Triticum aestivum; Veli ckovi c et al, 2014). However, MALDI mass spectrometry can detect all major classes of cell wall polysaccharides (Westphal et al, 2010) and was used successfully to screen for Arabidopsis axy mutants with altered XyG structures (Gille et al, 2011;Günl et al, 2011aGünl et al, , 2011bGünl and Pauly, 2011;Schultink et al, 2015). Hence, MALDI when coupled with microscopy offers the possibility to (1) enhance the chemical wall structural resolution down to the cellular level and (2) image the dynamics of multiple polysaccharides in situ.…”

AUXIN BINDING PROTEIN1 Links Cell Wall Remodeling, Auxin Signaling, and Cell Expansion in Arabidopsis

“…To manipulate XyG fucosylation in ABP1 knockdown seedlings, we took advantage of previously reported plants that are either defective for the Golgi-located FUT1/MUR2 fucosyl transferase, responsible for XyG fucosylation during biosynthesis (Vanzin et al, 2002), or overexpress the apoplastic FUC95A fucosidase (35S:AXY8) promoting XyG defucosylation in muro (Günl et al, 2011). The conditional construct for ABP1 was introgressed by crossing into the mur2-1 mutant, which is null for the fucosyl transferase FUT1/MUR2 and into 35S:AXY8 transformants.…”

“…Modifications of XyGcellulose interaction or remodeling of XyG by metabolizing enzymes may modulate cell wall extensibility and thus facilitate cell expansion. Substantial experimental data support a major role of XyG in cell elongation (Cosgrove, 2005;Wolf et al, 2012), but characterization of Arabidopsis thaliana mutants altered in XyG structure or even lacking substituted XyG has raised doubts about the critical function of XyGs, as these mutants exhibit no or only subtle phenotypes when grown under standard laboratory conditions (Vanzin et al, 2002;Tamura et al, 2005;Cavalier et al, 2008;Zabotina et al, 2008;Günl et al, 2011). Plant plasticity and compensation mechanisms may account for the lack of apparent phenotypes.…”