title: Soluble and Membrane-Bound β-Glucosidases Are Involved in Trimming the Xyloglucan Backbone.
abstract: In many flowering plants, xyloglucan is a major component of primary cell walls, where it plays an important role in growth regulation. Xyloglucan can be degraded by a suite of exoglycosidases that remove specific sugars. In this work, we show that the xyloglucan backbone, formed by (1→4)-linked β-d-glucopyranosyl residues, can be attacked by two different Arabidopsis (Arabidopsis thaliana) β-glucosidases from glycoside hydrolase family 3. While BGLC1 (At5g20950; for β-glucosidase active against xyloglucan 1) is responsible for all or most of the soluble activity, BGLC3 (At5g04885) is usually a membrane-anchored protein. Mutations in these two genes, whether on their own or combined with mutations in other exoglycosidase genes, resulted in the accumulation of partially digested xyloglucan subunits, such as GXXG, GXLG, or GXFG. While a mutation in BGLC1 had significant effects on its own, lack of BGLC3 had only minor effects. On the other hand, double bglc1 bglc3 mutants revealed a synergistic interaction that supports a role for membrane-bound BGLC3 in xyloglucan metabolism. In addition, bglc1 bglc3 was complemented by overexpression of either BGLC1 or BGLC3 In overexpression lines, BGLC3 activity was concentrated in a microsome-enriched fraction but also was present in soluble form. Finally, both genes were generally expressed in the same cell types, although, in some cases, BGLC3 was expressed at earlier stages than BGLC1 We propose that functional specialization could explain the separate localization of both enzymes, as a membrane-bound β-glucosidase could specifically digest soluble xyloglucan without affecting the wall-bound polymer.
authors.affiliation: Departemento Biología Funcional, Facultad de Biología, Universidad de Santiago, Santiago de Compostela, 15782 Spain.
authors.forename: Javier
authors.identifier: 0000-0002-6534-5347
authors.initials: J
authors.lastname: Sampedro
authors.affiliation: Departemento Biología Funcional, Facultad de Biología, Universidad de Santiago, Santiago de Compostela, 15782 Spain.
authors.forename: Elene R
authors.identifier: 0000-0001-6773-0583
authors.initials: ER
authors.lastname: Valdivia
authors.affiliation: Departemento Biología Funcional, Facultad de Biología, Universidad de Santiago, Santiago de Compostela, 15782 Spain.
authors.forename: Patricia
authors.initials: P
authors.lastname: Fraga
authors.affiliation: Departemento Biología Funcional, Facultad de Biología, Universidad de Santiago, Santiago de Compostela, 15782 Spain.
authors.forename: Natalia
authors.identifier: 0000-0001-9053-4134
authors.initials: N
authors.lastname: Iglesias
authors.affiliation: Departemento Biología Funcional, Facultad de Biología, Universidad de Santiago, Santiago de Compostela, 15782 Spain.
authors.forename: Gloria
authors.identifier: 0000-0002-2150-8538
authors.initials: G
authors.lastname: Revilla
authors.affiliation: Departemento Biología Funcional, Facultad de Biología, Universidad de Santiago, Santiago de Compostela, 15782 Spain ignacio.zarra@usc.es.
authors.forename: Ignacio
authors.identifier: 0000-0001-7203-0688
authors.initials: I
authors.lastname: Zarra
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology*; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D005936:Glucans / Q000378:metabolism*; D005966:Glucuronidase / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D012995:Solubility; D014990:Xylans / Q000378:metabolism*; D005644:alpha-L-Fucosidase / Q000378:metabolism; D001617:beta-Glucosidase / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D005936:Glucans; D014990:Xylans; C029353:xyloglucan; C000622992:BGLC1 protein, Arabidopsis; C000622993:BGLC3 protein, Arabidopsis; D001617:beta-Glucosidase; D005966:Glucuronidase; D005644:alpha-L-Fucosidase