Soluble and Membrane-Bound β-Glucosidases Are Involved in Trimming the Xyloglucan Backbone. Issue 2 (12th December 2016)

• Record Type: Journal Article
• Authors: Sampedro, Javier; Valdivia, Elene R.; Fraga, Patricia; Iglesias, Natalia; Revilla, Gloria; Zarra, Ignacio
• Is Part Of: Plant physiology. Volume 173:Issue 2(2017)
• Page Start: 1017
• Page End: 1030
• Publication Date: 2016-12-12
• Subjects: Plant physiology -- Periodicals; Botany -- Periodicals; Periodicals; Electronic journals; 571.2
• DOI: 10.1104/pp.16.01713
• Languages: English
• ISSNs: 0032-0889

Abstract

Abstract : Two Arabidopsis glucosidases, soluble BGLC1 and GPI-anchored BGLC3, are involved in xyloglucan metabolism and could differentially affect wall-bound and soluble fractions. 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.