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Research article - Peer-reviewed, 2020

Golgi-localized exo-beta 1,3-galactosidases involved in cell expansion and root growth in Arabidopsis

Nibbering, Pieter; Petersen, Bent L.; Motawia, Mohammed Saddik; Jorgensen, Bodil; Ulvskov, Peter; Niittyla, Totte

Abstract

Plant arabinogalactan proteins (AGPs) are a diverse group of cell surface- and wall-associated glycoproteins. Functionally important AGP glycans are synthesized in the Golgi apparatus, but the relationships among their glycosylation levels, processing, and functionalities are poorly understood. Here, we report the identification and functional characterization of two Golgi-localized exo-beta-1,3-galactosidases from the glycosyl hydrolase 43 (GH43) family inArabidopsis thaliana. GH43 loss-of-function mutants exhibited root cell expansion defects in sugar-containing growth media. This root phenotype was associated with an increase in the extent of AGP cell wall association, as demonstrated by Yariv phenylglycoside dye quantification and comprehensive microarray polymer profiling of sequentially extracted cell walls. Characterization of recombinant GH43 variants revealed that the exo-beta-1,3-galactosidase activity of GH43 enzymes is hindered by beta-1,6 branches on beta-1,3-galactans. In line with this steric hindrance, the recombinant GH43 variants did not release galactose from cell wall-extracted glycoproteins or AGP-rich gum arabic. These results indicate that the lack of exo-beta-1,3-galactosidase activity alters cell wall extensibility in roots, a phenotype that could be explained by the involvement of galactosidases in AGP glycan biosynthesis.

Keywords

glycoside hydrolase 43; Golgi; glycosylation; arabinogalactan proteins; Arabidopsis; roots; cell expansion; plant cell wall; exo-beta 13-galactosidase; comprehensive microarray polymer profiling (CoMPP) microarray; cell wall; Arabidopsis thaliana; glycoside hydrolase; glycosidase; glycoprotein biosynthesis; arabinogalactan protein; exo-beta 1; 3-galactosidase

Published in

Journal of Biological Chemistry
2020, Volume: 295, number: 31, pages: 10581-10592
Publisher: AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC