Abstract
The Golgi apparatus of eukaryotic cells is known for its central role in the processing, sorting, and transport of proteins to intra- and extra-cellular compartments. In plants, it has the additional task of assembling and exporting the non-cellulosic polysaccharides of the cell wall matrix including pectin and hemicelluloses, which are important for plant development and protection. In this review, we focus on the biosynthesis of complex polysaccharides of the primary cell wall of eudicotyledonous plants. We present and discuss the compartmental organization of the Golgi stacks with regards to complex polysaccharide assembly and secretion using immuno-electron microscopy and specific antibodies recognizing various sugar epitopes. We also discuss the significance of the recently identified Golgi-localized glycosyltransferases responsible for the biosynthesis of xyloglucan (XyG) and pectin.
Highlights
One of the most important functional properties of the plant Golgi apparatus is its ability to synthesize complex matrix polysaccharides of the cell wall
Immunogold localization of these green fluorescent protein (GFP)-tagged glycosyltransferases has demonstrated that AtXT1–GFP is mainly located in the cis and medial cisternae, AtMUR3–GFP is predominantly associated with medial cisternae and AtFUT1–GFP mostly detected over trans cisternae suggesting that initiation of XyG side chains occurs in early Golgi compartments in tobacco suspension-cultured (BY-2) cells
The Arabidopsis mutant quasimodo1 is characterized by a reduced cell adhesion phenotype combined with a 25% decrease in cell wall galacturonic acid content, supporting the hypothesis that the AtQUA1 gene encodes a putative glycosyltransferase activity involved in pectin biosynthesis (Bouton et al, 2002; Durand et al, 2009)
Summary
One of the most important functional properties of the plant Golgi apparatus is its ability to synthesize complex matrix polysaccharides of the cell wall. Side chains of RG-I can contain α-l-fucosyl, β-d-glucuronosyl, and 4-Omethyl β-d-glucuronosyl residues and vary in length depending on the plant source (O’Neill et al, 1990) These chains are believed to decrease the ability of pectic molecules to cross-link and form a stable gel network, and are thereby able to influence the mechanical properties of the cell wall (Hwang and Kokini, 1991). GAX is known to be synthesized within Golgi stacks and significant advances have recently been made in understanding its biosynthesis (Faik, 2010) This is beyond the focus of this review and only major polysaccharides of the primary cell walls of eudicotyledonous are considered here below
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