Biosynthesis, Localisation, and Function of Pectins in Plants
Pectins constitute a group of charged matrix polysaccharides, which are made by plants and are applied across a wide range of industries. Pectins are deeply conserved wall components in plants and constitute a group of charged matrix polysaccharides. They
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Biosynthesis, Localisation, and Function of Pectins in Plants Yang Yang and Charles T. Anderson
1.1 Pectin Biosynthesis Pectins are a class of matrix polysaccharides in the cell wall that contains three major domains: homogalacturonan (HG), rhamnogalacturonan I (RG-I), and rhamnogalacturonan II (RG-II) (see Chap. 2). Galacturonic acid (GalA) monomers form the backbones of HG and RG-II domains, whereas rhamnose-GalA dimers form the backbone of RG-I. Both types of RG can be linked to HG, and HG and RG-I can also be covalently attached to an arabinogalactan protein (Fig. 1.1) (Atmodjo et al. 2013; Tan et al. 2013). Pectic polysaccharides are synthesised in the Golgi apparatus, with related glycoproteins simultaneously synthesised in different Golgi cisternae (Moore et al. 1991) (Fig. 1.1). Newly synthesised pectins are packaged into vesicles and delivered to the cell wall (Moore et al. 1991). Approximately 67 transferases, including glycosyltransferases, methyltransferases, and acetyltransferases, are predicted to function in pectin biosynthesis. Glycosyltransferases function in synthesising pectin backbones and adding side chains, whereas methyltransferases and acetyltransferases catalyse pectin methyl-esterification and acetylation, respectively (Mohnen 2008). In addition, the synthesis and correct localisation of nucleotide sugars, which are the substrates for pectin synthesis, require the action of other enzymes, including interconversion enzymes, sugar kinases, UDP-sugar pyrophosphorylases, and nucleotide sugar transporters (Atmodjo et al. 2013). HG, the most abundant domain of pectins, is a linear polymer of galacturonic acid (GalA), and is partially modified with methyl groups and acetyl groups at the Y. Yang Laboratory of Cell and Molecular Biology, Institute of Vegetable Science, Zhejiang University, Hangzhou, China C. T. Anderson (*) Department of Biology, The Pennsylvania State University, University Park, PA, USA e-mail: [email protected] © Springer Nature Switzerland AG 2020 V. Kontogiorgos (ed.), Pectin: Technological and Physiological Properties, https://doi.org/10.1007/978-3-030-53421-9_1
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Y. Yang and C. T. Anderson
Fig. 1.1 Pectin synthesis and domain arrangement. Pectins are synthesised in the Golgi apparatus and secreted to the cell wall. The inset box shows current hypotheses about pectin synthesis: in the consecutive glycosyltransferase model, UDP-GalA or UDP-Rha are consecutively added to the non-reducing end of pectin chains by glycosyltransferases; in the domain synthesis model, pectin domains are elongated separately by glycosyltransferases, then linked with other domains. In the cell wall, pectin domains are arranged in at least three different covalently linked configurations. Figure made with BioRender
C-6 and O-2/O-3 positions, respectively. Galacturonosyltransferases (GAUTs) transfer UDP-GalA onto the non-reducing end of oligogalacturonide, resulting in HG chain elongation (Scheller et al. 1999). In Arabidopsis thaliana, the GAUT and GAUT-LIKE gene families contain 15 and 10 gene
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