An Arabidopsis Cell Wall Proteoglycan Consists of Pectin and Arabinoxylan Covalently Linked to an Arabinogalactan Protein

Abstract

Plant cell walls are comprised largely of the polysaccharides cellulose, hemicellulose, and pectin, along with ;10% protein and up to 40% lignin. These wall polymers interact covalently and noncovalently to form the functional cell wall. Characterized cross-links in the wall include covalent linkages between wall glycoprotein extensins between rhamnogalacturonan II monomer domains and between polysaccharides and lignin phenolic residues. Here, we show that two isoforms of a purified Arabidopsis thaliana arabinogalactan protein (AGP) encoded by hydroxyproline-rich glycoprotein family protein gene At3g45230 are covalently attached to wall matrix hemicellulosic and pectic polysaccharides, with rhamnogalacturonan I (RG I)/homogalacturonan linked to the rhamnosyl residue in the arabinogalactan (AG) of the AGP and with arabinoxylan attached to either a rhamnosyl residue in the RG I domain or directly to an arabinosyl residue in the AG glycan domain. The existence of this wall structure, named ARABINOXYLAN PECTIN ARABINOGALACTAN PROTEIN1 (APAP1), is contrary to prevailing cell wall models that depict separate protein, pectin, and hemicellulose polysaccharide networks. The modified sugar composition and increased extractability of pectin and xylan immunoreactive epitopes in apap1 mutant aerial biomass support a role for the APAP1 proteoglycan in plant wall architecture and function.

SALT-OVERLY SENSITIVE5 Mediates Arabidopsis Seed Coat Mucilage Adherence and Organization through Pectins

“…AGPs have also been shown to bind specifically to pectins in a calcium-dependent manner (Baldwin et al, 1993). Most recently, an AGP has been shown to be covalently linked to rhamnosyl residues of RG I and an arabinoxylan polysaccharide (Tan et al, 2013). This linkage suggests that noncellulosic carbohydrates in the cell wall form extensive networks that contribute to cell wall strength (Tan et al, 2013).…”

“…The GPI anchor can also be cleaved, releasing the AGPs from the membrane into the cell wall (Schultz et al, 2000). Although their exact roles are still unclear, AGPs have been proposed to interact with cell wall polysaccharides, initiate intracellular signaling cascades, and influence a wide variety of biological processes (for review, see Seifert and Roberts, 2007;Ellis et al, 2010;Tan et al, 2013).…”

Abscisic Acid- and Stress-Induced Highly Proline-Rich Glycoproteins Regulate Root Growth in Rice

“…Some RePRPs are localized to the plasma membrane, where they interact with the polysaccharide AG in the walls, which is produced when plant cells are wounded or under stress, leading to the repression of cell elongation. Alternatively, RePRPs could exert their regulatory role on the function of cell walls by binding to the AG moiety of plasma membrane-localized AGP, which has recently been shown to be linked to cell wall polysaccharides arabinoxylan and pectin (Tan et al, 2013). Proper O-glycosylation of RePRPs could be important for its function, similar to the role of O-glycosylation on HRGP regulation of root hair development (Velasquez et al, 2011).…”

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…Plant biomass components do not accumulate independently of each other, though their relationships are still an active area of research (Dick-Perez et al, 2011;Tan et al, 2013;Mikkelsen et al, 2015). Biomass component amounts can correlate because they are physically bound to each other through covalent and non-covalent bonds or because they accumulate in the same plant organ or stage of plant development, though a physical interaction may not exist.…”