Characterization of the structure, expression and function of Pinus radiata D. Don arabinogalactan-proteins

Abstract

A synthetic phenylglycoside (beta-GlcY) that interacts specifically with arabinogalactan-proteins (AGPs), a class of plant cell surface proteoglycans, has been used to study the spatial distribution of AGPs in the xylem tissue of radiata pine. These studies demonstrated that AGPs were located in the compound middle lamella (CML) of the newly developed tracheid. Abundant, low salt extractable AGPs were purified from xylem tissue. Monosaccharide analysis showed that arabinose and galactose were the main sugars present. Linkage analysis showed that most of the arabinose was in the furanose form, at the terminal and 5-linked positions, and the majority of the galactose was in the pyranose form at the terminal 3-, 6- and 3,6-linked positions; a linkage composition typical of AGPs. The AGPs had an abundance of characteristic amino acid residues including alanine, hydroxyproline, proline, and serine. Separation of the AGPs using reversed-phase high performance liquid chromatography showed that one main fraction was eluted, which tested positive for AGPs by dot-blot analysis using anti-AGP monoclonal antibodies. Sedimentation equilibrium analysis showed that this main fraction contained a 226 kDa species. We have examined the function of AGPs in tracheid differentiation using an established radiata pine callus culture system grown on media containing beta-GlcY. The effect of beta-GlcY on the cultures was to reduce the overall tracheid differentiation rate in a concentration dependent manner, ultimately resulting in cell death. These studies provide further evidence that AGPs play an important role in tracheid differentiation, and thus may be an important biological target for improving wood quality.

Comparative genomics reveals conservative evolution of the xylem transcriptome in vascular plants

“…AGPs may act as cell wall plasticizers, enlarging the pectin matrix, and allowing wall extension and cell expansion [52]. Radiata pine AGPs are located in the compound middle lamella of newly developed tracheids [53]. Expression of AGPs containing FLA domains has recently been found to influence the mechanical strength of stems of the herbaceous ( Arabidopsis ) and woody ( Eucalyptus ) angiosperms [54].…”

Localization of Cell Wall Polysaccharides in Normal and Compression Wood of Radiata Pine: Relationships with Lignification and Microfibril Orientation

“…Arabinogalactan proteins, galacturonans, and xyloglucans are characteristic of primary cell walls in conifer xylem (Putoczki et al, 2007(Putoczki et al, , 2008Hsieh et al, 2009) while arabino-4-O-methylglucuronoxylan and O-acetyl-galactoglucomannan are the main noncellulosic polysaccharides of secondary cell walls (Melton et al, 2009). In compression wood, the amounts of xylan and mannan are reduced relative to normal wood.…”

The Cytoskeleton and Its Role in Determining Cellulose Microfibril Angle in Secondary Cell Walls of Woody Tree Species

“…Because of their location in the cell wall and the presence of a predicted glycophosphotidyl inositol (GPI) anchor domain in many AGPs, which would localise them to the outer leaflet of the plasma membrane, it was suggested that their function is to transmit information between the cell wall and cytoplasm [120]. AGPs are believed to play an important role in tracheid differentiation [121] and pharmacological and genetic studies provide strong evidence for a link between AGP and microtubules [122][123][124]. The existence of lipid rafts in the plasma membrane or a third protein or protein complex has been suggested as physical linkers between AGPs and the microtubule cortical array [123,125].…”