Binding of Arabinogalactan Proteins by Yariv Phenylglycoside Triggers Wound-Like Responses in Arabidopsis Cell Cultures  

Abstract

Arabinogalactan-proteins (AGPs) are cell wall proteoglycans and are widely distributed in the plant kingdom. Classical AGPs and some nonclassical AGPs are predicted to have a glycosylphosphatidylinositol lipid anchor and have been suggested to be involved in cell-cell signaling. Yariv phenylglycoside is a synthetic probe that specifically binds to plant AGPs and has been used to study AGP functions. We treated Arabidopsis suspension cell cultures with Yariv phenylglycoside and observed decreased cell viability, increased cell wall apposition and cytoplasmic vesiculation, and induction of callose deposition. The induction of cell wall apposition and callose synthesis led us to hypothesize that Yariv binding of plant surface AGPs triggers wound-like responses. To study the effect of Yariv binding to plant surface AGPs and to further understand AGP functions, an Arabidopsis whole genome array was used to monitor the transcriptional modifications after Yariv treatment. By comparing the genes that are induced by Yariv treatment with genes whose expressions have been previously shown to be induced by other conditions, we conclude that the gene expression profile induced by Yariv phenylglycoside treatment is most similar to that of wound induction. It remains uncertain whether the Yariv phenylglycoside cross-linking of cell surface AGPs induces these genes through a specific AGP-based signaling mechanism or through a general mechanical perturbation of the cell surface.Arabinogalactan-proteins (AGPs) are widely distributed in plant species and are located at the plasma membrane and cell wall and in the media of cell cultures. These proteoglycans are typically composed of at least 90% carbohydrate by weight. The AGP core polypeptide is usually rich in Hyp, Ser, Thr, and Ala. Extended motifs comparable to those of extensins are not generally found in AGPs, although short stretches of Hyp alternating with Ala or Ser occur in many AGPs. The sugar moieties are composed of (1/3)-b-D-galactan backbones and (1/6)-b-D-galactan side chains with terminal sugars of Ara or GlcUA (Nothnagel, 1997). In the classical AGPs, the nascent polypeptide chain is synthesized with a C-terminal hydrophobic sequence that is later replaced with a glycosylphosphatidylinositol lipid anchor in the mature protein (Gaspar et al., 2001). The Arabidopsis genome contains approximately 47 genes encoding AGP core polypeptides (Schultz et al., 2002).The abundance of AGP genes and the high degree of posttranslational modifications of AGPs suggest a high genome investment in the synthesis of AGPs, which indicates that these macromolecules have conserved and important roles in plants. Although several possible roles of AGPs have been suggested (MajewskaSawka and Nothnagel, 2000), the detailed biological functions of AGPs currently remain unknown. Many experiments have demonstrated that the expression of AGPs is developmentally regulated in tissueand organ-specific manners (Majewska-Sawka and Nothnagel, 2000). Other experiments showed that AGPs are involved in s...

Glycosylphosphatidylinositol-Anchored Proteins Are Required for Cell Wall Synthesis and Morphogenesis in Arabidopsis

“…This uncontrolled wall deposition, coupled with a decrease in cellulose, likely compromises the mechanical integrity of the wall and could therefore trigger callose synthesis as part of a stress or wound response. A second, nonexclusive explanation for the accumulation of callose in the mutants is suggested by the experiments showing that treatment of Arabidopsis cell cultures with Yariv reagent induces callose production and programmed cell death (Gao and Showalter, 1999;Guan and Nothnagel, 2004). These experiments with Yariv reagent also suggest that a lack of AGPs in pnt1 embryos and cells might be responsible for the seedling lethality of pnt1 and necrosis seen in pnt1 callus.…”

Plant O-Hydroxyproline Arabinogalactans Are Composed of Repeating Trigalactosyl Subunits with Short Bifurcated Side Chains

“…Nevertheless, despite considerable speculation (4,36), specific biological roles of classical AGPs and their Hyp-AGs remain to be elucidated. The ubiquity of AGPs at the cell surface and involvement of classical AGPs in numerous fundamental developmental processes is clear (3,(37)(38)(39)(40)(41)), yet AGP function at molecular levels is relatively unexplored. The current structural elucidation including computer simulations support structural roles for classical AGPs as follows.…”

Interactions between MUR10/CesA7-Dependent Secondary Cellulose Biosynthesis and Primary Cell Wall Structure

“…Mutations in the AtXTH27 gene, coding for a cell wall-remodeling enzyme, cause a lesion-mimic phenotype (Matsui et al, 2005). RNA interference with pectin biosynthesis, pharmacological interference with cellulose biosynthesis, and AGP damage in suspension cell function all triggered programmed cell death (Guan and Nothnagel, 2004;Duval et al, 2005;Ahn et al, 2006). The above examples indicate that defective primary cell walls affect signaling events leading to local and systemic stress responses.…”