Cell Surfaces in Plant-Microorganism Interactions

Abstract

Infection of muskmelon Cueumis mclo seedlings by the fungus CoHletotrchum lagenarinm causes a 10-fold increase in the amount of cell wail hydroxyproline-rich glycoprotein. Evidence for this increase was provided by studying two specific markers of this glycoprotein, namely hydroxyproline and glycosylated serine. The lability of the O-glycosidic linkage of wall-bound glycosylated serine in the presence of hydrazine, was used to determine the amount of serine which is glycosylated.A large increase in the hydroxyproline content of infected plants isshown, but the ratios of glycosylated serine to hydroxyproline are similar in healthy and infected plants. As far as these markers are concerned, the hydroxyproline-rich glycoproteins secreted into the wail as a result of the disease are similar to those of healthy plants. In addition, the extent of glycosylation of the wail serine, in both healthy and infected plants, decreases as the plant ages.Serine-and hydroxyproline-rich (glyco)peptides were also isolated after trypsinolysis of the wail. These (glyco)peptides include the galactosylcontaining pentapeptide, serine-hydroxyproline4. This pentapeptide is characteristic of cell wall protein.Some aspects of the biosynthesis (4,5,27) and secretion (6) of this glycoprotein have also been studied.The present paper partially characterizes the macromolecules responsible for the 10-fold increase in hydroxyproline which occurs in the cell walls of fungal infected melon plants (10,28). This increase was formerly shown to be coincident with an increase in hydroxyproline arabinosides (12), to be dependent on protein synthesis (1 1) and paralleled by a concomitant enrichment of the wall in proteins (10, 28). These findings suggested that the synthesis of HRGP is enhanced in diseased plants. The possibility that these molecules could be unique was raised by their higher extent of hydroxyproline glycosylation than in healthy plants (12).For glycosylation of a protein to occur, the glycosyl transferases must recognize a sequence of amino acids (34). The experiments reported below were designed to determine whether the observed increased glycosylation of hydroxyproline might reflect a modification in the sequence of the amino acids at the glycosylation sites. Analyses were undertaken of the amino acid residues known to be in the vicinity of the hydroxyproline arabinosides of the wall. Hydroxyproline, serine, and particularly the ratios of glycosylated serine to total hydroxyproline were thus determined during the course of the disease and during natural aging. Hydroxyproline-rich (glyco)peptides were also isolated, with the aim of determiig their amino acid sequence.Hydroxyproline is an integral component of plant cell wall macromolecules (2,7,25,26,31, 32). It can account for up to 20%Yo of the wall amino acid residues in suspension cultured cells and is found in a hydroxyproline-rich glycoprotein (HRGP)2 that has been called "extensin" (19,20 CELL WALL GLYCOPROTEIN IN INFECTED PLANTSsodium salts, distilled H20, and acetone as...

Role of the Extensin Superfamily in Primary Cell Wall Architecture

“…Nevertheless, the idea of Idt intermolecular cross-links persisted, fueled by further evidence of in muro cross-linking (Cooper et al, 1987;Bradley et al, 1992). In particular, Bradley et al (1992) showed that fungal elicitation of hydrogen peroxide corresponded to a rapid wallhardening process involving a decrease in extractable extensin, emphasizing the significance of EsquerreTugaye's earlier work (Esquerre-Tugaye and Mazau, 1974;Esquerre-Tugaye and Lamport, 1979) and the highly specific pI 4.6 extensin peroxidase that catalyzed in vitro extensin cross-linking (Everdeen et al, 1988;Lamport, 1989). Evidence of other extensin peroxidases appeared later (Price et al, 2003).…”

“…As the structure of extensin was being determined, their involvement in disease and wound responses became apparent when Esquerre-Tugaye and colleagues showed that pathogens induced extensin accumulation and that this was correlated with disease resistance (Esquerre-Tugaye and Mazau, 1974;Esquerre-Tugaye and Lamport, 1979), while Chrispeels et al (1974) showed that physical wounding induced extensin biosynthesis. A general role for extensin in response to different stresses, including senescence and abscission, was corroborated and detailed (Merkouropoulos and Shirsat, 2003).…”

Di-isodityrosine Is the Intermolecular Cross-link of Isodityrosine-rich Extensin Analogs Cross-linked in Vitro

“…HRGPs are involved in all aspects of plant growth and development, including wall assembly during embryogenesis (4), and responses to biotic and abiotic stress that include mechanical stress (5), physical wounding (6), pathogenesis (7), and symbiosis (8 -10).…”

Purification and Partial Characterization of Tomato Extensin Peroxidase

“…Peroxidases are also believed to play a significant role in plant disease resistance. Increased peroxidase activity and elevated HRGP deposition in the cell wall have been demonstrated after challenging the plant with pathogens (Esquerré-Tugayé and Lamport, 1979;Reimers et al, 1992;Lamb et al, 1993).…”