Differences in the Methyl Ester Distribution of Homogalacturonans from Near-Isogenic Wheat Lines Resistant and Susceptible to the Wheat Stem Rust Fungus

Abstract

Plants possess an efficient nonself surveillance system triggering induced disease resistance mechanisms upon molecular recognition of microbial invaders. Successful pathogens have evolved strategies to evade or counteract these mechanisms, e.g., by the generation of suppressors. Pectic fragments produced during host cell wall degradation can act as endogenous suppressors of the hypersensitive response in wheat leaves. We have isolated and characterized homogalacturonans from cell walls of two wheat cultivars susceptible to the stem rust fungus, Puccinia graminis f. sp. tritici, namely cvs. Prelude and Marquis, and from near-isogenic lines of both cultivars containing the Sr5-gene for hypersensitive rust resistance. Two independent approaches were used to compare their methyl esterification: i) immunochemistry using the monoclonal antibodies JIM5, JIM7, PAM1, and LM7 and ii) chromatography of oligogalacturonides representing stretches of contiguous nonmethyl-esterified GalA residues. The results clearly indicate a significant difference in the homogalacturonans from susceptible and resistant wheat lines. The difference can best be explained by assuming a nonrandom and more blockwise distribution of the methyl esters in the homogalacturonans of susceptible wheat cultivars as compared with a presumably more random distribution in the near-isogenic resistant lines. Possible consequences of this difference for the enzymatic generation of endogenous suppressors are discussed.

Cellulose Binding Protein from the Parasitic Nematode Heterodera schachtii Interacts with Arabidopsis Pectin Methylesterase: Cooperative Cell Wall Modification during Parasitism

“…The enlarged size of plants overexpressing CBP or PME3 may be attributable to this type of PME action. It has been suggested that PMEs also have a role in resistance to fungal and bacterial pathogens (McMillan et al, 1993;Boudart et al, 1998;Wietholter et al, 2003) by affecting the physicochemical properties of the cell wall to be more accessible to cell wall-digesting enzymes (Lionetti et al, 2007). Interestingly, we did not find significant effects of CBP or PME3 on plant susceptibility to M. incognita.…”

Arabidopsis PECTIN METHYLESTERASEs Contribute to Immunity against Pseudomonas syringae

“…The difference in pectin release by polygalacturonases was diminished after PME treatment (LeCam et al, 1994), suggesting that differences in methylester distribution rather than total degree of esterification affected pathogen success. Moreover, in wheat (Triticum aestivum) near-isogenic lines, a blockwise distribution of methylesters was detected in lines susceptible to Puccinia graminis compared with a more random distribution in resistant lines (Wiethölter et al, 2003). In addition, the elicitor activity of OGs is dependent on the degree and distribution of methylesters (Cabrera et al, 2008;Osorio et al, 2008).…”

Protein expression during seed development in Araucaria angustifolia: transient accumulation of class IV chitinases and arabinogalactan proteins

“…Monosaccharide composition of seed AGPs was determined by gas liquid chromatography (GLC) using inositol as an internal standard (Wiethö lter et al 2003). A solution containing 100 mg of AGPs was lyophilized, then methanolized in 1.5 M methanolic-HCL at 80 C overnight.…”