Host-Pathogen Interactions

Abstract

Recent studies have demonstrated that an apparently homogeneous preparation of an a-1,4-D-endopolyplacturonic acid lyase (EC 4.2.2.2) isolated from the phytopathogenic bacterium Erwinia carotovora induced phytoalexin accumulation in cotyledons of soybean (Glycine max jL.1Merr. cv Wayne) and that this pectin-degrading enzyme released heatstable elicitors of phytoalexins from soybean cell walls, citrus pectin, and sodium polypectate Plant Physiol 74: 52-60). The present paper reports the purification, by anion-exchange chromatography on QAE-Sephadex columns followed by gel-permeation chromatography on a Bio-Gel P6 column, of the two fractions with highest specific elicitor activity present in a crude elicitor-preparation obtained by lyase treatment of sodium polypectate. Structural analysis of the fraction with highest specific elicitor activity indicated that the major, if not only, component was a decasaccharide of a-1,4-D-galactosyluronic acid that contained the expected product of lyase cleavage, 4-deoxy-,6-L-5-threohexopyranos-4-enyluronic acid (4,5-unsaturated galactosyluronic acid), at the nonreducing terminus. This modified decagalacturonide fraction exhibited half-maximum and maximum elicitor activity at 1 microgram/ cotyledon (6 micromolar) and 5 micrograms/cotyledon (32 micromolar) plactosyluronic acid equivalents, respectively. Reducing 90 to 95% of the carboxyl groups of the galactosyluronic acid residues abolished the elicitor activity of the decagalacturonide fraction. The second most elicitor-active fraction contained mostly undeca-a-1,4-D-galactosyluronic acid that contained 4,5-unsaturated gaactosyluronic acid at the nonreducing termini. This fraction exhibited half-maximum and maximum elicitor activity at approximately 3 micrograms/cotyledon (17 micromolar) and 6 micrograms/cotyledon (34 micromolar) galactosyluronic acid equivalents, respectively. These results confirm and extend previous observations that oligogalacturonides derived from the pectic polysaccharides of plant cell walls can serve as regulatory molecules that induce phytoalexin accumulation in soybean. These results are consistent with the hypothesis that oligogalacturonides play a role in disease resistance in plants. Although (1, 1 1). Phytoalexins are a diverse group of compounds of low mol wt that have broad antibiotic activity against many prokaryotic and eukaryotic organisms (32, 36). In some hostpathogen combinations, phytoalexins accumulate at the site of attempted infection rapidly enough and in sufficient concentration to prevent further growth of the invading microorganism (19,24).Phytoalexin accumulation is also induced by molecules called elicitors. Various compounds isolated from microorganisms have been found to have elicitor activity (reviewed in 1, 2, 6, 37). Molecules derived from plant tissues also induce phytoalexin accumulation (14-16, 23, 28).Recent work has demonstrated that a heat-labile elicitor of phytoalexins produced by the phytopathogenic bacterium Erwinia carotovora var carotovora is a p...

Plant immunity triggered by engineered in vivo release of oligogalacturonides, damage-associated molecular patterns

“…Exogenously applied OGs with a degree of polymerization (DP) between 10 and 15 activate a wide range of defense responses, including the accumulation of phytoalexins (21,22), the expression of defense-related genes (23), and the production of reactive oxygen species (24,25). Notably, application of exogenous OGs protects plants against subsequent fungal infection (26,27).…”

Arabidopsis MPK3 and MPK6 Play Different Roles in Basal and Oligogalacturonide- or Flagellin-Induced Resistance against Botrytis cinerea

“…The accumulation of active OGs, with a degree of polymerization between 10 and 15, is favored by the presence of polygalacturonase-inhibiting proteins in the apoplast (De Lorenzo and Ferrari, 2002;Casasoli et al, 2009). OGs elicit a variety of responses, including the production of reactive oxygen species (ROS; Bellincampi et al, 2000;Galletti et al, 2008), a rapid modification of membrane polarization and ion fluxes (Mathieu et al, 1991;Thain et al, 1995), the induction of defense-related genes, and the accumulation of phytoalexins (Davis et al, 1986). Activation of defense responses by OGs increases resistance of Arabidopsis (Arabidopsis thaliana) and grape (Vitis vinifera) leaves against the necrotrophic fungus Botrytis cinerea (Aziz et al, 2004;Ferrari et al, 2007).…”

A 4,5-unsaturated low molecular oligogalacturonide as a potent phytoalexin-elicitor isolated from polygalacturonide of Ficus awkeotsang.

“…was put onto a column of QAE-Sephadex A-25, which was pre- with lOO mM imidazole-HCl buffer, pH 7.0. Figure 2 shows an elution profile of the high-resolution chromatography of the de-esterified awkeotsang OLGAs (peaks [1][2][3][4][5][6][7][8][9][10][11][12]. It was presumed that each fraction corresponds to an OLGAhaving definite degree of polymerization.…”

“…Xenonwas used as the bombarding gas, and the atom gun was operated at 6kV, 20mA. Samples were dissolved in methanol-water (1)(2)(3)(4)(5) fig/fil) and a sample (1 }A) was added to a drop ofglycerol on the stainless steel target.…”