Oligogalacturonides: Novel Signaling Molecules in Rhizobium-Legume Communications

• Published in: Molecular plant-microbe interactions Vol. 25; no. 11; pp. 1387 - 1395
• Main Authors: MOSCATIELLO, Roberto, BALDAN, Barbara, SQUARTINI, Andrea, MARIANI, Paola, NAVAZIO, Lorella
• Format: Journal Article
• Language: English
• Published: St. Paul, MN APS Press 01-11-2012; The American Phytopathological Society
• Subjects: Agronomy. Soil science and plant productions; Bacteria; Biological and medical sciences; Calcium; Calcium (intracellular); Calcium - metabolism; Catalase; Colonization; Communication; Deposits; Economic plant physiology; Fabaceae - metabolism; Fabaceae - microbiology; Flavonoids; Fluorescence; Fundamental and applied biological sciences. Psychology; katG gene; Legumes; Naringenin; Nitrogen Fixation - physiology; Nod protein; oligogalacturonides; Oligosaccharides - metabolism; Phytopathology. Animal pests. Plant and forest protection; Plant cells; Polymerization; Renilla-luciferin 2-monooxygenase; Rhizobium leguminosarum; Rhizobium leguminosarum - metabolism; Rhizobium leguminosarum - physiology; Rhizosphere; Roots; Signal Transduction - physiology; Symbiosis; Symbiosis (nodules, symbiotic nitrogen fixation, mycorrhiza...); Bacteria; Plant; Rhizobium; Rhizobiaceae; Symbiont
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/MPMI-03-12-0066-R

Oligogalacturonides are pectic fragments of the plant cell wall, whose signaling role has been described thus far during plant development and plant-pathogen interactions. In the present work, we evaluated the potential involvement of oligogalacturonides in the molecular communications between legumes and rhizobia during the establishment of nitrogen-fixing symbiosis. Oligogalacturonides with a degree of polymerization of 10 to 15 were found to trigger a rapid intracellular production of reactive oxygen species in Rhizobium leguminosarum bv. viciae 3841. Accumulation of H(2)O(2), detected by both 2',7'-dichlorodihydrofluorescein diacetate-based fluorescence and electron-dense deposits of cerium perhydroxides, was transient and did not affect bacterial cell viability, due to the prompt activation of the katG gene encoding a catalase. Calcium measurements carried out in R. leguminosarum transformed with the bioluminescent Ca(2+) reporter aequorin demonstrated the induction of a rapid and remarkable intracellular Ca(2+) increase in response to oligogalacturonides. When applied jointly with naringenin, oligogalacturonides effectively inhibited flavonoid-induced nod gene expression, indicating an antagonistic interplay between oligogalacturonides and inducing flavonoids in the early stages of plant root colonization. The above data suggest a novel role for oligogalacturonides as signaling molecules released in the rhizosphere in the initial rhizobium-legume interaction.