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Rhizobial Secretion of Truncated Exopolysaccharides Severely Impairs the Mesorhizobium-Lotus Symbiosis

Journal Article · · Molecular Plant-Microbe Interactions
 [1];  [2];  [3];  [1];  [1];  [3];  [3];  [2];  [1]
  1. University of Otago, Dunedin (New Zealand)
  2. University of Georgia, Athens, GA (United States)
  3. Aarhus University (Denmark)
+ Show Author Affiliations
The symbiosis between Mesorhizobium japonicum R7A and Lotus japonicus Gifu is an important model system for investigating the role of bacterial exopolysaccharides (EPS) in plant-microbe interactions. Previously, we showed that R7A exoB mutants that are affected at an early stage of EPS synthesis and in lipopolysaccharide (LPS) synthesis induce effective nodules on L. japonicus Gifu after a delay, whereas exoU mutants affected in the biosynthesis of the EPS side chain induce small uninfected nodule primordia and are impaired in infection. The presence of a halo around the exoU mutant when grown on Calcofluor-containing media suggested the mutant secreted a truncated version of R7A EPS. A nonpolar ΔexoA mutant defective in the addition of the first glucose residue to the EPS backbone was also severely impaired symbiotically. Here, we used a suppressor screen to show that the severe symbiotic phenotype of the exoU mutant was due to the secretion of an acetylated pentasaccharide, as both monomers and oligomers, by the same Wzx/Wzy system that transports wild-type exopolysaccharide. We also present evidence that the ΔexoA mutant secretes an oligosaccharide by the same transport system, contributing to its symbiotic phenotype. In contrast, ΔexoYF and polar exoA and exoL mutants have a similar phenotype to exoB mutants, forming effective nodules after a delay. These studies provide substantial evidence that secreted incompatible EPS is perceived by the plant, leading to abrogation of the infection process.
Research Organization:
University of Georgia, Athens, GA (United States)
Sponsoring Organization:
Novo Nordisk Foundation; USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0015662
OSTI ID:
2530608
Journal Information:
Molecular Plant-Microbe Interactions, Journal Name: Molecular Plant-Microbe Interactions Journal Issue: 9 Vol. 37; ISSN 0894-0282
Publisher:
APS Press - International Society for Molecular Plant-Microbe InteractionsCopyright Statement
Country of Publication:
United States
Language:
English

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  • Acosta-Jurado, Sebastián; Fuentes-Romero, Francisco; Ruiz-Sainz, Jose-Enrique
  • International Journal of Molecular Sciences, Vol. 22, Issue 12 https://doi.org/10.3390/ijms22126233
journal June 2021
The Role of Flavonoids in Nodulation Host-Range Specificity: An Update journal August 2016

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Related Subjects

59 BASIC BIOLOGICAL SCIENCES
Mesorhizobium-Lotus symbiosis
exo mutants
exopolysaccharide secretion
truncated exopolysaccharide