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Conditional requirement for exopolysaccharide in the Mesorhizobium-Lotus symbiosis.
- Source :
-
Molecular plant-microbe interactions : MPMI [Mol Plant Microbe Interact] 2013 Mar; Vol. 26 (3), pp. 319-29. - Publication Year :
- 2013
-
Abstract
- Rhizobial surface polysaccharides are required for nodule formation on the roots of at least some legumes but the mechanisms by which they act are yet to be determined. As a first step to investigate the function of exopolysaccharide (EPS) in the formation of determinate nodules, we isolated Mesorhizobium loti mutants affected in various steps of EPS biosynthesis and characterized their symbiotic phenotypes on two Lotus spp. The wild-type M. loti R7A produced both high molecular weight EPS and lower molecular weight (LMW) polysaccharide fractions whereas most mutant strains produced only LMW fractions. Mutants affected in predicted early biosynthetic steps (e.g., exoB) formed nitrogen-fixing nodules on Lotus corniculatus and L. japonicus 'Gifu', whereas mutants affected in mid or late biosynthetic steps (e.g., exoU) induced uninfected nodule primordia and, occasionally, a few infected nodules following a lengthy delay. These mutants were disrupted at the stage of infection thread (IT) development. Symbiotically defective EPS and Nod factor mutants functionally complemented each other in co-inoculation experiments. The majority of full-length IT observed harbored only the EPS mutant strain and did not show bacterial release, whereas the nitrogen-fixing nodules contained both mutants. Examination of the symbiotic proficiency of the exoU mutant on various L. japonicus ecotypes revealed that both host and environmental factors were linked to the requirement for EPS. These results reveal a complex function for M. loti EPS in determinate nodule formation and suggest that EPS plays a signaling role at the stages of both IT initiation and bacterial release.
- Subjects :
- Bacterial Proteins genetics
Bacterial Proteins metabolism
Genes, Reporter
Genotype
Lotus growth & development
Lotus ultrastructure
Mesorhizobium growth & development
Mesorhizobium metabolism
Mesorhizobium ultrastructure
Mutagenesis
Mutagenesis, Insertional
Nitrogen Fixation
Phenotype
Plant Roots growth & development
Plant Roots microbiology
Plant Roots ultrastructure
Polysaccharides, Bacterial genetics
Polysaccharides, Bacterial isolation & purification
Root Nodules, Plant genetics
Root Nodules, Plant growth & development
Root Nodules, Plant microbiology
Root Nodules, Plant ultrastructure
Seedlings growth & development
Seedlings microbiology
Seedlings ultrastructure
Uronic Acids analysis
Uronic Acids metabolism
Lotus microbiology
Mesorhizobium genetics
Polysaccharides, Bacterial metabolism
Symbiosis
Subjects
Details
- Language :
- English
- ISSN :
- 0894-0282
- Volume :
- 26
- Issue :
- 3
- Database :
- MEDLINE
- Journal :
- Molecular plant-microbe interactions : MPMI
- Publication Type :
- Academic Journal
- Accession number :
- 23134480
- Full Text :
- https://doi.org/10.1094/MPMI-09-12-0227-R