title: Low molecular weight EPS II of Rhizobium meliloti allows nodule invasion in Medicago sativa.
abstract: Effective invasion of alfalfa by Rhizobium meliloti Rm1021 normally requires the presence of succinoglycan, an exopolysaccharide (EPS) produced by the bacterium. However, Rm1021 has the ability to produce a second EPS (EPS II) that can suppress the symbiotic defects of succinoglycan-deficient strains. EPS II is a polymer of modified glucose-(beta-1,3)-galactose subunits and is produced by Rm1021 derivatives carrying either an expR101 or mucR mutation. If the ability to synthesize succinoglycan is blocked genetically, expR101 derivatives of Rm1021 are nodulation-proficient, whereas mucR derivatives of Rm1021 are not. The difference in nodulation proficiency between these two classes of EPS II-producing strains is due to the specific production of a low molecular weight form of EPS II by expR101 strains. A low molecular weight EPS II fraction consisting of 15-20 EPS II disaccharide subunits efficiently allows nodule invasion by noninfective strains when present in amounts as low as 7 pmol per plant, suggesting that low molecular weight EPS II may act as a symbiotic signal during infection.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge 02139, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: González
authors.forename: B L
authors.initials: BL
authors.lastname: Reuhs
authors.forename: G C
authors.initials: GC
authors.lastname: Walker
mesh_terms: D005816:Genetic Complementation Test; D000455:Medicago sativa / Q000382:microbiology*; D008970:Molecular Weight; D009586:Nitrogen Fixation; D011135:Polysaccharides, Bacterial / Q000737:chemistry / Q000378:metabolism; D012231:Rhizobium / Q000472:pathogenicity*; D013559:Symbiosis
chemical_list: D011135:Polysaccharides, Bacterial; C056779:succinoglycan