Conditional Requirement for Exopolysaccharide in the Mesorhizobium–Lotus Symbiosis

• DOI: 10.1094/mpmi-09-12-0227-r
• Publication Date: 2012-11-07T19:16:14Z
• Authors: Simon J. Kelly; Artur Muszyński; Yasuyuki Kawaharada; Andree M. Hubber; John T. Sullivan; Niels Sandal; Russell W. Carlson; Jens Stougaard; Clive W. Ronson
• Keywords: Lotus japonicus; Lotus corniculatus; Nod factor; Mesorhizobium

Rhizobial surface polysaccharides are required for nodule formation on the roots of at least some legumes but mechanisms by which they act yet to be determined. As a first step investigate function exopolysaccharide (EPS) in determinate nodules, we isolated Mesorhizobium loti mutants affected various steps EPS biosynthesis and characterized their symbiotic phenotypes two Lotus spp. The wild-type M. R7A produced both high molecular weight lower (LMW) polysaccharide fractions whereas most mutant strains only LMW fractions. Mutants predicted early biosynthetic (e.g., exoB) formed nitrogen-fixing nodules corniculatus L. japonicus ‘Gifu’, mid or late exoU) induced uninfected primordia and, occasionally, few infected following lengthy delay. These were disrupted stage infection thread (IT) development. Symbiotically defective Nod factor functionally complemented each other co-inoculation experiments. majority full-length IT observed harbored strain did not show bacterial release, contained mutants. Examination proficiency exoU ecotypes revealed that host environmental factors linked requirement EPS. results reveal complex suggest plays signaling role stages initiation release.