Nodule development induced by Mesorhizobium loti mutant strains affected in polysaccharide synthesis

• Published in: Molecular plant-microbe interactions Vol. 18; no. 5; pp. 446 - 457
• Main Authors: D'Antuono, A.L, Casabuono, A, Couto, A, Ugalde, R.A, Lepek, V.C
• Format: Journal Article
• Language: English
• Published: St Paul, MN APS Press 01-05-2005; American Phytopathological Society; The American Phytopathological Society
• Subjects: Bacterial plant pathogens; bacterial proteins; Biological and medical sciences; biosynthesis; Calcium; Culture Media; cyclic beta(1,2)-glucan synthase; enzyme activity; epimerase/dehydratase family; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial - physiology; Genes, Bacterial - physiology; glycosyl-transferases; glycosyltransferases; lipopolysaccharides; Lipopolysaccharides - metabolism; Loteae - microbiology; Loteae - physiology; LPS and β(1-2) cyclic glucan mutants; Mesorhizobium loti; molecular sequence data; Mutation; nodulation; nucleotide sequences; Phenotype; Phytopathology. Animal pests. Plant and forest protection; Plant Roots - microbiology; Plant Roots - physiology; Rhizobiaceae - genetics; Rhizobiaceae - metabolism; Rhizobiaceae - physiology; root nodules; LPS and β(1-2) cyclic glucan mutants; Gene cluster; glycosyltransferases; Enzyme; Nodulation; Chromosome; Homology; Lotus; Strain; Glucan; Leguminosae; Enzymatic activity; O antigen; Dicotyledones; Angiospermae; Lipopolysaccharide; Spermatophyta; Mutation; epimerase/dehydratase family; Polysaccharide
• ISSN: 0894-0282; 1943-7706
• DOI: 10.1094/mpmi-18-0446

The role of Mesorhizobium loti surface polysaccharides on the nodulation process is not yet fully understood. In this article, we describe the nodulation phenotype of mutants affected in the synthesis of lipopolysaccharide (LPS) and beta(1,2) cyclic glucan. M. loti lpsbeta2 mutant produces LPS with reduced amount of O-antigen, whereas M. loti lpsbeta1 mutant produces LPS totally devoid of O-antigen. Both genes are clustered in the chromosome. Based on amino acid sequence homology, LPS sugar composition, and enzymatic activity, we concluded that lpsbeta2 codes for an enzyme involved in the transformation of dTDP-glucose into dTDP-rhamnose, the sugar donor of rhamnose for the synthesis of O-antigen. On the other hand, lpsbeta1 codes for a glucosyltransferase involved in the biosynthesis of the O-antigen. Although LPS mutants elicited normal nodules, both show reduced competitiveness compared with the wild type. M. loti beta(1-2) cyclic glucan synthase (cgs) mutant induces white, empty, ineffective pseudonodules in Lotus tenuis. Cgs mutant induces normal root hair curling but is unable to induce the formation of infection threads. M. loti cgs mutant was more sensitive to deoxycholate and displayed motility impairment compared with the wild-type strain. This pleiotropic effect depends on calcium concentration and temperature.