Legumes form symbioses with rhizobia, producing nitrogen-fixing nodules on the roots of the plant host. The network of plant signaling pathways affecting carbon metabolism may determine the final number of nodules. The trehalose biosynthetic pathway regulates carbon metabolism and plays a fundamental role in plant growth and development, as well as in plant-microbe interactions. The expression ...

Actinorhizal plants invade nitrogen-poor soils because of their ability to form root nodule symbioses with N(2)-fixing actinomycetes known as Frankia. Frankia strains are difficult to isolate, so the diversity of strains inhabiting nodules in nature is not known. To address this problem, we have used the variability in bacterial 16S rRNA gene sequences amplified from root nodules as a means to ...

We investigated the presence of endophytic rhizobia within the roots of the wetland wild rice Oryza breviligulata, which is the ancestor of the African cultivated rice Oryza glaberrima. This primitive rice species grows in the same wetland sites as Aeschynomene sensitiva, an aquatic stem-nodulated legume associated with photosynthetic strains of Bradyrhizobium. Twenty endophytic and aquatic iso...

N2-fixing symbiotic root nodules of the actinorhizal host Datisca glomerata express Dgrca (D. glomerata Rubisco activase) mRNA, a transcript usually associated with photosynthetic organs or tissues. In northern blots a mature, 1700-nucleotide Dgrca mRNA was detected in green plant organs (leaves, flowers, and developing fruits) and in nodules but was not detected in roots. A second message of 3...

The tropical legume Sesbania rostrata can be nodulated by Azorhizobium caulinodans on both its stem and its root system. Here we investigate in detail the process of root nodulation and show that nodules develop exclusively at the base of secondary roots. Intercellular infection leads to the formation of infection pockets, which then give rise to infection threads. Concomitantly with infection,...

Root-nodule symbiosis between leguminous plants and nitrogen-fixing bacteria (rhizobia) involves molecular communication between the two partners. Key components for the establishment of symbiosis are rhizobium-derived lipochitooligosaccharides (Nod factors; NFs) and their leguminous receptors (NFRs) that initiate nodule development and bacterial entry. Here we demonstrate that the soybean micr...

The plant plasma membrane-localized NADPH oxidases, known as respiratory burst oxidase homologues (RBOHs), appear to play crucial roles in plant growth and development. They are involved in important processes, such as root hair growth, plant defence reactions and abscisic acid signalling. Using sequence similarity searches, we identified seven putative RBOH-encoding genes in the Medicago trunc...

We have determined the structure of a polysaccharide from strain B33, a fast-growing bacterium that forms nitrogen-fixing nodules with Asiatic and American soya bean cultivars. On the basis of monosaccharide analysis, methylation analysis, one-dimensional 1H- and 13C-NMR and two-dimensional NMR experiments, the structure was shown to consist of a polymer having the repeating unit -->6)-4-O-meth...

Rhizobia are nitrogen-fixing bacteria that establish endosymbiotic associations with legumes. Nodule formation depends on various bacterial carbohydrates, including lipopolysaccharides, K-antigens, and exopolysaccharides (EPS). An acidic EPS from Rhizobium sp. strain NGR234 consists of glucosyl (Glc), galactosyl (Gal), glucuronosyl (GlcA), and 4,6-pyruvylated galactosyl (PvGal) residues with be...

Frankia spp. are filamentous actinomycetes that fix N2 in culture and in actinorhizal root nodules. In combined nitrogen-depleted aerobic environments, nitrogenase is restricted to thick-walled spherical structures, Frankia vesicles, that are formed on short stalks along the vegetative hyphae. The activities of the NH4(+)-assimilating enzymes (glutamine synthetase [GS], glutamate synthase, glut...