Lotus japonicus Forms Early Senescent Root Nodules with Rhizobium etli

Abstract

Mesorhizobium loti and Rhizobium etli are microsymbionts of the Lotus and Phaseolus spp., respectively, and secrete essentially the same Nod factors. Lotus japonicus efficiently formed root nodules with R. etli CE3, irrespective of the presence or absence of a flavonoid-independent transcription activator nodD gene. On a nitrogen-free medium, however, the host plant inoculated with R. etli showed a severe nitrogen deficiency symptom. Initially, the nodules formed with R. etli were pale pink and leghemoglobin mRNA was detectable at significant levels. Nevertheless, the nodules became greenish with time. Acetylene-reduction activity of nodules formed with R. etli was comparable with that formed by M. loti 3 weeks postinoculation, but thereafter it decreased rapidly. The nodules formed with R. etli contained much more starch granules than those formed with M. loti. R. etli developed into bacteroids in the L. japonicus nodules, although the density of bacteroids in the infected cells was lower than that in the nodules formed with M. loti. The nodules formed with R. etli were of the early senescence type, in that membrane structures were drastically disintegrated in the infected cells of the greenish nodules. Thus, L. japonicus started and then ceased a symbiotic relationship with R. etli at the final stage.

Rhizobium etli CE3 Bacteroid Lipopolysaccharides Are Structurally Similar but Not Identical to Those Produced by Cultured CE3 Bacteria

“…A transmission electron microscopy analysis of band 4 material demonstrated that it consisted of elongated organisms primarily occupied with low electron-dense material (Fig. 3C), reportedly identified as polyhydroxybutyrate typically found in Rhizobium bacteroids (32). This image was similar to that observed for CE3 bacteroids present in the central nitrogen-fixing tissue of mature P. vulgaris nodules (Fig.…”

“…To identify which band contained the CE3 bacteroids, the material obtained in each band was stained with crystal violet and safranin and observed using light microscopy. Only band 4 appeared to be pure and consisted solely of elongated structures with a shape that was similar to that of CE3 bacteroids (32,33). All other bands were impure and mainly contained plant cell debris (bands 1 and 2) and clusters or single round-shaped bacterialike structures (bands 3 and 5).…”

A Mesorhizobium loti mutant with reduced glucan content shows defective invasion of its host plant Lotus japonicus

“…The specificity between rhizobia and host legumes is also exhibited at stages later than those at which Nod factors act. This is exemplified in the symbiotic phenotype of Rhizobium etli on L. japonicus, in which early nodule senescence occurs despite the fact that the Nod factors from M. loti and R. etli have the same structure (Banba et al, 2001). To fully understand the molecular basis for the interaction between the model symbiotic pair M. loti and L. japonicus, additional symbiotic genes need to be identified extensively in the M. loti genome.…”

Aging in Legume Symbiosis. A Molecular View on Nodule Senescence in Medicago truncatula

“…Nodule senescence can be triggered prematurely by various types of stress (Gogorcena et al, 1997;González et al, 1998;Matamoros et al, 1999) or as a consequence of deficient recognition between partners (Banba et al, 2001). This induced nodule senescence develops much more rapidly than developmental senescence and present features of oxidative stress and plant cell death (Puppo et al, 2005).…”