Lectin-enhanced accumulation of manganese-limited Rhizobium leguminosarum cells on pea root hair tips

Abstract

The ability of Rhizobium leguminosarum 248 to attach to developing Pisum sativum root hairs was investigated during various phases of bacterial growth in yeast extract-mannitol medium. Direct cell counting revealed that growth of the rhizobia transiently stopped three successive times during batch culture in yeast extract-mannitol medium. These interruptions of growth, as well as the simultaneous autoagglutination of the bacteria, appeared to be caused by manganese limitation. Rhizobia harvested during the transient phases of growth inhibition appeared to have a better attachment ability than did exponentially growing rhizobia. The attachment characteristics of these manganese-limited rhizobia were compared with those of carbon-limited rhizobia (G. Smit, J. W. Klne, and B. J. J. Lugtenberg, J. Bacteriol. 168:821-827, 1986, and J. Bacteriol. 169:4294-4301, 1987). In contrast to the attachment of carbon-limited cells, accumulation of manganeselimited rhizobia (cap formation) was already in full progress after 10 min of incubation; significantly delayed by 3-0-methyl-D-glucose, a pea lectin haptenic monosaccharide; partially resistant to sodium chloride; and partially resistant to pretreatment of the bacteria with cellulase. Binding of single bacteria to the root hair tips was not inhibited by 3-0-methyl-D-glucose. Whereas attachment of single R. leguminosarum cells to the surface of pea root hair tips seemed to be similar for both carbon-and manganese-limited cells, the subsequent accumulation of manganese-limited rhizobia at the root hair tips is apparently accelerated by pea lectin molecules. Moreover, spot inoculation tests with rhizobia grown under various culture conditions indicated that differences in attachment between manganese-and carbon-limited R. kguminosarum cells are correlated with a significant difference in infectivity in that manganese-limited rhizobia, in contrast to carbon-limited rhizobia, are infective. This growth-medium-dependent behavior offers an explanation for the seemingly conflicting data on the involvement of host plant lectins in attachment of rhizobia to root hairs of leguminous plants. Sym plasmid-borne genes do not play a role in manganese-limitation-induced attachment of R. keguminosarum.Attachment of rhizobia to tips of developing root hairs of leguminous plants is thought to be an early and necessary step in the infection process leading to the development of nitrogen-fixing root nodules. The physical interaction between rhizobia and the growing root hair tips precedes the following infection stages in the nodulation process: marked root hair curling, infection thread formation, development of a root cortical meristem, and root nodule morphogenesis (7). Nodulation is a host-plant-specific process; e.g., Rhizobium leguminosarum (R. leguminosarum biovar viciae) exclusively nodulates pea, vetch, lentil, and sweet pea, whereas Rhizobium trifolii (R. leguminosarum biovar trifolii) nodulates only clover. Host specificity is determined by one or more events preceding the outgrowth o...

A unipolarly located, cell-surface-associated agglutinin, RapA, belongs to a family of Rhizobium-adhering proteins (Rap) in Rhizobium leguminosarum bv. trifolii The GenBank accession numbers for the sequences reported in this paper are AF265222, AF265223, AF315809 and AF315810.

“…The direct binding mediated by rhicadhesin is followed by a step of clustering and firm attachment of the bacteria to the root hair surface, mediated by rhizobial cellulose fibres. Under manganese limitation also the plant lectin is involved in this interaction between bacteria and root hairs (Smit et al, 1987 ;Kijne et al, 1988). However, validation of this model is difficult since, to our knowledge, there are no reports describing the cloning of the gene for rhicadhesin or isolation of mutants defective in rhicadhesin activity.…”

Genetic derepression of a developmentally regulated lipopolysaccharide antigen from Rhizobium leguminosarum 3841

“…Cellulose fibrils and calcium-dependent adhesins may be involved in the earliest stages of root hair attachment (41), before a possible surface interaction with plant lectins (18,19,27). Extracellular acidic polysaccharide is apparently needed to permit plant cell infection in many legumes (30), although extracellular polysaccharide-negative mutants of Rhizobium leguminosarum bv.…”

A Peanut Nodule Lectin in Infected Cells and in Vacuoles and the Extracellular Matrix of Nodule Parenchyma

“…increase the numbers of invasive rhizobia at infectible sites by agglutinating the bacteria via cell surface haptens (e.g. Kijne et al, 1988). Root lectins have also been touted as a possible factor in determining the host-specificity of infection by homologous rhizobia (Bohlool and Schmidt, 1974).…”

“…Secreted lectin is thought to enhance agglutination of potential symbionts in the family Rhizobiaceae on infectible root hairs (Kijne et al, 1988). In most important crop legumes, rhizobia invade the root via an infection structure called an infection thread.…”