Signals in Root Nodule Organogenesis and Endocytosis of Rhizobium.

Key Role of Bacterial NH 4 + Metabolism in Rhizobium-Plant Symbiosis

“…This implies that the IC may take up solutes, such as sugars, not only from the extracellular space but also from the peribacteroid space of the youngest BTs. However, later on during differentiation, the structure and function of the SB membrane as well as the composition of the peribacteroid space gradually change (200,201). For instance, the induction of a C 4 -dicarboxylate carrier on the SB membrane (138) may drastically change the physiology of the SBs.…”

Rhizobium meliloti elicits transient expression of the early nodulin gene ENOD12 in the differentiating root epidermis of transgenic alfalfa.

“…Recent research has shown that multiple signal exchange is essential for the correct recognition between the plant and the microsymbiont (for reviews, see Long, 1989;Fisher and Long, 1992;Verma, 1992). In particular, rhizobial nodulation (nod) genes, whose transcription requires plant flavonoids, are responsible for the synthesis of extracellular lipooligosaccharides that mediate the specific symbiotic interaction with the legume host (D6narié and Roche, 1992).…”

A cysG mutant strain of Rhizobium etli pleiotropically defective in sulfate and nitrate assimilation

“…From the point of view of the bacterial partner, the development of these new plant organs is a multistage process involving bacterial multiplication in the rhizosphere, the recognition and infection of the root hairs, bacterial growth inside a network of infection threads, and the release of bacteria from the threads into the cytoplasm of host cells. Within the infected plant cells, the bacteria differentiate into nondividing bacteroids which are equivalent to plant cell organelles able to reduce atmospheric dinitrogen (28,30).In poor soils, where Rhizobium-legume symbiosis takes place, and prior to the onset of N 2 fixation, the host plant should provide nutrients (e.g., carbon, nitrogen, and sulfur sources) to support the growth of the developing nodules. It has recently been proposed (6) that bacterial nutrients are delivered by the plant only at the tip (and not at the base) of the infection threads, where bacterial growth was observed.…”

“…From the point of view of the bacterial partner, the development of these new plant organs is a multistage process involving bacterial multiplication in the rhizosphere, the recognition and infection of the root hairs, bacterial growth inside a network of infection threads, and the release of bacteria from the threads into the cytoplasm of host cells. Within the infected plant cells, the bacteria differentiate into nondividing bacteroids which are equivalent to plant cell organelles able to reduce atmospheric dinitrogen (28,30).…”