Defense and senescence interplay in legume nodules.

Immunity and senescence play a crucial role in the functioning of the legume symbiotic nodules. The miss-regulation of one of these processes compromises the symbiosis leading to death of the endosymbiont and the arrest of the nodule functioning. The relationship between immunity and senescence has been extensively studied in plant organs where a synergistic response can be observed.

Insight into the control of nodule immunity and senescence during Medicago truncatula symbiosis.

Medicago (Medicago truncatula) establishes a symbiosis with the rhizobia Sinorhizobium sp, resulting in the formation of nodules where the bacteria fix atmospheric nitrogen. The loss of immunity repression or early senescence activation compromises symbiont survival and leads to the formation of nonfunctional nodules (fix-). Despite many studies exploring an overlap between immunity and senescence responses outside the nodule context, the relationship between these processes in the nodule remains poorly understood.

Medicago-Sinorhizobium-Ralstonia Co-infection Reveals Legume Nodules as Pathogen Confined Infection Sites Developing Weak Defenses.

Legumes have the capacity to develop root nodules hosting nitrogen-fixing bacteria, called rhizobia. For the plant, the benefit of the symbiosis is important in nitrogen-deprived conditions, but it requires hosting and feeding massive numbers of rhizobia. Recent studies suggest that innate immunity is reduced or suppressed within nodules [1-10]; this likely maintains viable rhizobial populations.

Legume Nodules: Massive Infection in the Absence of Defense Induction.

Plants of the legume family host massive intracellular bacterial populations in the tissues of specialized organs, the nodules. In these organs, the bacteria, named rhizobia, can fix atmospheric nitrogen and transfer it to the plant. This special metabolic skill provides to the legumes an advantage when they grow on nitrogen-scarce substrates.

The Multiple Faces of the Medicago-Sinorhizobium Symbiosis.

Medicago truncatula is able to perform a symbiotic association with Sinorhizobium spp. This interaction leads to the formation of a new root organ, the nodule, in which bacteria infect the host cells and fix atmospheric nitrogen for the plant benefit. Multiple and complex processes are essential for the success of this interaction from the recognition phase to nodule formation and functioning, and a wide range of plant host genes is required to orchestrate this phenomenon.

Control of the ethylene signaling pathway prevents plant defenses during intracellular accommodation of the rhizobia.

Massive intracellular populations of symbiotic bacteria, referred to as rhizobia, are housed in legume root nodules. Little is known about the mechanisms preventing the development of defense in these organs although genes such as SymCRK and DNF2 of the model legume Medicago truncatula are required for this control after rhizobial internalization in host nodule cells. Here we investigated the molecular basis of the symbiotic control of immunity.

Multiple steps control immunity during the intracellular accommodation of rhizobia.

Medicago truncatula belongs to the legume family and forms symbiotic associations with nitrogen fixing bacteria, the rhizobia. During these interactions, the plants develop root nodules in which bacteria invade the plant cells and fix nitrogen for the benefit of the plant. Despite massive infection, legume nodules do not develop visible defence reactions, suggesting a special immune status of these organs.

Rhizobium-legume symbioses: the crucial role of plant immunity.

New research results have significantly revised our understanding of the rhizobium-legume infection process. For example, Nod factors (NFs), previously thought to be absolutely essential for this symbiosis, were shown to be dispensable under particular conditions. Similarly, an NF receptor, previously considered to be solely involved in symbiosis, was shown to function during plant pathogen infections.

A nonRD receptor-like kinase prevents nodule early senescence and defense-like reactions during symbiosis.

Rhizobia and legumes establish symbiotic interactions leading to the production of root nodules, in which bacteria fix atmospheric nitrogen for the plant's benefit. This symbiosis is efficient because of the high rhizobia population within nodules. Here, we investigated how legumes accommodate such bacterial colonization.

Growth conditions determine the DNF2 requirement for symbiosis.

Rhizobia and legumes are able to interact in a symbiotic way leading to the development of root nodules. Within nodules, rhizobia fix nitrogen for the benefit of the plant. These interactions are efficient because spectacularly high densities of nitrogen fixing rhizobia are maintained in the plant cells.

Failure of self-control: defense-like reactions during legume/rhizobia symbiosis.

Medicago truncatula and Sinorhizobium meliloti form a symbiotic association resulting in the formation of nitrogen-fixing nodules. In this organ, symbiotic cells contain large numbers of bacteroids. Remarkably, this chronic infection does not trigger visible defense reactions.