Symbiosis specificity in the legume - rhizobial mutualism

Abstract

SummaryLegume plants are able to engage in root nodule symbiosis with nitrogen-fixing soil bacteria, collectively called rhizobia. This mutualistic association is highly specific, such that each rhizobial species/ strain interacts with only a specific group of legumes, and vice versa. Symbiosis specificity can occur at multiple phases of the interaction, ranging from initial bacterial attachment and infection to late nodule development associated with nitrogen fixation. Genetic control of symbiosis specificity is complex, involving fine-tuned signal communication between the symbiotic partners. Here we review our current understanding of the mechanisms used by the host and bacteria to choose their symbiotic partners, with a special focus on the role that the host immunity plays in controlling the specificity of the legume -rhizobial symbiosis.

Burkholderia bacteria infectiously induce the proto-farming symbiosis of Dictyostelium amoebae and food bacteria

“…Taken together, this horizontal transfer suggests that little coevolution may be needed for the formation of novel symbiosis. However, in some plant-rhizobia or -mycorrhizal associations, the symbiont phenotype can vary substantially among hosts, and the outcome of the association is determined by the interaction of host and symbiont-derived factors (34)(35)(36)(37)(38). Similarly, a synergistic interplay between host and symbiont components mediates the initiation and persistence of the bobtail squid-Vibrio fischeri symbiosis (39)(40)(41).…”

Flavonoids in plant rhizospheres: secretion, fate and their effects on biological communication

“…The molecular mechanisms of bacterial and plant perception, signaling, organogenesis and nitrogen fixation have been intensively studied, with many components essential for these symbiotic interactions identified (Popp and Ott 2011;Wang et al 2012;Werner 2007;Yokota and Hayashi 2011). Due to the chemotaxis of rhizobia to root exudates, these rhizobia can find their host legume plants in soils.…”

Host-secreted antimicrobial peptide enforces symbiotic selectivity in Medicago truncatula

“…This symbiotic relationship is highly selective: Particular rhizobial species or strains establish an efficient symbiosis with only a limited set of legume species or genotypes (1,2). Such specificity can occur at different stages of symbiotic development, ranging from initial nodule primordium induction and bacterial infection (nodulation specificity) to late nodule development involving bacterial differentiation and symbiotic persistence (nitrogen fixation specificity) (2). A comprehensive understanding of the genetic mechanisms that control this specificity has important implications in agriculture because it allows for genetic manipulation of the host or bacterial symbionts to optimize the agronomic potential of biological nitrogen fixation.…”

“…For this reason, multiple genetic and molecular mechanisms could be involved in the regulation of compatibility in the legume-rhizobial interactions (1,2). In most legumes, nodule morphogenesis and bacterial infection is mediated by host-specific recognition of rhizobial lipo-chitooligosaccharides known as nodulation (Nod) factors.…”