Rhizobium leguminosarum bv. trifolii NodD2 Enhances Competitive Nodule Colonization in the Clover-Rhizobium Symbiosis

Establishment of the rhizobium-legume symbiosis requires a highly specific and complex signal exchange between both participants. Rhizobia perceive legume flavonoid compounds through LysR-type NodD regulators. Often, rhizobia encode multiple copies of nodD , which is one determinant of host specificity. In some species of rhizobia, the presence of multiple copies of NodD extends their symbiotic host-range. Here, we identified and characterized a second copy of nodD present in some strains of the clover microsymbiont Rhizobium leguminosarum bv. trifolii. The second nodD gene contributed to the competitive ability of the strain on white clover, an important forage legume. A screen for strains containing nodD2 could be utilized as one criterion to select strains with enhanced competitive ability for use as inoculants for pasture production.