An Iron Uptake Operon Required for Proper Nodule Development in the Bradyrhizobium japonicum-Soybean Symbiosis

• DOI: 10.1094/mpmi-18-0950
• Publication Date: 2007-05-11T09:37:36Z
• Authors: Heather P. Benson; Eric Boncompagni; Mary Lou Guerinot
• Keywords: Bradyrhizobium japonicum; Ferrichrome; Leghemoglobin; Bradyrhizobium; Sinorhizobium meliloti

Rhizobia live in the soil or enter into a nitrogen-fixing symbiosis with suitable host plant. Each environment presents different challenges respect to iron acquisition. The soybean symbiont Bradyrhizobium japonicum 61A152 can utilize variety of siderophores (Fe[III]-specific ligands). Purification iron-regulated outer membrane proteins had previously allowed cloning gene, fegA, from B. ja-ponicum 61A152, whose predicted protein shares significant amino acid similarity known TonB-dependent siderophore receptors. Here, we show that fegA is an operon fegB, encode inner protein. Characterization fegAB and fegB mutants shows both are required for utilization ferrichrome. Whereas mutant forms normal symbiosis, has dramatic phenotype planta. Six weeks after inoculation strain, nodules do not contain leghemoglobin fix nitrogen. Infected cells few symbiosomes filled vesicles. As ferrichrome fungal likely be available nodules, symbiotic defect suggests serving function planta, possibly one involved signaling between two partners.