Abstract
Upon recognizing flavonoids excreted from the leguminous plants, Rhizobium produces Nod factor (lipochitin-oligosaccharides) that acts as developmental and infectious signals, eliciting nodulation and successful infection in the roots of leguminous hosts. From EMS mutagenesis using the model legume Lotus japonicus, my collaborators and I have identified 12 loci required for initial stages of nodulation. Interestingly, among these mutants, sym71 (castor), sym72, sym82, sym84, sym85, sym86 (pollux), sym87 mutants were also unable to establish a symbiotic association with arbuscule mycorrhizal fungi, indicating the presence of a common signaling pathway consisting of at least 7 loci required for nodulation and mycorrhization. Root hairs exposed to Nod facotor display calcium oscillation in the cytoplasmic space near nuclei. Some of the mutants deficient in nodulation and mycorrhization fail to display this oscillation. Analysis of calcium oscillations in the mutants enables to divide symbiotic loci into upstream and downstream of the common signaling pathway.
