The nitrate transporter family protein LjNPF8.6 controls the N-fixing nodule activity

N-fixing nodules are new organs formed on legume roots as result of the beneficial interaction with soil bacteria, rhizobia. The nodule functioning is still a poorly characterized step of the symbiotic interaction as only few of the genes induced in N-fixing nodules have been functionally characterized. We present here the characterization of the member of the Lotus japonicus nitrate transporter 1/peptide transporter family LjNPF8.6. The phenotypic characterization carried out in independent L. japonicus LORE1 insertion lines indicates a positive role of LjNPF8.6 on nodule functioning as knock out mutants display N-fixation deficiency (25%) and increased nodular superoxide content. The partially compromised nodule functioning induces two striking phenotypes: anthocyanin accumulation already displayed four weeks after inoculation and shoot biomass deficiency, which is detected by long-term phenotyping. LjNPF8.6 achieves nitrate uptake in Xenopus laevis oocytes both at 0.5 mM and 30 mM external concentrations and a possible role as nitrate transporter on the control of N-fixing nodule activity is discussed