Fig. 8: Proposed model of NIGT1-NRAMP2 regulatory module in soybean nodules.

Fe is unloaded from nodule vasculature to infected cells by apoplastic (a) and symplastic (b) approaches. GmNRAMP2a&2b are both Fe influx transporters localized at the tonoplast of uninfected tissues, and they facilitate Fe transfer to infected cells. Under inorganic N-sufficient conditions, the expression of GmNRAMP2a&2b is suppressed by a pair of N-signal regulators GmNIGT1a&1b in uninfected tissues, and thus blocks Fe transfer for SNF. GmVTL1a facilitates Fe transport into symbiosomes for SNF21.