GmVTL1 is an iron transporter on the symbiosome membrane of soybean with an important role in nitrogen fixation.

Abstract

O_LILegumes establish symbiotic relationships with soil bacteria (rhizobia), housed in nodules on plant roots. The plant supplies carbon substrates and other nutrients to the bacteria in exchange for fixed nitrogen. The exchange occurs across a plant-derived symbiosome membrane (SM), which encloses rhizobia to form a symbiosome. Iron supplied by the plant is crucial for the rhizobial enzyme nitrogenase that catalyses N2 fixation, but the SM iron transporter has not been identified. C_LIO_LIWe use complementation of yeast and plant mutants, real-time PCR, hairy root transformation, microscopy and proteomics to demonstrate the role of soybean GmVTL1 and 2. C_LIO_LIBoth are members of the vacuolar iron transporter family and homologous to Lotus japonicus SEN1 (LjSEN1), previously shown to be essential for N2 fixation. GmVTL1 expression is enhanced in nodule infected cells and both proteins are localised to the SM. C_LIO_LIGmVTL1 and 2 transport iron in yeast and GmVTL1 restores N2 fixation when expressed in the Ljsen1 mutant. C_LIO_LIThree GmVTL1 amino acid substitutions that reduce iron transport in yeast also block N2 fixation in Ljsen1 plants. C_LIO_LIWe conclude GmVTL1 is responsible for transport of iron across the SM to bacteroids and plays a crucial role in the N2-fixing symbiosis. C_LI