Abstract
-Iron (Fe) is an essential element, its transport is regulated by the cell redox balance. In seeds, Fe enters the embryo as Fe2+ and is stored in vacuoles as Fe3+ . Through its ferric reduction activity, ascorbate plays a major role in Fe redox state and hence Fe transport within the seed. -We have searched for ascorbate membrane transporters responsible for controlling Fe reduction through a screening in the yeast ferric reductase-deficient fre1 strain and have isolated AtDTX25, a member of the Multidrug And Toxic compound Extrusion (MATE) family. -AtDTX25 was shown to mediate ascorbate efflux when expressed in yeast and Xenopus oocytes, in a pH-dependent manner. In planta, AtDTX25 is highly expressed during germination and encodes a vacuolar membrane protein. Isolated vacuoles from AtDTX25-1 knockout mutant contained less ascorbate and more Fe than WT and mutant seedlings were highly sensitive to Fe deficiency. Iron imaging further showed that the remobilization of Fe from vacuoles was highly impaired in mutant seedlings. -Taken together, our results establish AtDTX25 as a vacuolar ascorbate transporter, required during germination to promote reduction of the pool of stored Fe3+ and its remobilization to feed the developing seedling.