Further characterization of an aluminum influx transporter in rice

Nrat1 is a plasma membrane-localized aluminum transporter recently identified in rice, which is a member of Nramp family. Here, we further characterized this transporter in terms of transport substrate specificity. Heterologous assay in yeast showed that Al transport activity by Nrat1 was unaffected by the presence of high concentration of Ca, but significantly inhibited by trivalent ions including Yb and Ga, analogs of Al. Knockout of Nrat1 did not affect the uptake of Cd and Mn in rice. On the other hand, over expression of Nrat1 led to enhanced Al uptake by rice roots compared with wild-type rice, but did not affect Cd uptake. These results provide further evidence that unlike other Nramp members, Nrat1 is an influx transporter for trivalent Al ion.