Abstract
Aluminum (Al) is the most abundant metal in the Earth's crust, but its trivalent ionic form is highly toxic to all organisms at low concentrations. How Al enters cells has not been elucidated in any organisms. Herein, we report a transporter, Nrat1 (Nramp aluminum transporter 1), specific for trivalent Al ion in rice. Nrat1 belongs to the Nramp (natural resistance-associated macrophage protein) family, but shares a low similarity with other Nramp members. When expressed in yeast, Nrat1 transports trivalent Al ion, but not other divalent ions such as manganese, iron and cadmium, or the Al-citrate complex. Nrat1 is localized at the plasma membranes of all cells of root tips. Knockout of Nrat1 resulted in decreased Al uptake and increased sensitivity to Al, but the tolerance to other metals was not altered. One the other hand, over-expression of Nrat1 led to enhanced Al uptake in rice roots. Expression of Nrat1 is up-regulated by Al in the roots and regulated by a C2H2 zinc transcription factor (ART1). Our results indicate that Nrat1 is a transporter specific for trivalent Al, which is involved in Al tolerance in rice.
