Abstract
Previously we reported that ferrous Fe transporters in rice, OsIRT1 and OsIRT2, take up Cd (Nakanishi et al., 2006). Furthermore, overexpression of OsIRT1 increased Cd accumulation in rice (Lee and An, 2009). We investigated the role of OsNRAMP1, an Fe transporter, in Cd uptake and transport in rice.
OsNRAMP1::GFP fusion proteins localised to the plasma membrane in onion epidermal cells. The growth of yeast expressing OsNRAMP1 was impaired in the presence of Cd compared to yeast transformed with empty vector. Moreover, the Cd content of the OsNRAMP1-expressing yeast exceeded that of the vector control. Overexpression of OsNRAMP1 in rice increased Cd accumulation in the leaves.
The expression of OsNRAMP1 in the roots was higher in a high Cd-accumulating cultivar (Habataki) compared to a low Cd-accumulating cultivar (Sasanishiki) irrespective of the presence of Cd, and the amino acid sequence of OsNRAMP1 showed 100% identity between Sasanishiki and Habataki. These results suggest that OsNRAMP1 participates in cellular Cd uptake and Cd transport within rice, and the higher expression of OsNRAMP1 in the roots could lead to the increase of Cd accumulation in the shoots.
