A novel plasma membrane-based NRAMP transporter contributes to Cd and Zn hyperaccumulation in Sedum alfredii Hance

Sedum alfredii is a native Chinese plant species that belongs to the group of metal hyperaccumulators and can accumulate significant amounts of Cd and Zn in the shoot without detrimental effects on its growth and metabolism. Understanding the molecular basis of this process may be essential for both phytoremediation of contaminated soils and developing heavy metal-resistant crop species. In this work, we have focused on NRAMP (Natural Resistance-Associated Macrophage Protein) family proteins transporters as potential candidates conferring superior hyperaccumulating ability in this species and undertaken its functional characterization. The bioinformatic analysis showed that SaNRAMP1 from S. alfredii showed very low similarity to all the NRAMP proteins from Arabidopsis thaliana. SaNRAMP1 was highly expressed in the young tissues of the shoots of hyperaccumulating ecotype of S. alfredii. Fluorescence imaging and functional studies revealed that SaNRAMP1 was localized at the plasma membrane and could transport not only Cd and Mn but also Zn. The latter trait makes it rather different from most reported NRAMP transporters. Overexpressing of SaNRAMP1 in tobacco significantly increased Cd, Zn, Mn concentration in the shoot. Taken together, our data suggest that SaNRAMP1 is a novel NRAMP protein that plays a significant role in Cd and Zn accumulation in S. alfredii. The above findings may be essential for understanding the mechanisms of metal hyperaccumulation in plants and used to both improve heavy metal tolerance in cash crops and use the potential of hyperaccumulating species for phytoremediation purposes.