The Ammonium Transporter SpAMT1;2 Contributes to Nitrogen Utilisation and Cadmium Accumulation in the Hyperaccumulator Sedum Plumbizincicola.

Sedum plumbizincicola (Sp) is a cadmium (Cd) hyperaccumulator found specifically in abandoned ancient mines where N is regularly deficient while Cd presents in excess. How Sp got adapted to this unique habitat remains unknown. Here, we reported relative abundant presence of NH in mine areas for Sp, and the isolation and functional characterisation of a putative NH transporter gene AMT1;2, which is highly expressed in Sp roots and encodes a pH-dependent dual affinity ammonium uptake transporter. Compared to SaAMT1;2, the homologous gene in the nonhyperaccumulating control Sedum alfredii (Sa), SpAMT1;2 expression is much higher and not inhibited by Cd. Only eight amino acid sequence polymorphisms were observed between SpAMT1;2 and SaAMT1;2, and the in-vitro NH uptake activity and subcellular localisation are identical between them with or without Cd stress. Moreover, in contrast in Sa, NH uptake in Sp is not inhibited by Cd, and NH at ambient level promotes Cd accumulation. These data suggest that SpAMT1;2 is likely an essential gene contributing to nitrogen nutrition and the interaction between NH and Cd uptake in Sp, which might represent a novel N utilisation pathway evolved in mines for the hyperaccumulator Sp.