A member of the Phosphate transporter 1 (Pht1) family from the arsenic-hyperaccumulating fern Pteris vittata is a high-affinity arsenate transporter

Abstract

Pteris vittata exhibits enhanced arsenic uptake, but the corresponding mechanisms are not well known. The prevalent form of arsenic in most soils is arsenate, which is a phosphate analog and a substrate for Phosphate transporter 1 (Pht1) transporters. Herein we identify and characterize three P. vittata Pht1 transporters. Pteris vittata Pht1 cDNAs were isolated and characterized via heterologous expression in Saccharomyces cerevisiae (yeast) and Nicotiana benthamiana leaves. Expression of the PvPht1 loci in P. vittata gametophytes was also examined in response to phosphate deficiency and arsenate exposure. Expression of each of the PvPht1 cDNAs complemented the phosphate uptake defect of a yeast mutant. Compared with yeast cells expressing Arabidopsis thaliana Pht1;5, cells expressing PvPht1;3 were more sensitive to arsenate, and accumulated more arsenic. Uptake assays with yeast cells and radiolabeled 32P revealed that PvPht1;3 and AtPht1;5 have similar affinities for phosphate, but the affinity of PvPht1;3 for arsenate is much greater. In P. vittata gametophytes, PvPht1;3 transcript levels increased in response to phosphate (Pi) deficiency and arsenate exposure. PvPht1;3 is induced by Pi deficiency and arsenate, and encodes a phosphate transporter that has a high affinity for arsenate. PvPht1;3 probably contributes to the enhanced arsenate uptake capacity and affinity exhibited by P. vittata.