Summary
This study investigated the mechanism of nicotianamine (NA) secretion in plants by comparing the zinc/cadmium (Zn/Cd) hyperaccumulator Arabidopsis halleri with Arabidopsis thaliana. NA, a key metal chelator, is secreted into the rhizosphere of A. halleri, but the transporter responsible for this efflux remains unidentified.
Transcriptome analysis, quantitative reverse transcription polymerase chain reaction, and NA efflux assays in oocytes were used to identify and characterize candidate transporters. Transgenic A. thaliana lines with altered EFFLUX TRANSPORTER OF NA 1 (ENA1) expression were generated to assess its physiological role. NA secretion and Zn uptake were quantified using UPLC-MS/MS and 67Zn labeling. Promoter–GUS fusion and in situ hybridization revealed spatial expression.
ENA1 was identified as a plasma membrane-localized NA exporter with higher expression in A. halleri and Zn-induced expression only in this species. In A. thaliana, overexpression of ENA1 enhanced NA secretion and reduced Zn accumulation and sensitivity, while knockdown of homologs suppressed NA efflux. These results support a functional role of ENA1 in NA export.
ENA1 mediates root-based NA secretion and may contribute to Zn tolerance in hyperaccumulators. Its species-specific regulation and localization suggest an adaptive mechanism for rhizosphere metal management. This discovery advances our understanding of plant metal homeostasis and provides a molecular basis for phytoremediation and biofortification strategies.
