ENA1, a transporter of nicotianamine that mediates secretion in the root of Arabidopsis

• Nicotianamine (NA), a key chelator in plant heavy metal homeostasis, plays a pivotal role in managing Zn bioavailability. In the Zn/Cd hyperaccumulator Arabidopsis halleri, NA is secreted into the rhizosphere, forming stable complexes with Zn to reduce its bioavailability and prevent rapid uptake. However, the NA transporter responsible for this secretion remains unidentified. • Transcriptome analysis of A. halleri and A. thaliana roots with further characterization led to the identification of EFFLUX TRANSPORTER OF NA1 (ENA1) as a plasma membrane-localized NA efflux transporter. ENA1 expression is significantly higher in A. halleri compared to A. thaliana and is induced by excess Zn only in A. halleri. • Increased ENA1 expression promotes NA secretion from roots into the rhizosphere without altering NA accumulation or long-distance root-to-shoot NA transport. Using 67Zn uptake experiments, we found that enhanced NA secretion alleviates Zn toxicity by reducing excess Zn uptake. • Promoter and in situ expression studies showed distinct root expression patterns of ENA1 between A. halleri and A. thaliana, aligning with the species-specific Zn detoxification strategies. • This discovery advances our understanding of Zn homeostasis mechanisms and provides a foundation for developing phytoremediation technologies to manage heavy metal contamination. RNA-Seq profilings of roots of hydroponic grown Arabidopsis halleri ssp. gemmifera and A. thaliana.