title: Elevated nicotianamine levels in Arabidopsis halleri roots play a key role in zinc hyperaccumulation.
abstract: Zn deficiency is among the leading health risk factors in developing countries. Breeding of Zn-enriched crops is expected to be facilitated by molecular dissection of plant Zn hyperaccumulation (i.e., the ability of certain plants to accumulate Zn to levels >100-fold higher than normal plants). The model hyperaccumulators Arabidopsis halleri and Noccaea caerulescens share elevated nicotianamine synthase (NAS) expression relative to nonaccumulators among a core of alterations in metal homeostasis. Suppression of Ah-NAS2 by RNA interference (RNAi) resulted in strongly reduced root nicotianamine (NA) accumulation and a concomitant decrease in root-to-shoot translocation of Zn. Speciation analysis by size-exclusion chromatography coupled to inductively coupled plasma mass spectrometry showed that the dominating Zn ligands in roots were NA and thiols. In NAS2-RNAi plants, a marked increase in Zn-thiol species was observed. Wild-type A. halleri plants cultivated on their native soil showed elemental profiles very similar to those found in field samples. Leaf Zn concentrations in NAS2-RNAi lines, however, did not reach the Zn hyperaccumulation threshold. Leaf Cd accumulation was also significantly reduced. These results demonstrate a role for NAS2 in Zn hyperaccumulation also under near-natural conditions. We propose that NA forms complexes with Zn(II) in root cells and facilitates symplastic passage of Zn(II) toward the xylem.
authors.affiliation: Department of Plant Physiology, University of Bayreuth, 95440 Bayreuth, Germany.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Deinlein
authors.forename: Michael
authors.initials: M
authors.lastname: Weber
authors.forename: Holger
authors.initials: H
authors.lastname: Schmidt
authors.forename: Stefan
authors.initials: S
authors.lastname: Rensch
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Trampczynska
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Hansen
authors.forename: Søren
authors.initials: S
authors.lastname: Husted
authors.forename: Jan K
authors.initials: JK
authors.lastname: Schjoerring
authors.forename: Ina N
authors.initials: IN
authors.lastname: Talke
authors.forename: Ute
authors.initials: U
authors.lastname: Krämer
authors.forename: Stephan
authors.initials: S
authors.lastname: Clemens
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001383:Azetidinecarboxylic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D055785:Gene Knockdown Techniques; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000201:enzymology / Q000235:genetics; D034622:RNA Interference; D012987:Soil / Q000032:analysis; D015032:Zinc / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D012987:Soil; C082893:nicotianamine; D001383:Azetidinecarboxylic Acid; D019883:Alkyl and Aryl Transferases; C118230:nicotianamine synthase; D015032:Zinc