title: Knocking out ACR2 does not affect arsenic redox status in Arabidopsis thaliana: implications for as detoxification and accumulation in plants.
abstract: Many plant species are able to reduce arsenate to arsenite efficiently, which is an important step allowing detoxification of As through either efflux of arsenite or complexation with thiol compounds. It has been suggested that this reduction is catalyzed by ACR2, a plant homologue of the yeast arsenate reductase ScACR2. Silencing of AtACR2 was reported to result in As hyperaccumulation in the shoots of Arabidopsis thaliana. However, no information of the in vivo As speciation has been reported. Here, we investigated the effect of AtACR2 knockout or overexpression on As speciation, arsenite efflux from roots and As accumulation in shoots. T-DNA insertion lines, overexpression lines and wild-type (WT) plants were exposed to different concentrations of arsenate for different periods, and As speciation in plants and arsenite efflux were determined using HPLC-ICP-MS. There were no significant differences in As speciation between different lines, with arsenite accounting for >90% of the total extractable As in both roots and shoots. Arsenite efflux to the external medium represented on average 77% of the arsenate taken up during 6 h exposure, but there were no significant differences between WT and mutants or overexpression lines. Accumulation of As in the shoots was also unaffected by AtACR2 knockout or overexpression. Additionally, after exposure to arsenate, the yeast (Saccharomyces cerevisiae) strain with ScACR2 deleted showed similar As speciation as the WT with arsenite-thiol complexes being the predominant species. Our results suggest the existence of multiple pathways of arsenate reduction in plants and yeast.
authors.affiliation: Rothamsted Research, Harpenden, Hertfordshire, United Kingdom.
authors.forename: Wenju
authors.initials: W
authors.lastname: Liu
authors.forename: Henk
authors.initials: H
authors.lastname: Schat
authors.forename: Mathijs
authors.initials: M
authors.lastname: Bliek
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.forename: Steve P
authors.initials: SP
authors.lastname: McGrath
authors.forename: Graham
authors.initials: G
authors.lastname: George
authors.forename: David E
authors.initials: DE
authors.lastname: Salt
authors.forename: Fang-Jie
authors.initials: FJ
authors.lastname: Zhao
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D029681:Arabidopsis Proteins / Q000235:genetics*; D001149:Arsenates / Q000378:metabolism / Q000633:toxicity; D001151:Arsenic / Q000378:metabolism*; D018053:Arsenites / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D055786:Gene Knockout Techniques; D008658:Inactivation, Metabolic; D009097:Multienzyme Complexes / Q000235:genetics*; D016254:Mutagenesis, Insertional / Q000187:drug effects / Q000235:genetics; D009154:Mutation / Q000235:genetics; D010084:Oxidation-Reduction / Q000187:drug effects; D010088:Oxidoreductases / Q000235:genetics*; D010710:Phosphates / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000378:metabolism; D013997:Time Factors; D056928:X-Ray Absorption Spectroscopy; D020687:cdc25 Phosphatases / Q000235:genetics*
chemical_list: D029681:Arabidopsis Proteins; D001149:Arsenates; D018053:Arsenites; D004269:DNA, Bacterial; D009097:Multienzyme Complexes; D010710:Phosphates; C036483:T-DNA; D010088:Oxidoreductases; C510678:arsenate reductase 2, Arabidopsis; D020687:cdc25 Phosphatases; C015001:arsenite; D001151:Arsenic; C025657:arsenic acid