title: Genome-wide association mapping identifies a new arsenate reductase enzyme critical for limiting arsenic accumulation in plants.
abstract: Inorganic arsenic is a carcinogen, and its ingestion through foods such as rice presents a significant risk to human health. Plants chemically reduce arsenate to arsenite. Using genome-wide association (GWA) mapping of loci controlling natural variation in arsenic accumulation in Arabidopsis thaliana allowed us to identify the arsenate reductase required for this reduction, which we named High Arsenic Content 1 (HAC1). Complementation verified the identity of HAC1, and expression in Escherichia coli lacking a functional arsenate reductase confirmed the arsenate reductase activity of HAC1. The HAC1 protein accumulates in the epidermis, the outer cell layer of the root, and also in the pericycle cells surrounding the central vascular tissue. Plants lacking HAC1 lose their ability to efflux arsenite from roots, leading to both increased transport of arsenic into the central vascular tissue and on into the shoot. HAC1 therefore functions to reduce arsenate to arsenite in the outer cell layer of the root, facilitating efflux of arsenic as arsenite back into the soil to limit both its accumulation in the root and transport to the shoot. Arsenate reduction by HAC1 in the pericycle may play a role in limiting arsenic loading into the xylem. Loss of HAC1-encoded arsenic reduction leads to a significant increase in arsenic accumulation in shoots, causing an increased sensitivity to arsenate toxicity. We also confirmed the previous observation that the ACR2 arsenate reductase in A. thaliana plays no detectable role in arsenic metabolism. Furthermore, ACR2 does not interact epistatically with HAC1, since arsenic metabolism in the acr2 hac1 double mutant is disrupted in an identical manner to that described for the hac1 single mutant. Our identification of HAC1 and its associated natural variation provides an important new resource for the development of low arsenic-containing food such as rice.
authors.affiliation: National Key Laboratory of Plant Molecular Genetics (NKLPMG), Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, United Kingdom.
authors.forename: Dai-Yin
authors.initials: DY
authors.lastname: Chao
authors.affiliation: Sustainable Soils and Grassland Systems Department, Rothamsted Research, Harpenden, Hertfordshire, United Kingdom.
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.affiliation: National Key Laboratory of Plant Molecular Genetics (NKLPMG), Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Jiugeng
authors.initials: J
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, China.
authors.forename: Shulin
authors.initials: S
authors.lastname: Shi
authors.affiliation: National Key Laboratory of Plant Molecular Genetics (NKLPMG), Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China; University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Ziru
authors.initials: Z
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, China.
authors.forename: Chengcheng
authors.initials: C
authors.lastname: Wang
authors.affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, United Kingdom.
authors.forename: John M
authors.initials: JM
authors.lastname: Danku
authors.affiliation: State Key Laboratory of Crop Genetics and Germplasm Enhancement, College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, China; Rothamsted Research, Harpenden, Hertfordshire, United Kingdom.
authors.forename: Fang-Jie
authors.initials: FJ
authors.lastname: Zhao
authors.affiliation: Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen, United Kingdom.
authors.forename: David E
authors.initials: DE
authors.lastname: Salt
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D053502:Arsenate Reductases / Q000235:genetics / Q000378:metabolism*; D001151:Arsenic / Q000378:metabolism*; D004843:Epistasis, Genetic; D017343:Genes, Plant; D056426:Genetic Loci; D055106:Genome-Wide Association Study; D008954:Models, Biological; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D018520:Plant Shoots / Q000378:metabolism; D015203:Reproducibility of Results; D020539:Sequence Analysis, Protein
chemical_list: D029681:Arabidopsis Proteins; D053502:Arsenate Reductases; D001151:Arsenic; C000599715:HAC1 (HIGH ARSENIC CONTENT 1) protein, Arabidopsis