Mercuric ion reduction and resistance in transgenic Arabidopsis thaliana plants expressing a modified bacterial merA gene

• Published in: Proceedings of the National Academy of Sciences - PNAS 1996-04, Vol.93 (8), p.3182-3187
• Main Authors: Rugh, C.L. (University of Georgia, Athens, GA.), Wilde, H.D, Stack, N.M, Thompson, D.M, Summers, A.O, Meagher, R.B
• Format: Article
• Language: English
• Subjects: ADN RECOMBINADO; ADN RECOMBINE; Amino Acid Sequence; Arabidopsis - genetics; Arabidopsis - metabolism; ARABIDOPSIS THALIANA; Bacteria; Base Sequence; Biochemistry; CATION; CATIONES; Chromosome Mapping; DNA, Recombinant - genetics; Drug Resistance - genetics; Environmental Pollutants - metabolism; Environmental Pollutants - toxicity; ESCHERICHIA COLI; Escherichia coli - enzymology; Escherichia coli - genetics; EXPRESION GENICA; EXPRESSION DES GENES; GASES; GAZ; GENE; GENES; Genes, Bacterial; Genetics; MERCURE; MERCURIO; Mercury - metabolism; Mercury - toxicity; METAL; METALES; Molecular Sequence Data; MUTACION; MUTACION INDUCIDA; MUTATION; MUTATION PROVOQUEE; Oxidation-Reduction; Oxidoreductases - genetics; Oxidoreductases - metabolism; OXIDORREDUCTASAS; OXYDOREDUCTASE; PLANTAS TRANSGENICAS; PLANTE TRANSGENIQUE; Plants, Genetically Modified; REDUCCION; REDUCTION; RESISTANCE AUX FACTEURS NUISIBLES; RESISTENCIA A AGENTES DANINOS; RNA, Messenger - genetics; RNA, Messenger - metabolism; TRANSFERENCIA DE GENES; TRANSFERT DE GENE
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.93.8.3182

With global heavy metal contamination increasing, plants that can process heavy metals might provide efficient and ecologically sound approaches to sequestration and removal. Mercuric ion reductase, MerA, converts toxic Hg2+ to the less toxic, relatively inert metallic mercury (Hg0). The bacterial merA sequence is rich in CpG dinucleotides and has a highly skewed codon usage, both of which are particularly unfavorable to efficient expression in plants. We constructed a mutagenized merA sequence, merApe9, modifying the flanking region and 9% of the coding region and placing this sequence under control of plant regulatory elements. Transgenic Arabidopsis thaliana seeds expressing merApe9 germinated, and these seedlings grew, flowered, and set seed on medium containing HgCl2 concentrations of 25-100 micromolar (5-20 ppm), levels toxic to several controls. Transgenic merApe9 seedlings evolved considerable amounts of Hg0 relative to control plants. The rate of mercury evolution and the level of resistance were proportional to the steady-state mRNA level, confirming that resistance was due to expression of the MerApe9 enzyme. Plants and bacteria expressing merApe9 were also resistant to toxic levels of Au3+. These and other data suggest that there are potentially viable molecular genetic approaches to the phytoremediation of metal ion pollution