Metallothionein expression in chloroplasts enhances mercury accumulation and phytoremediation capability
Article first published online: 24 APR 2011
© 2011 The Authors. Plant Biotechnology Journal © 2011 Society for Experimental Biology, Association of Applied Biologists and Blackwell Publishing Ltd
Plant Biotechnology Journal
Special Issue: Chloroplast Biotechnology
Volume 9, Issue 5, pages 609–617, June 2011
How to Cite
Ruiz, O. N., Alvarez, D., Torres, C., Roman, L. and Daniell, H. (2011), Metallothionein expression in chloroplasts enhances mercury accumulation and phytoremediation capability. Plant Biotechnology Journal, 9: 609–617. doi: 10.1111/j.1467-7652.2011.00616.x
- Issue published online: 6 MAY 2011
- Article first published online: 24 APR 2011
- Received 31 October 2010; revised 24 January 2011; accepted 28 January 2011.
- plastid genome;
- real-time PCR;
- genetic engineering;
- environmental biotechnology
Genetic engineering to enhance mercury phytoremediation has been accomplished by expression of the merAB genes that protects the cell by converting Hg[II] into Hg which volatilizes from the cell. A drawback of this approach is that toxic Hg is released back into the environment. A better phytoremediation strategy would be to accumulate mercury inside plants for subsequent retrieval. We report here the development of a transplastomic approach to express the mouse metallothionein gene (mt1) and accumulate mercury in high concentrations within plant cells. Real-time PCR analysis showed that up to 1284 copies of the mt1 gene were found per cell when compared with 1326 copies of the 16S rrn gene, thereby attaining homoplasmy. Past studies in chloroplast transformation used qualitative Southern blots to evaluate indirectly transgene copy number, whereas we used real-time PCR for the first time to establish homoplasmy and estimate transgene copy number and transcript levels. The mt1 transcript levels were very high with 183 000 copies per ng of RNA or 41% the abundance of the 16S rrn transcripts. The transplastomic lines were resistant up to 20 μm mercury and maintained high chlorophyll content and biomass. Although the transgenic plants accumulated high concentrations of mercury in all tissues, leaves accumulated up to 106 ng, indicating active phytoremediation and translocation of mercury. Such accumulation of mercury in plant tissues facilitates proper disposal or recycling. This study reports, for the first time, the use of metallothioniens in plants for mercury phytoremediation. Chloroplast genetic engineering approach is useful to express metal-scavenging proteins for phytoremediation.