Functional analysis of zinc hyperaccumulation related genes of Noccaea (Thlaspi) caerulescens for phytoremediation purposes

Zinc (Zn) and cadmium (Cd) are toxic metals that can cause serious soil contamination when present in excess. Especially Cd exposure is a threat to human health. Plants can potentially be used to clean-up the Zn- and/or Cd-contaminated soils in a technology called “Phytoremediation”. Two major requirements for this technology are the availability of plants that are accumulating Zn/Cd to high levels in their leaves and that are producing high biomass. Noccaea caerulescens is a natural model Zn/Cd/Ni hyperaccumulator species that can accumulate up to 3% of Zn and 1% of Cd. Unfortunately it does not make a lot of biomass, and is thus unsuitable for phytoremediation. To overcome this limitation, higher biomass producing crops like tobacco can be genetically modified with genes from N. caerulescens to induce metal tolerance and hyperaccumulation. NcZNT1 and NcMTP1 are metal transporter genes in N. caerulescens. Zeshan Hassan has engineered tobacco to express both these genes, separately and in combination, to investigate their role in Zn, Cd accumulation and tolerance and to explore their potential in improving the phytoremediation capacity of plants. Transgenic tobacco lines were more tolerant to high Zn and Cd, leading to higher biomass compared to non-transformed controls, and they accumulated 2-4 fold higher Zn and 2-3.5 fold higher Cd when grown in artificial nutrient solution systems. More importantly they also did so when grown in soil collected from a metal-contaminated site. One of the conclusions of Zeshan Hassan’s PhD thesis is that both NcZNT1 and NcMTP1 genes are important for Zn and Cd tolerance and accumulation and that transgenic tobacco expressing these genes have enhanced phytoremediation capacity, which could lead to interesting future applications.