Heavy Metal Induced Gene Expression in Plants

Abstract

Elements such as Cd, Zn, Cu, Cr and Pb are known as heavy metals and can be released from many materials to the biosphere as a result of industrial and other human activities and can cause severe environmental pollution. High concentrations of these heavy metals in the soil have negative effects on the growth, development and crop yield. The remediation of these pollutants from the environment especially from the contaminated soil and water is an important task for environmentalists and agricultural scientists in order to make our precious soil and water resources clean and reusable for our agricultural industry and for safe human consumption. It is important to develope new and less expensive technologies to remediate contaminated areas and eliminate the potential deleterious effects of these contaminants which may pose serious problems to our food quality and health, if not addressed properly. Phytoremediation, an in situ remediation technique, could be one of the best approach through which toxic metals can be extracted from the polluted soils and waters and is considered as an environmentally sustainable and low-input approach for remediation of contaminated soils and waters. These techniques use the hyperaccumulator plants to remove toxic contaminants from the medium in situ (soil and/or water) and transport to the roots and accumulate them in their aerial parts which could be harvested and removed from the site. However, it is a relatively new technology and there are not many researches available in order to understand the molecular mechanism of uptake, transport and accumulation of the toxic metals/metalloids in the harvestable parts of the plants. Recent research has shown great advances in the understanding of key mechanisms that function in heavy metal detoxification, transport and accumulation in plants. For example; genes of metal transporters, metal ATPases, microRNAs involved in translocation and accumulation process have been identified and their role in metal accumulation is being elucidated to some extent. Brassicaceae is a family that contains many types of metal accumulators. Several members of this family such as Brassica nigra, Brassica juncea, Brassica napus, and some other accumulator species like Arabidopsis halleri and Noccaea caerulescens (formerly Thlaspi caerulescens) have attracted attention due to their huge capacity of accumulating Cd, Zn, Cu, Pb and some other toxic metals and metalloids in their roots and shoots. In fact they could be suitable candidates for phytoremediation. In the coming years, the high through-put sequences technology, RNA sequence analysis and genome editing technologies will help the molecular biologists, breeders and genetists to generate new genotypes which could be highly efficient in cleanup the polluted environment. Furthermore, genetic engineering of the chloroplast genome offers a new way to obtain high expression without the risk of transgenic pollen spreading. The aim of this review is to provide a close understanding of the molecular mechanisms of heavy metal induced plant stress response and tolerance based on the current findings related to molecular biology and biotechnology research.

Keywords: Phytoremediation, Brassica nigra, Brassica juncea, Metal transporters, Hyperaccumulator plants

DOI: 10.7176/JSTR/5-12-20