Phytoremediation and Sequestration of Soil Metals Using the CRISPR/Cas9 Technology to Modify Plants: a Review

Soil contamination by toxic metals is a major health issue that could be partly solved by using genetically-modified plants. For that, the recently developed technique of clustered regularly interspaced short palindromic repeats (CRISPR) has created a new dimension in genetic engineering. CRISPR was first found as a part of the adaptive immune system in bacteria and archaea, and further refined to generate targeted breaks in DNA in a broad range of organisms. Various DNA changes can take place during the cellular repair process. Many plants, including crops, have the potential to tolerate, stabilize, and transform both organic and metal contaminants and have been already modified using the CRISPR method. Furthermore, many genes necessary to increase the absorption and tolerance of metals have been identified. Thus, using CRISPR, target genes could be activated or repressed to optimize phytoremediation in plants. Here we review the CRISPR/Cas9 technology applied to phytoremediation and sequestration of metals in the soil environment. The availability of the genome sequence plays a critical role in the adaptation of the CRISPR-mediated genome editing to specific plants. CRISPR has demonstrated outstanding potential for genome editing. However, the outcome depends on the selected target site, Cas9/Cpf1 function, gRNA design, delivery systems, and the off-target effects that may restrict its efficacy.