Introduction
Genetically modified crops on the market have gained a history of use as food for more than 20 years since the genetically modified tomato was first approved for commercialization.
While large-scale planting is currently carried out in major countries such as the United States, Brazil, Argentina, India, and Canada, most countries do not allow commercial cultivation of genetically modified crops because of the concern that foreign gene(s) inserted in such crops may have uncertain effects on the safety of the environment and/or human health. Therefore, genetically modified crops must pass strict safety risk assessments before being approved for marketing in various countries to ensure that they are safe and sound. With the continuous advancement of science, some emerging biotechnology can modify and improve crop characteristics without foreign gene insertion. Among them, gene-editing (genome editing) technology is one of the booming technologies in recent years.Gene-editing technology can be divided into two categories (Table 8.1): site-directed nucleases (SDNs), and the other is oligonucleotide-directed mutagenesis (ODM). Site-directed nucleases can further be divided into different types of techniques: meganuclease (MN), zinc finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and clustered regularly interspaced short palindromic repeat (CRISPR)-associated nuclease Cas9 (CRISPR-CasO).[487]
Site-directed nuclease technology can be divided into three categories depending on the cell’s gene repair mechanism and whether a template sequence is delivered: (1) SDN-1 produces a DNA double-stranded break, which is repaired via the cell non-homologous end joining (NHEJ) repair mechanism, resulting in deletion or insertion of one or a few base pairs. (2) SDN-2 produces a DNA double-stranded break, and at the same time, a homologous repair
Table 8.1 List of current gene-editing technology2
template is added.
The break is repaired via a cellular homologous recombination (homology-directed repair; HDR) repair mechanism using the template, where precise and small genetic modifications are generated. (3) SDN-3 produces a DNA double-stranded break. A DNA fragment with homologous ends in combination with non-homologous sequences is used as a template. The break is repaired using the template via a cellular HDR repair mechanism, resulting in the insertion of an exogenous gene at a specific location.Given that the debate over whether the gene-editing technology is equivalent to genetic modification technology and whether it can deviate from the regulatory mode of genetic modification technology, the regulatory approach to gene-edited food has not settled into a specific mode among various countries. Some countries regulate in accordance with the original regulatory model as GMOs, while others are still discussing possible different approaches.
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