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CRISPR Gene Editing

Clustered regularly interspersed short palindromic repeats, or CRISPR, and the CRISPR-associated protein, Cas, together form a type of microbial immune system that causes targeted DNA breaks in viruses that infect bacteria.

In 2012 Jennifer Doudna and Emmanuelle Charpentier realised that they could re-engineer this system to target any gene and in any organism. This had profound consequences for agriculture, and almost overnight plant breeders were provided with a tool that could safely produce new varieties of crops with improved agronomic traits and consumer appeal. This could be done more precisely, cheaply, more easily and faster than any method of crop development that had existed before, namely cross-pollination, hybridisation, induced mutation or genetic modification.

Mutations sometimes arise spontaneously. They may be caused by sunshine, exposure to certain chemicals, or simply a mistake that gets made during the copying of genetic material. This slight bumbling of DNA replication over long periods of time is the process that eventually provided us with the crops we farm today – things that are now fundamentally different from their wild ancestors and better suited to grow according to man’s needs. Whenever a mutation occurs it may slightly change the way a plant grows.

Sometimes this causes plants to grow faster, or to be easier to harvest. Early farmers therefore used those plants with desirable traits as breeding stock to produce the next generation, which enriched those desirable genes’ presence in the gene pool. In the 1930s researchers realised that they could use DNA damaging chemicals or ionising radiation to accelerate the rate of mutation with a technique called induced mutation. The DNA from plants developed by this technique is indistinguishable from those that were developed by the older method, and so they are considered to be perfectly safe to eat.

Some 3 300 varieties have so far been developed in this way for nearly every single species of cultivated plant. While this process is faster than its forerunner, it is not an easy process to implement and many hundreds of thousands of plants are subjected to the mutations, grown to maturity and then selected from there in the hope that something attractive may appear. However, it cannot be predicted where in the DNA, or what exactly this induced change may be. Plants edited with CRISPR-Cas carry these same types of mutation and are indistinguishable from those mutations that occur naturally or by induction. Gene editing is often thought of as a new breeding technique in its own right, but it is essentially just the next step in a system of plant breeding and selection that has existed for as long as agriculture has. Gene editing allows the mutations to be caused at very specific positions within the plant’s DNA and therefore eliminates the random nature of breeding and the need for large trials. An existing variety can simply be gene edited to ensure CRISPR GENE EDITING FOR CROP DEVELOPMENT

it carries a certain desired trait, rather than searching for it in a proverbial haystack after the random induction of mutations. CRISPR-Cas gene editing is more precise than any form of induced mutagenesis that has existed previously. It is more reliable, easier to use, more versatile in target site selection, and cheaper than other forms of gene editing that currently exist. In a process referred to as the democratisation of biotech, the formerly restrictive field of plant breeding and variety development has been opened to anyone with a decent understanding of molecular biology.

The system has two components: CRISPR functions as a guiding mechanism to shuttle Cas along to specific DNA regions. Once there, Cas cuts through both strands of the DNA. After the break has been made, the cell’s DNA repair machinery begins to function. The repair process is error prone and will randomly insert or delete DNA bases during the reconnection of broken ends, which generally has the effect of inactivating the gene in question. This targeted method of DNA cleavage allows for specific genes to be inactivated in a way that is indistinguishable from naturally occurring mutations.

Using CRISPR to develop new agricultural varieties is very appealing when it is considered how cheaply and easily it can be implemented. Almost all that is needed is a good knowledge of which genes cause which undesirable traits and what their DNA sequence is. These can then be silenced and the resulting plant should be free of that trait. Fungus-resistant wheat, higher-yielding rice, late-flowering and bigger soybeans, albino watermelons, disease-resistant citrus, and more easily harvestable tomatoes are but a few types of plants that have already been developed with this method of genome editing.

As this process does not require foreign DNA to be inserted or integrated into the new variety, the developed plants are not considered to be GMOs, but are rather treated as conventionally bred plants. They do not require to be specially labelled and have avoided the lengthy and burdensome compliance with GMO legislation, although this does depend on the laws of the country in question. The arrival and widespread applicability of CRISPR is an unprecedented leap in agricultural technology, and it holds great promise to make an even bigger advance than the Green Revolution of the sixties did. It would be unwise to pay heed to arguments from a position of ignorance that the technology should be regulated and to make the same mistake that we did with excessive legislation around genetic modification in the 90s.

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