The Agreeable Face of Genome Editing
Plant breeders rely on genetic variation in order to create crop varieties that are adapted to different environments. Since the earliest days of organised agriculture, farmers have selected the best performing individual plants and propagated them, mainly through seed. Selecting the outliers in a population of plants has proven to be a cornerstone of plant breeding throughout the millennia. Observant farmers were selecting long before we knew what the hereditary material was (DNA) and even how the “the hereditary principle”, studied by Mendel in 1866 was organised. Describing chromosomes came even later (von Waldeyer-Hartz, 1888, Boveri and Sutton, 1902).
If genomes were invariant, breeders would have little work to do. Without genetic variation it would be impossible to use genetics to improve crop performance unless we had special tools that allowed us to intervene in the basic structure of the genome.
Fortunately, genetic variation is widespread and continuous. The process of sexual reproduction allows for major chromosomal rearrangements to occur during meiosis needed for sexual reproduction. However, the DNA of all organisms is continuously altered by the effects of unavoidable environmental influences, which cause mutations in DNA. These include cosmic rays, natural radioactivity, natural and man-made chemicals and even simple “mistakes” in DNA replication. Add to this “horizontal” gene transfer, where organisms can share their DNA with sexually-incompatible species, to create novel traits in the recipient organism. When plant breeders discover that there is insufficient genetic variation in the crop on which they work, they generate variation by increasing the natural mutation rate using ionizing radiation or chemical treatments. The majority of our plant breeding germplasm has at some time undergone such mutagenic interventions in order to give breeders more phenotypic variation from which they can select superior performance.
In the last 30 years there has been a series of scientific breakthroughs, which have allowed us to produce targeted and predicted variation in crops. In the 1980s, the first examples of gene transfer into plants to produce transgenics emerged. These enabled the development of truly novel traits in important crops. This technique has been widely adopted in major field crops including corn, soybeans, canola, cotton, papaya, sugar beet and several others. However, it has not been without controversy and transgenic crops (GM-crops) are still not grown widely in many countries, including most of the EU.
More recently, there has been the development of a very versatile, yet subtle technique for creating predictable variation. It has been named “genome editing”. This technique is a precisely targeted way to change DNA at a base-by-base level. There are several ways to perform genome editing, but a system called CRISPR-cas9 has made this process so easy that even high-school students can incorporate it into science-fair projects. The most interesting thing about genome editing is that it only replicates what could happen naturally through mutation or through routine (and permitted) interventions used by breeders to enhance genetic variation. Because genome editing is so targeted, it rarely leads to unknown or unexpected changes, whereas natural mutations or those produced by breeders are always accompanied by a large amount of additional mutations (mutational baggage) that are never mapped or analysed.
Over the past few years, there have been three instances of genome-edited food products (in corn, in mushrooms and potatoes), where the USDA has decided that the edited product should not be regulated by USDA on the grounds that the same product could have occurred naturally or using unregulated techniques commonly used in plant breeding.
Against this background, the U.S. Secretary of Agriculture, Sonny Perdue, issued a statement on March 28th providing clarification on the U.S. Department of Agriculture’s (USDA) oversight of plants produced through new breeding technologies, which include genome editing.
This statement is an unequivocal endorsement of genome editing as a safe and effective tool for plant breeders to adopt in order to generate new varieties of crops with superior performance and better nutritional quality. It was a very welcome statement of support for continued innovation in agriculture at a time when the issue of global food security is becoming more evident to policymakers and the general population.
The EU, which has been very cautious about embracing the cultivation of GM crops (despite importing large quantities of GM soybeans), is undergoing a drawn-out consultation and debate on the nature of genome editing. The decision as to how genome editing will be handled has been postponed several times by the Commission. However, the Advocate General of the Court of Justice of the European Union recently published a legal opinion which clearly excludes genome editing from the EU laws covering GM crops. As an opinion, it is not binding on the EU member states, but it does indicate a level of scientific rationality in the judiciary that seems to be absent in the law-makers. However, a move by the EU commission towards something closer to Secretary Perdue’s statement would have a profound, positive impact on innovation in food and agriculture, food security and trading in agricultural products.
We can only live in hope, and encourage unity around the use of this important technology for better crops and improved nutrition worldwide.