Out-of-the-Box: Science-Based Insights Into Food System Sustainability – Why Genome Editing Is So Remarkable
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By Paul Vincelli, University of Kentucky
Sunday, November 1, 2015
Why Genome Editing is So Remarkable
Genetic engineering of crops is undergoing a revolution, and it is being led by a new suite of techniques collectively called genome editing.
Genome editing takes advantage of two components: a natural bacterial enzyme that cuts DNA, and a “guide” molecule of RNA that matches the site in the plant’s DNA where the cut is to be made. Working together in a cell, these two components allow the biotechnologist to have much more control over the genetic changes taking place in the plant.
Although I am interested in how genome editing works, I am especially interested in how it differs from older methods of genetic engineering. Here are three key differences.
1. Genome editing can produce changes in precisely targeted genes. With older techniques of genetic engineering, one could insert specific and well-characterized genes into a plant. However, one had no control over where in the plant’s genetics the new gene landed…or how many copies were inserted. This was not a fatal limitation. However, the “collateral damage” to the plant’s genome from gene insertion requires that many plants must be engineered and thoroughly tested in hopes of finding a plant that performs as desired. But with genome editing, the biotechnologist can choose where and what kind of genetic change s/he wishes, resulting in much more control over the process of genetic engineering. This is a very big deal. Genome editing can still produce off-target changes in the plant’s genome, but its error rate is commonly quite low (Woo and colleagues, 2015). Furthermore, off-target effects of genome editing are considered comparable to those that occur through conventional breeding (EFSA, 2012). And as always in breeding, one tests the resulting plants to determine if any undesirable changes have occurred. In the case of genetic engineering, testing is extensive and includes molecular genetic analyses; analyses of chemical composition; evaluation for allergen production and for toxicity; testing in greenhouses, growth chambers, and the field; and other tests.
2. Genetic changes from genome editing sometimes cannot be distinguished from naturally occurring mutation. First, understand that mutations are quite natural and occur all the time in living organisms. In the case of genome editing, genetic changes can be as modest as a single-nucleotide change in a targeted gene. This is like changing one letter (a single typo) in a specific sentence in an entire book. A change of one nucleotide is the most precise and minimal change that is physically possible in a plant’s DNA. Such a change is so minimal that scientists simply cannot distinguish such a change from a mutation that occurred naturally. There would be no way to tell whether humans or Nature caused a genetic change of one nucleotide.
3. Genome editing can be done in ways that leave no trace of “foreign DNA” behind in the engineered plant. None. It can be impossible to tell that the plant was ever engineered. Thus, genome editing allows us to engineer plants in a minimally invasive and minimally disruptive way, leaving no trace of laboratory manipulation. For a recent example, see Woo and colleagues (2015). These authors never even used DNA in the genome-editing process.