The latest apple out of the orchard, the Arctic apple, just so happens to resist the ugly browning kids reject if sliced. So, how does biotech factor into the equation? Genetic engineering.
This first-of-its-kind apple, approved by the USDA last week, caught our eye here at WEEKLY because it represents a new type of genetically modified food—one that has been engineered to directly appeal to and benefit the consumer, rather than the farmer. Because of the newer technology used in the creation of the fruit, lingering safety concerns voiced by critics may begin to fade.
Let’s take a look at how biotechnology silences the apple browning gene and visit its application in the field of genetically modified food.
Why so Brown?
The browning observed in conventional apples is the end result of an oxidation reaction. The reaction is first catalyzed by an enzyme called “polyphenol oxidase” (PPO), which acts on a class of compounds called phenolic compounds, present in various fruits. In order for the reaction to occur, PPO has to come into contact with its substrate—the phenolic compounds. These compounds are typically sequestered inside of vacuoles, or internal compartments of a cell, which are enclosed by a membrane and filled with water.
If the cell is disrupted by slicing or dropping, the vacuoles burst and allow the phenolic compounds to come into contact with PPO, resulting in the brown tinge.
TURN THE BROWN UPSIDE DOWN
Okanagan Specialty Fruits (Summerland, B.C., Canada), the maker of the Arctic apple, sought to halt the oxidation of phenolic compounds. They chose to tackle the problem by blocking the production of the PPO protein; no enzyme, no chemical reaction, no brown. How? By using a gene silencing technique known as RNAi.
Recall from high school biology that RNA is single-stranded (ssRNA) and is the set of instructions from the gene to the ribosome to make protein. RNAi technology creates a double-stranded RNA (dsRNA) by introducing an RNA sequence into a cell which is complementary to the RNA for the particular gene to be silenced. When both ssRNAs meet, dsRNA is formed. The cell recognizes dsRNA as “foreign” and destroys it.
Short segments of apple DNA, coding for the four different PPO genes, were transferred to make the Arctic apple. Once expressed, the short segments of DNA produce a segment of RNA complementary to the PPO RNA already being made by the apple. The resulting dsRNA is immediately destroyed by the cell. No PPO equates to Arctic apples’ “just sliced” appearance.
In the Industry
All facets of the industry, such as the growers, packers, shippers, and retailers will benefit from the stoppage of the oxidation process. Food processors, likewise, will be able to produce more consistent juices, sauces, and sliced apple products without relying on antioxidant treatments currently in use.
The technology also allows for better discernment between simple bruising and a rotten apple. With oxidation no longer an issue, brown discolorations on an apple will more likely indicate rot, meaning more sellable product and less waste.
To the Market
Since Arctic apples contain no foreign DNA (the 4 introduced genes are apple DNA), they are likely to impart a truer flavor to GMO wary consumers. Having undergone ten years of field testing, Arctic apples do not differ in any significant respect to unmodified apples, apart from the lack of PPO enzyme.
The USDA approval grants permission to market the plants to growers, so the first two varieties of modified apples, Golden Delicious and Granny Smith, will be available in Fall of 2016. If the Arctic apples are successful, they could pave the way for other consumer oriented products, such as oxidation-resistant cherries and pears, which are in development at Okanagan Specialty Fruits.
A similar product, the Innate Potato, was approved last November by the USDA. Developed by J.R. Simplot (Boise, Idaho), the spud also uses RNAi technology to decrease production of the PPO protein in order to reduce browning.
The production of a second protein in Innate potatoes, asparagine synthetase-1, is also knocked down using the same technology. When potatoes are cooked at high temperatures, asparagine synthetase-1 reacts with the potato sugars to produce a chemical called acrylamide which has been linked to cancer in rodents. Simplot plans to launch the potato in limited test markets during spring of 2015.
Emily Burke, PhD has worked in biopharma for 20 years, gaining science writing experience at The Scripps Research Institute and Ionis Pharmaceuticals. As a Ph.D. molecular biologist, she is passionate about advancing the public’s understanding of science. In addition to being a self-proclaimed “science geek,” she is regularly asked to speak at international scientific meetings. When not teaching and writing the WEEKLY for Biotech Primer, Dr. Burke swims with her swim club and performs regularly on the improv circuit in San Diego.