The following is an excerpt of an article on Wired.com about the non-browning Arctic Apple.
The Arctic Apple, as it’s known, is strategically missing an enzyme so it doesn’t go brown when you take a bite and leave it sitting out on the counter. It’s one of the first foods engineered to appeal directly to the senses, rather than a farmer’s bottom line. And in a bid to attract consumers, it’s unapologetic about its alterations.
Neal Carter bought his first apple orchard in 1995, up in the gently sloping valley of Summerland, British Columbia. When he started, the future president of Okanagan Specialty Fruits didn’t have grand plans for upending the industry. But in his first few seasons he was struck by just how many apples (and how much money) he had to throw away on account of browning from the routine bumps and jostles of transit and packaging. Most years it was around 40 percent of his crop.
When you cut an apple, or handle it roughly, its cells rupture, and compounds that had been neatly compartmentalized come in contact with each other. When that happens, an enzyme called polyphenol oxidase, or PPO, triggers a chemical reaction that produces brown-colored melanin within just a few minutes. Carter thought there had to be a way to breed or engineer around that. So when he came across Australian researchers already doing it in potatoes, he wasted no time in licensing their technology, a technique known as gene silencing. Rather than knocking out a gene, the idea is to hijack the RNA instructions it sends out to make a protein.
The problem, Carter found out later, was that apples were a lot more complicated, genetically speaking, than the potato. In taters, the browning enzyme was coded into a family of four sub-genes that were chemically very similar. All you had to do was silence the dominant one, and it would cross-react with the other three, taking them all down in one go. Apples, on the other hand, had four families of PPO genes, none of which reacted with the others. So Carter’s team had to design a system to target all of them at once—no simple task in the early aughts.
To do it, the Okanagan scientists inserted a four-sequence apple gene (one for each member of the apple PPO family) whose base pairs run in reverse orientation to the native copies. To make sure it got expressed, they also attached some promoter regions taken from a cauliflower virus. The transgene’s RNA binds to the natural PPO-coding RNA, and the double-stranded sequence is read as a mistake and destroyed by the cell’s surveillance system. The result is a 90 percent reduction in the PPO enzyme. And without it, the apples don’t go brown.
To read the entire article, please visit Wired.