I am an Assistant Professor of tree fruit genomics at Cornell University. The goal of my research program is to understand the genetic and molecular mechanisms underlying important traits of apple so that efficient tools can be developed for genetic improvement. I am very interested in sharing the latest development in plant biotechnology with you, the readers of American/Western Fruit Grower. In this article, I would like to discuss the journey of Arctic Apples.
Arctic Apples are non-browning apples developed by a Canadian biotech company Okanagan Specialty Fruits (OSF) through genetic engineering (GE). They are commonly known as GMO apples. In February, the USDA’s Animal and Plant Health Inspection Service (APHIS) officially announced its decision to deregulate Arctic Golden Delicious and Arctic Granny Smith, the go-ahead for Arctic Apples to be grown and sold in the U.S.
Although GMO crops such as corn and soybeans have been grown in the U.S. since 1996 and APHIS had approved deregulation status for more than 180 GMO crop varieties before Arctic Apples were deregulated, the announcement regarding Arctic Apples has led to a heated debate on the fruit in both the U.S. and Canada.
The APHIS approval process took three years after the agency received OSF’s petition for deregulation in February 2012. During the approval process, APHIS offered two periods for public comments and received a total of 178,716 comments.
The major issues raised in these comments are potential negative impacts of Arctic Apples on the environment, human health, and conventional apple production and marketing.
The Review Process
It is fair to say that APHIS conducted an extensive and thorough review of the petition by addressing these issues. This could be evidenced from several important reports generated in assessing the petition, which are publicly available online.
After examining the data and facts presented in the petition, APHIS concluded that these issues were raised due to a distrust of GMO in general and/or an incomplete understanding of Arctic Apples.
Below is a brief description of several important facts about Arctic Apples that APHIS has considered in its decision. I hope it is helpful for you to understand why APHIS has approved Arctic Apples.
Background On Genomics
Most apples turn brown quickly if sliced or bitten. This browning process is a reaction that converts colorless phenols into pigmented quinones (in polymerized form). The key enzyme that controls the reaction is called polyphenol oxidase (PPO). To prevent fruit from browning, reducing the activity of PPOs is a direct and effective approach. In fact, this was exactly what OSF accomplished in developing Arctic Apples through GE.
In the apple genome, there are four distinct groups of PPO encoding genes consisting of 10 members in total. The representatives of the four groups of genes are PPO2, GPO3, APO5 and pSR7, or simply PGAS.
One of the common means in biotechnology for lowering the activity of a specific enzyme is to limit its protein (enzymes are proteins) translation from mRNA by making mRNA less available, a process called RNA interfering (RNAi). Many RNAi techniques have been developed to suppress genes of interest, including co-suppression, a technique that OSF employed to develop Arctic Apples.
The technical process of co-suppression is quite complex. I therefore will not describe it here. However, the important points to know are that OSF inserted two genes into the apple genome in this process.
The first is the transgene called PGAS that is, in fact, a hybrid gene partially representing the four representative PPO genes aforementioned. The transgene PGAS cannot be translated into a functional protein, but its expression can suppress the PPO genes, resulting in non-browning.
The second is a selectable marker gene called nptII of resistance to kanamycin, which is needed to select transgenic plants carrying the transgene. Gene nptII exists in many soil-borne bacteria and is used widely in other GMO crops. More importantly, the NPTII protein, product of nptII, is not detectable in mature Arctic Apple fruit.
Important Points To Remember
An important fact about Arctic Apples is their potential cross-pollination with conventional apples. If that occurs, the transgene will be present only in seeds and the eatable tissues remain non-GMO. In general, apple seeds cannot easily become trees in an orchard.
Lastly, Arctic Apples are similar to their non-GMO counterparts in quality, yield and resistance to diseases and insect pests.
In short, non-browning Arctic Apples contain two extra genes compared with their non-GMO parents, i.e. PGAS and nptII. The former is derived from apple DNA and does not produce a protein, whereas the latter is from bacteria and produces non-detectable protein in mature fruit, and is unlikely to pose a health threat to consumers.
Questions And Feedback Welcomed
If you have any questions or comments, I welcome your feedback. Please contact me by email or by phone at 315-787-2496. I can also be reached by mail at the following address: Kenong Xu, PhD; Asst. Prof. of Tree Fruit Genomics; Horticulture Section, School of Integrative Plant Science; Cornell University, NYS Agricultural Experiment Station; 630 W. North Street, Geneva, NY 14456.