In 1990, the New York chapter of The American Chestnut Foundation (TACF) and the State University of New York’s College of Environmental Science & Forestry (ESF) began a collaboration to take a complementary approach to the backcross breeding program to develop blight resistant American chestnut trees. This was an intentional decision to use every tool in our toolbox to address the serious problem of chestnut blight. One of those tools, developed at ESF, involves adding new genes to the American chestnut, which allows the tree to withstand blight with almost no damage. Genes being tested come from the Chinese chestnut and other plants.
The most effective gene tested to date encodes a detoxifying enzyme called Oxalate Oxidase, or OxO. OxO breaks down oxalic acid, which is one of the primary “weapons” the blight fungus uses to attack chestnut trees. The naturally blight-resistant Chinese chestnut tree makes use of a similar mechanism as a part of its resistance strategy, but it is not as effective as the OxO gene currently being tested in American chestnut. This OxO gene provides dominant blight resistance, meaning that if these trees are crossed with surviving American chestnut trees, half the offspring will inherit the OxO gene and therefore be fully blight resistant. This characteristic allows the possibility of rescuing much of the remnant genetic diversity and local adaptations in the surviving population, a key element in the conservation of the American chestnut.
The OxO gene being used comes from wheat, but it is a common defense gene in many food crops and other plants. Wheat is grown in many areas within the American chestnut range and the rest of the world, and wheat products are found in a huge variety of food and animal feed. This gene was specifically chosen for use in chestnuts not only because of its effectiveness, but also because it shouldn’t pose any new health or environmental threats. (The OxO gene is not related to gluten or other known allergens). Experiments are ongoing to confirm the safety and effectiveness of this gene in the American chestnut’s natural environment, but so far, all results indicate that American chestnuts with the OxO gene are as safe as American chestnuts or trees produced through hybrid breeding. This is not surprising, since adding a new gene through this process makes such a small change to the American chestnut tree: OxO-containing American chestnuts still have 100% of their native American chestnut genes, and the addition of 2 genes (the OxO and a selectable marker gene) during the transformation process results in a tree that is still >99.999% pure American chestnut. For more information about the OxO gene, see http://www.esf.edu/chestnut/genes.htm.
The USDA, EPA, and FDA tightly regulate American chestnuts transformed via the process of adding new genes. All three agencies must rigorously evaluate the trees, along with potential health and environmental effects, before the trees can be distributed or widely planted. SUNY-ESF and TACF are firmly committed to the safety of people and wildlife that interact with chestnuts, and with the integrity of their surrounding environment, so no trees will be released if there is any indication of increased risks. But if American chestnut trees produced through this method are shown to be safe and durably blight resistant, and if approval is granted by all three federal agencies, SUNY-ESF and TACF would like to see them as an integral part of restoration efforts someday. These and future trees would significantly augment breeding efforts and help ensure the return of the American chestnut.