GE American Chestnut — Restoration of a Beloved Species or Trojan Horse for Tree Biotechnology?
About a century ago the American chestnut tree was attacked by the introduced fungal pathogen (Cryphonectria parasitica). This fungus drove the chestnut to functional extinction. Now, scientists at the State University of New York College of Environmental Science and Forestry (SUNY ESF) claim to have created, through biotechnology, a resistant American chestnut variety. They aim to petition the required regulatory agencies (USDA, FDA, EPA) for deregulation of their genetically engineered chestnut in the near future, with the stated goal of “restoring” the species to nature.
If it is deregulated, the GE chestnut would be the first GE forest tree species to be planted out in forests with the deliberate intention of spreading freely. Monitoring or reversing their spread, once released, would likely be impossible. Performing valid risk assessments of the potential impacts of GE American chestnut on forests, wildlife, water, soils, pollinators or people, is hampered by our lack of knowledge about both the ecology of the American chestnut and forest ecosystems. Furthermore, since American chestnuts can live for more than 200 years, risk factors may change over the tree’s lifetime in unpredictable ways.
Critically, the choices we make about the GE American chestnut will set a precedent for the future use of biotechnology on other forest tree species and even more broadly, on the use of biotechnology, including new technologies such as gene editing, gene drives etc. as “tools for conservation.”
It is therefore critical that we carefully evaluate the case of the GE American chestnut. Towards that end, we recently published “Biotechnology for Forest Health? The Test Case of the Genetically Engineered American Chestnut.”
That paper was inspired by previous experience with a 2018 National Academy of Sciences study group on “The Potential of Biotechnology to Address Forest Health.” The case for using genetically engineered American chestnut for species restoration featured within the NAS study group. Similarly, it has also been featured in other contexts where the potential for using biotechnology in conservation has been evaluated. For example, it is presented as a “case study” in the International Union for Conservation of Nature 2019 report “Genetic Frontiers for Conservation: An assessment of synthetic biology and biodiversity conservation”. We therefore felt compelled to clearly articulate and share our reasons for opposing the GE American chestnut.
The American chestnut is a much beloved, iconic, “perfect tree” — that once was a dominant species along the eastern USA and into Canada. Prolific nuts reliably provided nutritious and delicious food, and fodder for livestock. The wood, rot resistant, easy to work with and pleasing to the eye was prized by the timber industry. Cryphonectria, “the blight” was a catastrophe — for the forests and wildlife, and for the human economies, especially those of rural Appalachia, where the seasonal nut harvest was key source of income, and sustenance. Restoring the American chestnut is a long-held dream for some people, even as our collective memory of chestnut-filled forests grows dim with the passage of time.
The American Chestnut Foundation has worked to implement a breeding program that would hybridize American chestnut with the naturally blight resistant Asian chestnut, and then backcross to produce a blight resistance tree that nonetheless preserved the growth characteristics of the American chestnut. Hundreds of thousands of hours of painstaking work across many years has gone into this breeding program — a long process that has slowly progressed, albeit with some setbacks along the way.
The SUNY ESF scientists claim that genetic engineering will provide a faster solution. After experimenting with various genes and combinations of genes, they have settled on using a gene sequence derived from wheat that causes the tree to produce an enzyme, oxalate oxidase, (aka OxO). This enzyme inhibits the spread of the fungus once established, making it less lethal to the tree. OxO is not uncommon in nature, and has been experimented with in a variety of common crops. In their promotional materials, the scientists are careful to highlight that OxO is common, and that the gene comes from ordinary wheat — conjuring images of saving the chestnut with nothing more dangerous than a tasty slice of buttered toast.
But will the OxO trait really enable restoration of the species? This is highly unlikely. First of all, engineering resistance to fungal pathogens in general has proven extremely challenging. Biotechnologists have long struggled to do so with familiar common crops with which, unlike forest tree species, we have plenty of prior experience. In spite of many, many efforts, only a single fungal pathogen resistant crop is commercially available (the Simplot potato, resistant to late blight). The problem is that fungi are very good at finding new ways to evade plant defenses. There is a virtual arms race going on between plants, evolving new defenses, and fungal pathogens, evolving new ways around those defenses. Hence making durable effective resistance is extremely difficult. As well, when plants invest in defending against a pathogen, their growth is often stunted or otherwise compromised and they can become more susceptible to other pathogens or stresses they encounter.
SUNY ESF’s OxO engineered chestnut trees appear to be resistant to the blight — but only young trees in controlled lab and field trial conditions have been tested. The oldest trees tested to date are only about 15 years old — other more recently developed lines are even younger. Yet chestnuts can live for over two hundred years during which time they may experience many diverse conditions — weather extremes, insects and pathogens etc. that could affect the expression of the OxO trait, or other characteristics of the trees. We cannot reasonably assume long term durable blight resistance in natural forests based on extrapolation from results on very young trees under controlled and laboratory conditions.
Go to Earth Island Journal to read the entire article.