Designing Chestnuts

In “Philosopher’s Corner: Genome Fidelity and the American Chestnut” (Issues, Summer 2017), Evelyn Brister presents a well-written and balanced account of the state of affairs regarding efforts to work around the blight plaguing these trees, and as someone who is in the middle of things, I have nothing to debate. But I would like to clarify and expand on some points.

Her claim that “Restoring the American chestnut through genetic engineering adds about a dozen foreign genes to the 38,000 or so in its genome” needs some clarification. It is true that we have tested dozens of genes singularly, and in combinations of two and three genes, but the first trees we will use in the American Chestnut Research and Restoration Project will have only two added genes. This is a small point, but the more important point is that the genetically modified American chestnut that we will use first will have all of its original genes. Therefore, it should be as fully adapted to its environment as the original, with only blight resistance added. Unlike in hybrid breeding, where you may introduce genes for unwanted traits, such as short stature or reduced cold hardiness, genetic engineering keeps all of the original genes intact and adds only a couple of genes.

In our work in the restoration project, we used an oxalate oxidase (OxO) gene taken from an enzyme in wheat to confer blight resistance in the American chestnut. This enzyme detoxifies the oxalic acid that the troublesome fungus uses to attack the tree. So it basically disarms the pathogen without harming it. But this OxO gene isn’t unique to wheat. Oxalate oxidase enzymes are found in all grains tested to date, as well as in many other plants, such as bananas and strawberries. In fact, the chestnut itself has a gene that is 79% similar to a peanut oxalate oxidase. So, the “genome integrity” that Brister discusses is not a simple concept, and defining it simply by the source of a few added genes is meaningless. It is better defined by how large of phenotypic, or functional, change is being made and how this affects the organism’s place in the environment. With the American chestnut, the change is very small and allows the tree to return to its natural niche in the forest.

Genetic engineering isn’t the answer to all pest and pathogen problems, but in some cases it is the best solution. It is only one tool, but it is a useful tool that shouldn’t be left sitting idle in the toolbox.

Professor and Director, Council on Biotechnology in Forestry

Director, American Chestnut Research and Restoration Project

Scientist-in-Residence, SUNY College of Environmental Science and Forestry

Should a genetically modified, blight-resistant American chestnut be reintroduced to eastern North American forests? Evelyn Brister contends that this question cannot be easily answered by an objective, all-knowing science, but is instead rooted in philosophical concerns about genetic purity and naturalness. Her discussion of genome fidelity and comparison of breeding and genetic modification offers valuable nuance to the public discourse on the American chestnut and genetically modified organisms (GMOs) more generally. But in her focus on philosophies of this tree’s genome, Brister seems to downplay concerns about harm to health and environment and social and economic impacts, noting that GM chestnuts are more likely to cause ecological good than harm, and that “the economic imperialism that has followed corporate control of GMO intellectual property” is a “nonissue” because researchers have pledged to make the GM tree publicly available.

In my own research on chestnut restoration, I have found that there are crucial political, economic, and ecological concerns that drive opposition and hesitation to GM chestnuts, and these concerns extend beyond issues of genome fidelity. Some observers worry, for example, that the blight resistance of a GM chestnut may not be sustained over the long term if the blight fungus adapts or if added genes are silenced, rendering chestnut restoration a costly and wasteful undertaking. Others hesitate to champion a project that has received financial and material support from the biotechnology industry, including ArborGen and Monsanto, fearing that the chestnut is being used as a ploy to sell the US public on the value and necessity of GM trees. Relatedly, there is concern that rapid regulatory approval of a GM chestnut will set a precedent for how commercial GM trees are viewed and regulated in the future.

Still other people are primarily concerned with inadvertent ecological effects: How will a genetically novel tree affect existing forest dynamics, food webs, and carbon cycling? How will it affect the spread of invasive pests, such as the gypsy moth, and health risks, such as Lyme disease? There is some initial evidence, for example, that gypsy moths may feed more heavily on a transgenic variety of chestnut, possibly leading to increases in gypsy moth populations, as Keith Post and Dylan Parry noted in an article in Environmental Entomology. Other research has suggested that chestnut restoration—whether through backcross breeding or GM techniques—may alter the geography of Lyme disease and potentially increase risk of transmission.

In short, opposition and hesitation to a GM chestnut are not merely rooted in philosophical concerns about genome fidelity, but are also centered on the broader political, economic, and ecological impacts that the tree may have in the world.

Brister notes in her conclusion that the debate about a GM chestnut “requires that we weigh metaphysical concerns about genetic purity with practical and ethical concerns about forest diversity,” which suggests that opposition is based primarily on metaphysical concerns whereas support is based on practical and ethical concerns. She deems it likely that “maintaining healthy forests will require not only the use of genetic technologies to modify tree species, but also to control the pests that are killing them,” and she further states that “we can’t afford to miss the value of our forests by getting lost in debates about the trees.”

This line of reasoning is tempting, but also silencing: it closes off debate and insinuates that questioning GM trees may be detrimental to the state of forests more broadly. I would encourage everyone to ask: Where does this idea—that genetic modification of tree species and pests is necessary to maintain forest health—come from, and what evidence is there for it? Perhaps more important, what other options and strategies are overlooked, foreclosed on, or disinvested in when we decide that healthy forests require molecular interventions?

Assistant Professor of Geography

University of Washington

Evelyn Brister describes two research programs that aim to restore the American chestnut to US forests by making it blight-resistant. One program has created a hybridized American chestnut by using traditional genetic backcrossing; the other has created a blight-resistant genetically modified (GM) American chestnut. In her article, Brister explores the likely objections to the GM option.

Brister focuses on loss of “natural integrity” as the main concern raised by the GM chestnut. But as she indicates, the idea of natural integrity is problematic. It is not obvious that a hybridized chestnut has more natural integrity than a GM chestnut. And why should natural integrity matter anyway, especially when forest diversity is at issue?

Brister is right to raise these questions, but there’s more at stake than she suggests. She identifies natural integrity with “genetic integrity” or “purity,” interpreted as something like “closeness to the original genome of the American chestnut.” Certainly, some people will be concerned, in both cases, that the genetic composition of the new chestnut trees lacks purity in the sense of genetic closeness to the ancestor chestnut. But worries about naturalness frequently also concern how something came about, not just what it is composed from.

The degree of worry about both types of chestnuts might be related to the degree of intentional human interference involved in producing them. In the case of the GM chestnut, this is especially likely to lie behind concerns about insertion of a wheat gene to enable resistance to blight. It’s not just that the wheat gene is less natural in the sense that it is normally located in a more genetically distant plant. It’s also that the wheat gene could not have gotten there without human agency. Likewise, hybridizing an American chestnut with a domesticated Chinese chestnut draws on the long heritage of human agency required for the creation of domesticated trees.

Opening up questions about human agency, though, introduces other broader concerns about “wildness.” Suppose either of these chestnut varieties is planted in “the wild.” Would the forests into which these trees are introduced remain “wild” after we have deliberately released them? And would they require further human interventions once they have been planted, essentially creating a managed woodland?

Unlike Brister, we think that the potential ethical conflict here is not just about genetic purity, but that much broader wildness values are at stake. These trees will have a genetic set determined by people, and they will be planted and managed at a time and place, and for a purpose, determined by people.

Of course, perhaps there is no realistic alternative to a human-originating forest. Or even if there were such an alternative, it may be that the value of forest diversity should indeed outweigh not only genetic purity but also other wildness values. But nonetheless, we should not underestimate the importance of protecting the remaining wildness in US forests.

Professor of Philosophy

Texas A&M University

Professor of Bioethics

University of Copenhagen

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Cite this Article

Sandøe, Peter, Clare Palmer, Christine Biermann, and William A. Powell. “Designing Chestnuts.” Issues in Science and Technology 34, no. 1 (Fall 2017).

Vol. XXXIV, No. 1, Fall 2017