News flash: genetic engineering may save the American chestnut tree

October 27, 2015 • 8:15 am

The American ChestnutCastanea dentata, was once a proud denizen of eastern U.S. deciduous forests, and prized for its wood. Then, in the early 1900s, the fungus “chestnut blight,” Cryphonectria parasitica, was introduced to the U.S. from Japanese nursery stock. Within a few decades, it wiped out around 4 billion chestnut trees.  Since the fungus is airborne, a few adult trees have survived in the East if they’re several kilometers from the nearest tree, and some trees survive outside the natural range; but the species isn’t coming back. When a tree dies or is cut down within the natural ranges, saplings will sprout from the roots, but before the tree can reproduce it’s invariably killed by the fungus.

Restoring the tree has been a tough problem, as the fungus persists. The American Chestnut Foundation (ACF), a pretty big organization, has done its best by spreading seeds from fungus resistant trees and so on, but now there’s additional hope—thanks to genetic engineering. (Reader Hempenstein is responsible for sending me this brand-new information.) The chestnut is in fact now a Genetically Modified Organism (GMO), with a gene injected into the DNA that makes the tree resistant to blight.

First, check out the photo below, which has just been made public. Left: American chestnuts showing effect of blight. Center: GMO (transgenically engineered) chestnuts infected with blight. Right: Chinese chestnut (Castanea mollissima), showing its susceptibility to blight.

The following caption and information were provided in an email by Bill Powell, a professor of Environmental Science and Forestry at the State University of New York at Syracuse, Director of the Council on Biotechnology in Forestry, and Co-Director of the American Chestnut Research & Restoration Project. His work is supported by the ACF.
The take-home message:  a single enzyme OxO, whose gene is engineered into the American chestnut genome, confers blight resistance.

This is a small stem blight resistance assay of Ellis 1 wild type American chestnut (left), Darling 54 transgenic American chestnut (center), and Qing Chinese chestnut (right). The Ellis 1 and Darling 54 lines are clonal except that the Darling 54 has the oxalate detoxifying enzyme gene protecting it.  All were infected with a highly virulent strain of the blight fungus, EP155.  After one month, all the Ellis1 were wilted, all the Darling 54 survived (and are still surviving today), and five of the six Qing eventually wilted.  This is demonstrates the high level of blight resistance in the Darling 54 line.

Interestingly, we can still isolate the blight fungus from the Darling 54, showing that the OxO doesn’t hurt the fungus. It just neutralizes its weapon, oxalate.  This is important because by not killing the fungus it greatly reduces the selective pressure to select fungal mutations that may overcome the resistance.  Therefore it should be a very sustainable resistance.

This resistance is heritable as a dominant trait and therefore when outcrossing with surviving wild type trees, half the offspring will be fully resistant.  We also have a easy leaf disk assay that can identify which offspring carry the resistance gene.  This will allow rescuing the genetic diversity of American chestnut that still survives in the forests.

You can see much more information (and a video of the blight-resistance assay) here. If the FDA, EPA, and USDA approves this (and I’m hopeful), the resistant seeds will be distributed for planting, and perhaps these giants will grace our forests again. I wonder if there will be a public outcry against the use of GMO chestnuts.

The fact that the resistance is dominant is a good thing, for any tree with the gene will survive, and those lacking it will not. That means that there’s no barrier to the spread of the resistant trees, even if the added gene gives them reduced fitness compared to the susceptible trees in the absence of the blight.

Here’s Powell talking about the significance of this tree,and describing the restoration project in a nice 15-minute TEDx lecture:

61 thoughts on “News flash: genetic engineering may save the American chestnut tree

      1. A glorious link, thank you. A good read is A Walk in the Woods, which puts the chestnut blight in perspective. (a Redford movie that just came out gets “meh” reviews; I cannot vouch for it. Book is great, though.)

        The loss to our forest habitat has been incalculable. The approach, detailed in your above link, is an example of science at its finest.

        1. I love Bill Bryson’s writing, and agree that A Walk in the Woods is excellent. I haven’t seen the movie, but imagine how it must feel to be told that “We’ve got Robert Redford to play you”!

  1. What a magnificent conservation acheivement. It is especially interesting that the resistant strain doesn’t kill the fungus, lessening the selection pressure for resistance and making the resistance more sustainable. I do wonder about differential reproductive success of the fungus in resistant vs non-resistant trees, though.

    1. My understanding is that it’s maintained in certain oaks (also in the Fagaceae) like post oaks. The fungus doesn’t seem to have evolved greater virulence to kill post oaks, and actually there’s an argument (source forgotten but perhaps PCCE will remember who I’m thinking of – it was in a small book IIRC) that pathogens evolve toward non-lethality as a mechanism of enhancing their survival. That’s more in re. viruses, tho, I think and not sure that might apply to fungi, tho.

      1. That pathogens tend to evolve –> less resistance is something that I have heard about from time to time.
        The idea is that there is selection against quickly killing a host since that means less time to spread to other hosts.

      2. That is correct. It’s more obvious in viruses due to smaller genome sizes, shorter generation times, and, in the case of RNA viruses anyway, significantly higher mutation rates; however, the model should hold true among other pathogenic species.

  2. Very proud that my son decided to study at SUNY-ESF, not only for this reason. Got to hear an interesting talk by his dendrology professor on the American Chestnut work when we were up for parents’ weekend last month.

    1. Do these trees produce the edible chestnuts. I love them roasted. I think the good ones come from California and Northern Italy. What? GMO’s rule!! Where would we be without GMO’s?

      1. Yes, the nuts are edible (in contrast to unrelated horse chestnuts). One of the things that’s barely remembered (since ethnobotanists and those sorts hadn’t yet arrived on the scene to document the catastrophe) is the impact the tree had on rural populations, many of whom lived largely on a barter economy. They turned their livestock out into chestnut groves to fatten in the fall, and they also turned their children out into the forest to gather the nuts that they then took to the local store to exchange for goods. The nuts made their way to New England, where they were sold roasted by street vendors.

        By one estimate at the time, tho, a rocky hillside of chestnut trees produced the same food value as an acre of wheat in the midwest.

          1. Oops, yeah, Buckeye. One of the major producers of edible Chinese and Am hybrid chestnuts is Empire Chestnut in Carrollton. A nice guy runs it. He sells out early.

        1. Plus, they told us, before the blight the American Chestnut alone was like 30% of the hardwood supply in the Northeast US. We’re doing renovations, and our contractor was salivating at the idea of a steady supply of Chestnut for finish work.

          1. For the meetings @ Penn State I decided to look for a B&B to stay in. I couldn’t have gotten luckier when I picked the Reynolds Mansion just north of State College in Bellefonte. The place was built in 1885 and what wasn’t clear from the pix on their website was how original especially the first floor is. The kitchen and dining room are trimmed in chestnut, and they were delighted to learn more about the whole effort.
            And if some pre-blight (not wormy) salvage chestnut near Pittsburgh might be of interest – I have 14 12′ 2×8’s – let me know. TACF might also be able to put you in touch with a disassembled chestnut barn that’s looking for a home.

    1. I imagine it will be the same as the objections to GMO corn and soybeans. I.e. not particularly rational.

      1. There’ll be predictable knee-jerk objections, but without Monsanto in the picture and all the arguments laid out by the folks at SUNY such objections will be harder to justify.

        Plus, objecting to this effort is also an objection to feeding charismatic woodland fauna.

    1. A memory of my childhood. Driving down suburban streets that were a dark tunnel of huge and shady elm trees. They were wonderful.

    2. My hope, too. I recall reading once about a single resistant elm which was being reproduced, but tree nurseries in my area say they haven’t heard of it — and sell no elms.

  3. a single enzyme OxO, whose gene is engineered into the American chestnut genome, confers blight resistance.

    I red-flagged on this, thinking “That’s a red flag for a resistance that it’s easy for the targetted organism to evolve around.
    Fortunately, the researchers obviously saw that flag waving :

    Interestingly, we can still isolate the blight fungus from the Darling 54, showing that the OxO doesn’t hurt the fungus. It just neutralizes its weapon, oxalate. This is important because by not killing the fungus it greatly reduces the selective pressure to select fungal mutations that may overcome the resistance.

    This concept of winning but not killing the enemy … surely the NRA would object that the correct solution is to pay them to develop rapid0fire machine guns capable of locking onto and shooting every one of those evil spores!
    Sorry, I need to clean the spittle off my keyboard.
    Watching the TED talk : that’s a chunky tree. Good to see a resistance developed like this.
    Britain lost most of it’s elms in the 1970s similarly. (I learned to handle an axe in the efforts to fell around infestations. We failed, but we did manage to manage the loss to keep the forest in question in good ecological status.) We’re facing a potentially similar situation with ash. It’s a general problem of moving biological goods around the world.
    I’m sure this won’t disturb the people who scream about “Frankenfoods” – their objections are mostly not based on evidence.

  4. Nice result of course, but as a non-native English speaker I find it mildly humorously that I should now care for old chestnuts.

    1. I didn’t encounter much in the way of chestnut products when I was in Sweden, but the European chestnut, Castanea sativa, is also susceptible to the fungus, altho it seems to have some resistance on its own, and is also helped by a double-stranded-DNA hypovirus that infects the fungus (it also serves as the model for dsDNA hypoviruses), but that hasn’t been of as much help with the American trees for a variety of reasons.

      Anyway, particularly in Spain, Italy and Turkey, chestnuts represent an important economic crop. (At the meetings at Penn State that I just returned from, a post-doc from Spain, now working in a lab in Finland, was also in attendance). And every fifth year the Int’l Soc Horticultural Science devotes its annual meeting to Chestnut. In 2011 it was in West Virginia. Next year it’ll be in Turkey.

      1. I may be just in that range. A colleague I sent this article to tells me that there is a centre for American Chestnut restoration work in nearby where I live. So bonus!

  5. I grew up on a 30-acre piece of mostly-wooded old farmland near Atlanta. When I was a child my father pointed out to me the old stumps and logs of dead chestnut trees in the woods, which were still intact despite having died decades earlier – the outermost part of the trunk seems to have some great resistance to rotting, and typically looked kind of like bluish-gray driftwood.

    Many of these stumps were still visible when we finally sold the land a couple of years ago – the trees had probably died in the 1920s or 1930s.

    1. Yep, I learned of the plight of the chestnut when I was something like 5y/o, up on Skyline Drive where my parents would go camping. Many of the chestnut ghosts were still towering over the canopy back then (~1955). In the ’30s and ’40s there were whole ghost forests, and the souvenir stands had postcards showing them.

      Jimmy Carter, who is honorary (and enthusiastic) president of the Am Chestnut Fdn – see comment to follow – learned of the plight in a similar way as a farm kid in Georgia where the blight was just making its way thru in the mid-30’s. They had a few chestnuts on their farm, and when he learned that he could trade one chestnut for three marbles (supply and demand – an early economics lesson, too), that was something that caught his attention.

      1. It occurs to me…a dead tree represents an awful lot of biological material in the environment that’s not available to other forms of life until after it’s decayed. That it takes so long for these trees to decay…is going to say something about the ecosystem, and the very least. Has anybody paid much attention to that angle? I’m sure, but….


        1. I don’t think that’s been explored except that tree borers moved into the wood after the mass near-extinction (the fungus doesn’t kill the roots and they continue to send up shoots that then get knocked back once the trees reach nut-bearing age or shortly thereafter, so there continues to be a source of germplasm). That’s the origin of “wormy chestnut”, from the massive amounts of salvage chestnut timber that arose after the blight came thru – a lot of that was used as the core wood in veneered furniture.

          But some attention is being given to the effects of the additional gene on insects like leaf miners and that sort of thing.

          1. I think they’re probably reproducing in places still — they aren’t all killed as saplings. About a year ago I found several large Am Chestnuts (12″ d.b.h., c. 50 ft. tall) in mixed forest (mostly oak-maple) near Narragansett, RI. These were not the monsters that apparently were once common, but definitely mature. Well past initial nut-bearing. I see the root-sprout saplings fairly often in the woods when we’re back there, but these were the largest I’ve encountered. Perhaps natural resistance locally?

          2. I think they’re probably reproducing in places still — they aren’t all killed as saplings. About a year ago I found several large Am Chestnuts (12″ d.b.h., c. 50 ft. tall) in mixed forest (mostly oak-maple) near Narragansett, RI. These were not the monsters that apparently were once common, but definitely mature. These were well past first nut-bearing. I wonder if natural resistance evolved — or if it’s just a lucky stand with no fungus about.

          3. There are rare survivor trees all across the original range – some particularly large ones up in Maine – but the experience with all of them has been that trees produced from their nuts show at best only marginally increased resistance to the blight.

            But, if you’d like to make the Chestnut Fdn aware of the trees you found, contact PCCE I can put you in contact with someone in the organization in RI.

    1. That the work has been going on has been out there, but the level of control in the experiments shown in the pic is much greater than last year (as in Dr. Powell’s TED talk), and are at a level that discussions can start with federal regulatory agencies. As I understand it, a preliminary meeting has already been held, and the reception was more favorable than even the SUNY group expected.

  6. It may particularly interest PCCE that the Am Chestnut Fdn was founded (along grad school dropout Phil Rutter) by an Emeritus Professor, Charles Burnham, a corn breeder from U Minn whose ancestry was pretty impressive to begin with – in the late ’20s he was at Cornell, along with fellow grad students and future Nobel Laureates George Beadle and Barbara McClintock, as seen in the famous pic. Their mentor, Rollins Emerson, had some role in rediscovering Mendel’s work, altho exactly what that was has never been clear to me.

    Burnham was also noteworthy before his retirement as the mentor of Norman Borlaug (Nobel Peace Prize, 1970). Borlaug was a personal friend of Jimmy Carter, who enlisted his enthusiastic (and continued) support as honorary president of the organization.

    Other people whose interest and support of the mission that might surprise you:

    Dolly Parton, who provides support for graduate work on chestnuts at U Tenn thru her Dollywood theme park. As I understand it, this is the only scientific endeavor her foundation supports – the rest goes toward early learning/childhood literacy efforts.

    Chuck Leavell, keyboardist for the Rolling Stones, whose other life is that of a Georgia tree farmer. This dual life may in part stem from an early age when he suddenly decided he wanted to be a musician when he grew up, and ran to inform his mother of the news. She laughed, “Oh, honey, you can’t do both!”

  7. Very good to hear about this. I remember my dad using chestnut to makes some cabinets and they were really nice. Very good wood to work with but was in very short supply for this very reason.

    I don’t recall what killed the Dutch Elm but that was a great loss as well. They started dying in the Midwest when I was a kid and pretty soon they were all gone.

    If you want to see some of the toughest import customs of all plants or ag products, check out Japan. They are very strict on everything for this very reason.

  8. If there were a god who’s responsible for everything, genetic engineering would be taking over the reins on grounds of incompetency. And it’s a good thing. What kind of a God loves tree fungus more than trees?

    But in the final analysis, seems to me it’s still an arms race. The bad guys (tree fungus, etc.) are still adapting; we can’t ever let our guard down. “Keep watching the skies!” [last line from ‘The Thing from Another World’]

    1. Yep, everything loves chestnuts – the blight fungus, the root rot ink fungus, Phytophthora cinnamomi (against which resistance is apparently carried naturally at a single locus, so it’s a tractable problem; chestnut gall wasp, Dryocosmus kuriphilus (vs. which at least there’s another parasitoid wasp that likes to eat it; and an ambrosia beetle borer.

      Then there’s the damn hemlock wooly adelgid, the emerald ash borer, oak wilt sudden death fungus, and of course the Dutch elm fungus. Seemingly the great majority of the charismatic megaflora. But does anything want to attack Ailanthus trees? Hell no!

        1. Oops, the above comment was supposed to have been to #20 and I’ve just re-copied that down there. I’ll get PCCE to remove this one in the morning.

          This is really GREAT news about the wilt. Thanx!!!

  9. The achievements of science in the area of transgenic engineering is awe-inspiring. It’s amazing to think how far it might take us. (A joke here about dinosaurs might be appropriate.)

  10. There were Chestnut trees in Toronto when I was a boy. We kids used the nuts in a game. You’d drill a hole in the nut, push a string through and use it like a medieval weapon to crack the other guys nut. Probably those trees are gone now. Nice to hear they are coming back so my great grandson can enjoy the combat.

  11. This is so much better than what American Chestnut foundation *has* been doing, which is crossing our native species with Chinese chestnut. That program has been running for so long that there’s probably no stopping it, and huge numbers of hybrid trees (only ~94% native genetics) have already been planted into natural areas. They were apparently selected for characteristics the breeders wanted to see in a timber tree, not just for disease resistance, which is what bothers me about the whole project.

    1. Um, no, first, in reverse order, selection has distinctly NOT been solely on American (timber tree) characteristics. That is part of it, but in the breeding orchards trees are inoculated with two strains of the fungus. First, a relatively mild strain and then aftern an interval a vigorous strain. Most of the third-generation of the third generation backcross (BC3F3) trees don’t survive that, but some do to varying degrees. Culls are made of those down to the ones with best resistance, and those are the parents for the next generation. I saw one such particularly nice specimen, over 20′ tall, at Penn State last weekend. All this takes time of course, since unlike annual crops it takes years for the trees to reach sexual maturity. A few yrs ago the program reached a point that at its outset had been expected (when it was started on paper in 1983) to take till 2040. It was largely thru the efforts of one tireless and selfless plant pathologist at the farm in SW VA, Fred Hebard, that the generation time was cut to something like four years.

      In a perfect world, things would have worked out better, but this is science and you take the results you get. To even think of mounting an effort like this in the 80’s, after the USDA & Forest Service had written the tree off, took monumental brass balls, and also a vision to the future that they knew they wouldn’t live to see. Borlaug had been with the Forest Service in the ’40s, and after Burnham (who eschewed the trappings of retirement like golf in lieu of spending time in the library, finally getting a chance to read up on things he hadn’t had time for while active faculty, and in so-doing finding that all efforts had been put into crossing the F1’s with Chinese) called him and asked “What the hell were you guys thinking?” Borlaug’s reply was something like, “We didn’t know anything about genetics back then.”

      Further, applying transgenic technology to trees wasn’t available back in the ’90s. I’m not sure when the SUNY effort started, but it was after the backcross program started, and it’s only been recently that any trees have come of it. And altho things seem favorable for Federal approval, that can’t be counted on.

      Finally, TACF has the infrastructure in place to propagate trees, and get them into seed orchards, and so forth. It has by no means been rendered obsolete by these results. If the transgenic trees are rolled out into the wild, the gene will spread thru any populations out there like wildfire. And it’s also well to remember that a successful heterozygote does not necessarily beget a successful homozygote (viz. sickle-cell in malarial environments), so some hedging is still reasonable on those grounds alone.

  12. If public golf courses were replanted with resistant chestnut seedlings, it could be the beginning to solving 3 (or 4) problems at once.
    1. enhancement of American Chestnut survival and genetic diversification;
    2. carbon dioxide abatement;
    3. expansion of public-access park woodlands in urban areas;
    4. reduction of government subsidies to elitist sports, prejudicial to objectives 1 to 3.

  13. We had a healthy chestnut tree in MD. It produced a large crop all 18 years we lived in that house. Dad used to take nuts to the local parks and plant them, hoping the squirrels and chipmunks wouldn’t find them. I hope there are some healthy chestnut trees in those parks.

  14. More information on American Chestnut Restoration is available on the American Chestnut Cooperators Foundation website , a non profit organization that uses pure American Chestnuts in a more traditional breeding program to enhance native resistance and develop durable blight resistance. Although often downplayed, the research and progress of this program are outstanding. mirror site

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