The headline here does not come from the original article and is misleading. The actual article title is "Darling D58".
The closest subheading matching the title given here is "Why TACF is No Longer Supporting Development of D58 or Deregulation of the Darling Line."
The American Chestnut Foundation is still most certainly pursuing its mission to reseed America with blight-resistant seeds. Just they've discovered that a previously promising line of seeds (Darling D58) is actually seriously flawed and efforts to work with that particular line will be abandoned.
I saw a video on this recently. It's super sad that such a magnificent tree (along with the American Elm) have been completely destroyed. So much majesty gone.
I became really interested in this topic after having my first roast chestnuts a couple years ago! Some of the interesting things I learned:
- Chestnut deforestation due to blight was a substantial portion of global deforestation in the early 20th century (IIRC half in 1920s and 1930s).
- Chestnuts were such a staple that they were considered poor people food in America. Some lamented that chestnut products (including chestnut flours) seemed to be all the general stores carried.
- The majority of all wood construction in early America was chestnut.
Wild that such a central part of American society vanished and I didn't even know beyond "chestnuts roasting on an open fire". Makes me wonder what other parts of our lives and culture will be lost with extinctions caused by climate change.
wild, but also reassuring that within a generation or two a change like this (and there will be many more coming with climate change) can be adapted to and forgotten.
Not familiar with that one, but sad to hear about.
It wasn't until I started growing apple trees that I realized how crazy hard it is to grow some trees. They're susceptible to insects, fungus, drought, flood, animals...etc.
Yep, had four dead ash cut down last year and a whopping 22 dead ash cut down a few weeks ago. The grub form of the ash borer can be found in the firewood rounds.
Fair! I was trying to be both succinct and communicate the setback to someone who might not follow the details. For those who might know TACF is working on seeds and makes them (with some hoops) attainable to the public, ceasing that distribution is the news.
That is disappointing, but I'm also a little curious - why did this go all the way to field trials if the gene insertion was completely screwed up, to the point of being on the wrong chromosome?
In November 2023, through molecular analyses performed by partners at the University of New England and University of Maine, TACF learned that the OxO gene of all Darling 58 trees was on a different chromosome than expected (chromosome 4 instead of chromosome 7). Upon further and additional independent investigation, scientists confirmed that the trees they had been researching were in fact descendants of a different event in the Darling line in which the OxO gene had been inserted into a coding region, causing a deletion in a known gene. That research has also indicated that the homozygous state (when an individual plant inherits the OxO gene from both parents, which occurs in 25% of offspring) is lethal, and that a majority of homozygous offspring die in the embryonic stage.
TACF researchers suspect that the performance issues of Darling trees stem primarily from the placement of the OxO gene as well as the constitutive expression of the OxO gene which is always “switched on” via the 35S promoter. Somewhat like having a constant fever, that constitutive promotion appears to result in high metabolic costs for the trees. All events in the Darling line use this promoter. Therefore, TACF is no longer pursuing research efforts with any event in the Darling line.
If you are breeding to insert a single, specific, gene, into a single, specific place, it would seem like you'd of course do some sequencing to verify that it went in at the expected place and didn't do anything else off-target (like cause deletions in an unrelated gene), before you invested a year in field trials.
Is sequencing of tree genomes still so expensive that it makes sense to fail in the field first and only then go looking for problems?
It's possible they checked before (and the article suggests they had an inclination where the gene should be) but the resultant backcrosses involved a spontaneous recombination of the relevant fragment. It's possible someone checked the wrong vial in lab, or mislabeled results. It's possible something funny "just happened".
Wet lab is hard, and everyone is chasing the eureka moment.
My reading of the article suggests they modified the genomes of multiple trees, and the “winners” that got into the field happened to have ancestors that had moved the target gene to a different chromosome.
They’re simultaneously trying to make precision modifications to the genome and also trying to preserve hundreds of wild strains.
If they succeed, the required technological advances will probably be broadly applicable.
"Upon further and additional independent investigation, scientists confirmed that the trees they had been researching were in fact *descendants of a different event in the Darling line* in which the OxO gene had been inserted into a coding region, causing a deletion in a known gene. "
Well for comparison the sunflower has around 30% more base pairs in it's genome than the human genome, kentucky bluegrass has more than double, spruces have around 7x as many, pines have over 10x, but oak has less than a third.
So it's kind of all over the place. Even relatively similar plant species within the same family can have massively different genome sizes.
Chinese chestnuts have a comparatively small genome but they were only sequenced in the last 4 years and to my knowledge they are the only chestnut to have been sequenced.
“Polyploid organisms have more than two sets of homologous chromosomes. For example, humans have two sets of homologous chromosomes, meaning that a typical human will have 2 copies each of 23 different chromosomes, for a total of 46. Wheat on the other hand, while having only 7 distinct chromosomes, is considered a hexaploid and has 6 copies of each chromosome, for a total of 42.”
This was often NOT done in many transgenic experiments 20 to 30 years ago. In mice transgenic insertions and inadvertent disruption of genes near the transgene insertion are only occasionally disruptive. The reelin gene disruption is a good example.
This work was started long before cheap whole genome sequencing.
However, comments are right—it was never too hard to examine the flanking sequence around the insertion site.
Just offered to help the team with telomere-to-telomere of the few rare wild American chestnut survivors. There are not that many.
You don't need to sequence the entire genome to know where copies of the gene of interest are located.
I'll edit that the research still looks worthwhile for the information they discovered. Using a highly expressing constitutive promoter showed that OxO is a good gene candidate for resistance, and now they can tailor it more with the wound-inducible promoter.
"American Chestnut Foundation is No Longer Supporting Development of D58 Transgenic Chestnut Tree Line" would be a better title.
This is a disappointing result as the D58 line appears to have problems described in the article. However, it seems that multiple parallel efforts are ongoing with other transgenic attempts as well as more traditional back-cross methods. The road to American Chestnut restoration appears to have encountered a significant setback but promising research is still ongoing.
Relatedly, I saw many American Chestnut trees on the Shawangunk Ridge over the summer. Several were blooming. Not sure whether they bore fruit (chestnuts). This is not uncommon. Of course, they eventually become blighted and die, but they can still attain a respectable size (20-30 feet?)
The current seeds given to the public the ACF were counting on have very poor survival/growth metrics and they're giving up on that line; big shame as those are the seeds they offered to donors (and thus a way of getting involved as as outsider).
I bought some of those seeds and I just thought I had a black thumb. I planted my surviving seedlings this fall, a month before frost, and I hope they will survive winter..
I live in blight region (NJ). We have American seedlings growing here for a few years now, but I don't have faith that inside the range they'll reach maturity.
Our mature American Chestnut tree is well established enough that it dies back some every few decades and recovers. This year I got 50 or so chestnuts out of it. I ate a few, they are great and never seem to get the weevil that the Chinese trees we have do (basically if I don't process the Chinese ones immediately after harvesting in a hot water bath, they will have a grub bore out of them in a week or so).
Been trying to find people outside blight region (somewhere like Michigan/Wisconsin) to plant the American ones so they have a shot. This tree is not a result of any of the ACF's crossbreeding, it's just a survivor that's over 100 years old.
I live in Nevada City, California. We have several productive chestnut trees growing around and I can't really tell if they're Chinese or American. They do not ever get anything growing in the nuts so maybe they're American. Otoh, the weevil might not be universal.
From the point of view of a book reader, that is a really bad book. Entire paragraphs simply restating the content of previous paragraphs with some minor additions of content.
The headline sounds like the final end of the experiments but to me it sounds more like a setback, e.g. eventually they hope to get a transgenic blight-resistant tree they can distribute.
It's a setback, but it's a pretty big one, since the whole lineage is now considered nonviable due to OxO replacing another important gene. So you have to go back and implement the gene somewhere else, or do what they talked about here, implement some kind of switch.
The is a chestnut orchard in the Santa Cruz Mountains (SF Bay Area) that has American chestnut trees in it (also European, and at least one Asian chestnut). It’s kind of neat because you can compare the chestnuts from the different species. American chestnut has the smallest nuts of the three, but they are the sweetest and most flavorful.
When i was little, we had a neighbor who had a few American Chestnut trees of bearing age. He had an annual business collecting and selling the nuts; he wouldn't let anybody know where the trees were.
still fondly recall the flavor of the real chestnuts.
I found a chestnut tree of moderate size on my property this year, and for time thought it might be an American Chestnut. Alas I eventually concluded that it was a Chineese Chesnut. Still a nice tree, but hardly as exciting.
Tried to respond to this before maybe the site will let me now. There's a redwood that was thought to be extinct that thrives in east coast conditions of the US. The dawn redwood is a fast grower, and while being the smallest of the redwood species is still quite a large tree. It was discovered in a valley in China I guess back in the 40's, previously only known to the fossil record.
We have one here planted in the 1970's that towers over my house and had one next to my childhood home. It's amazing they do as well as they do, but the concern now is genetic bottleneck since most of the seeds planted worldwide were from a few trees, so the successive generations I guess don't do as well as the ones in that valley do.
It is. Just finished dropping its leaves/needles for the winter. I've heard from a few arborists they've had people ask if their tree needed to be cut down thinking it was dead, only to be told that's just what it does in the fall (it drops later than most of the other trees). We couldn't ID the one by my old house when I was a kid (internet was still early, nothing like inaturalist). Thought it was a larch, which having seen the tree now makes sense. I have been wondering after the recent HN topic if it has similar fire resistance/recovery that the giant redwoods out west have, realize we don't really know how long it'll live in the here since all were brought in the past 80 years. When the landlord planted it he misjudged how big it would grow (seems to be a common theme with the ones I see growing around). Until we got cats these red squirrels would eat the seeds in the small cones it produces and chuck them at our roof.
Other than the squirrel issue I have that was resolved, the tree is a lovely tree and I have had many dreams of them and memories of sitting in the shade under them with my cat as a kid. It doesn't throw sap like a fir does and the branches are thinner and unlikely to cause major damage to a house if they do come down.
Click baity - they are ceasing distribution of blight resistant seeds that died more frequently than expected. It’s not viable in wild so no go.
This headline would have you thinking they’re holding back progress or something. But it’s clear they are the opposite, cutting their losses and investing elsewhere.
There is a pretty fascinating correlation here between growth rate and susceptibility to mortality from the fungal infection. Remove the toxicity of oxalic acid and suddenly growth rate reduces. Obviously there’s a ton of variables but, oversimplifying, it almost seems like a deal with the devil: increase growth rates but at the cost of increased mortality to the blight.
The 35S promoter is a really strong constitutive promoter. Just expressing the OxO gene from it could be enough of a metabolic cost as to be noticeably growth inhibitory, much less the effect of the unintentional gene knockout.
It looks like they have a good plan for future engineering: Induced expression only in cells in the infected part of the tree.
As someone who planted multiple trees on my farm and has been involved in this — definitely disappointing. None of my trees have made it to the phase blight typically gets them, and intend to keep them for the time being
The closest subheading matching the title given here is "Why TACF is No Longer Supporting Development of D58 or Deregulation of the Darling Line."
The American Chestnut Foundation is still most certainly pursuing its mission to reseed America with blight-resistant seeds. Just they've discovered that a previously promising line of seeds (Darling D58) is actually seriously flawed and efforts to work with that particular line will be abandoned.