TACF is no longer supporting development of D58 American chestnut trees
tacf.org
tacf.org
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.
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.
The pest is the emerald ash borer. Emerald refers to the color of the beetle. It's emerald ash_borer, not emerald_ash borer.
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.
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.
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?
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.”
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.
Wet lab is hard, and everyone is chasing the eureka moment.
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.
I wish them luck.
"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. "
emphasis my own
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.
Ballpark how many is not that many?
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?)
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 have quite a few acres and local contacts in my area that also grow trees. Feel free to reach out.
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.
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.
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.
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.
Are they doing okay?
It looks like they have a good plan for future engineering: Induced expression only in cells in the infected part of the tree.