TACF is no longer supporting development of D58 American chestnut trees

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?

Wow fascinating. Apparently it is a deciduous tree.

ACF/ESF is running the project. They are providing an update. No clickbait, and a very well written update at that.

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?)