Enhanced Blight Resistance in Transgenic American Chestnut
In the time-lapse video to the right (top), you will see a small-stem blight resistance assay (1) demonstrating the high level of blight resistance in two of our new transgenic American chestnut trees (2). The time is compressed from 15 days to a little less than two minutes. Recording started the same day the trees were inoculated.
From left to right, the trees are a blight-susceptible wild-type American chestnut (C. dentata) called Ellis 1, a blight-resistant Chinese chestnut (C. mollissima) tree called 'Qing,' and two transgenic American chestnut lines called Darling 215 and 311. The Chinese and American trees are "controls" that show the difference between susceptible and resistant trees typically seen in the wild. The transgenic American chestnut lines are derived from the Ellis 1 line, so they are identical to the American control, except for the oxalate oxidase gene from wheat that we added to enhance blight resistance. Watch as the wild-type American chestnut dies from chestnut blight, while the Darling 215 and 311 trees survive just as well as the blight-resistant Chinese chestnut control. Make sure your sound is turned on for the full effect.
This video demonstrates that these Darling American chestnut trees apparently have similar levels of blight resistance to the Chinese chestnut tree. But upon further inspection, these trees might have even higher resistance.
Previous assay on even smaller stems:
The possibility that the transgenic American chestnut trees may have higher levels of blight resistance than the Chinese chestnut control is supported by another experiment using trees with smaller stems (figure below) and using a novel leaf inoculation assay developed in our lab. In the "very-small-stem-assay", both the Ellis American control and the Chinese chestnut died, while both the Darling American chestnut trees survived. The Chinese chestnut died in that assay because the stem was so small the fungus could overwhelm it more easily. But the oxalate oxidase gene in the Darling trees was apparently sufficient to block the fungus, even on these very small stems. Therefore, these American chestnut trees might have higher levels of resistance than the Qing Chinese control.
We will soon be taking these trees through the federal regulatory review process involving the USDA, the EPA, and the FDA. Once approved, these trees will be distributed to the public in a not-for-profit program to restore the American chestnut tree, thereby benefiting our forests. This is a lengthy and costly process and we need your support to make this happen. For a broader overview of the chestnut project at ESF, please view our TEDx talk (video on homepage).
Over the next five years, our goal is to grow ten thousand blight-resistant American chestnut trees to jumpstart the effort to restore the tree to its native range in North America. Take action right now to keep us going strong! By making a tax deductible contribution to our project, and by sharing this challenge with your friends and colleagues, you can join our team and help us meet the challenge of actually growing ten thousand blight-resistant trees.
1. Powell, W. A., P. Morley, M. King and C. A. Maynard. 2007. Small stem chestnut blight resistance assay. Journal of The American chestnut Foundation 21(2): 34-38
2. Zhang B, AD Oakes, AE Newhouse, KM Baier, CA Maynard and WA Powell. 2013. A threshold level of oxalate oxidase transgene expression reduces Cryphonectria parasitica - induced necrosis in a transgenic American chestnut (Castanea dentata) leaf bioassay. Transgenic Research 22, Issue 5 (2013), Page 973-982
American chestnut test for enhanced blight resistance
Time-lapse blight-resistance demonstration video