They once stretched from Maine to Mississippi and were as tall as the famed redwoods. Today, American chestnut trees are a rare sight. In fact, scientists keep the locations of adult chestnut trees closely-guarded secrets.

These natural wonders helped to build the United States. Lumber harvested from American chestnut trees is naturally resistant to rot. If they were still standing tall today, then the median home price could be up to $4,000 lower by simply avoiding the purchase of chemically-treated wood. American chestnut trees provided habitats for dozens of unique species.

When the tree disappeared, so, too, did several others animals, most notably the passenger pigeon. The redwood rival also provided local economies unique foods, materials, and even beers.

How did this titan fall?

Deepening trade ties between East and West in the early 20th century led to the accidental import of many invasive species, including the fungus Cryphonectria parasitica. The microbe causes blight in several tree species by excreting oxalic acid, which causes molecular mayhem inside plant cells. The primary driver is a pH imbalance. As plant cells rush to mop up negatively-charged chemical compounds, normal cellular processes are disrupted. Reduced autophagy makes cells less efficient at recycling aging or dysfunctional proteins, while increased reactive oxygen species (ROS) and cell wall degrading enzymes (CWDE) lead to cell death.

Although oak, maple, hickory, and other trees are also susceptible to C. parasitica blight, American chestnut trees have no natural defense mechanism. But scientists are closing in on a simple solution. By genetically engineering American chestnut trees with the OxO gene, scientists can essentially inoculate trees against blight. The OxO gene encodes for the oxalate oxidase enzyme, which neutralizes oxalic acid.

If approved for widespread environmental release by regulators, then genetically engineered American chestnut trees could provide a towering example of the power of genetic engineering -- and in our lifetimes. That's because this species is only functionally extinct. In other words, although few trees make it to adulthood, there are viable root systems underground across the eastern United States. Planting just enough engineered tree saplings may reawaken the dormant root systems, effectively de-extincting the American chestnut tree.