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Have you ever seen a growth on tree that looks like a butt? These butts are a result of natural genetic engineering! This discovery led an NC scientist and avid hiker to create the first genetically modified plants.

West Asheville Park

Crown Gall Tumor

Another name for this junk in the trunk is a Crown Gall Tumor. These growths are the result of a bacterial infection caused  by Agrobacterium.  Living in the soil, the bacteria detects chemicals released by an injured tree. Once inside the tree the bacteria integrates a portion of its DNA into the tree genome. This is an example of naturally occurring genetic engineering! For a bigger tree the tumor will not harm the tree, but may inhibit the growth of smaller trees.

Mary-Dell Chilton

The Queen of Agrobacterium

In the 1970’s, Mary-Dell Chilton identified what was happening in the Crown Gall Tumor. She went on to create the first genetically modified plants by isolating the genes from the bacteria. These modifications can be used to create crops like golden rice which increase key vitamins to prevent disease and malnutrition. Mary-Dell spent much of her childhood (Southern Pines) and later professional life (RTP) in North Carolina. She is an avid outdoorswoman and hiker, she is known as the “Queen of Agrobacterium”.

Below is an excerpt from, “My Secret Life” , an essay by Mary-Dell’s on her personal and professional life. Click here to read more.

What is going on at the molecular level?

The DNA from the bacteria codes for many functions including acting as a tiny pair of molecular scissors and syringe. Once inside the tree, the bacteria cuts out its own DNA with the “scissors” and injects it into the nucleus of a tree cell with a “syringe”. At this point, the scissors are used to cut the tree DNA and insert the bacteria’s own T-DNA (transfer DNA) into the tree genome.  Scientist like Mary-Dell have been able to isolate the bacteria’s DNA and replace the T-DNA with whatever gene they want to put in a plant. But telling the gene exactly where to go, ie where to insert itself in the genome is tricky and very important. If the gene is inserted in the wrong place it could cause disruption in other important genes and biological processes. This is where tools like CRISPR can be used to help guide the insertion of the gene, but that is a story for another day.

credit: Guo, et al. 2019

Further Reading

M.D. Chilton, “My Secret Life,” Annu. Rev. Plant Biol., vol. 69, no. 1, pp. 1–20, Apr. 2018, doi: 10.1146/annurev-arplant-032717-090606.
M. Guo, J. Ye, D. Gao, N. Xu, and J. Yang, “Agrobacterium-mediated horizontal gene transfer: Mechanism, biotechnological application, potential risk and forestalling strategy,” Biotechnology Advances, vol. 37, no. 1, pp. 259–270, Jan. 2019, doi: 10.1016/j.biotechadv.2018.12.008.
E. W. Nester, “Agrobacterium: nature’s genetic engineer,” Frontiers in Plant Science, vol. 5, 2015, [Online]. Available:
M.E. Gearing, “Good as Gold: Can Golden Rice and Other Biofortified Crops Prevent Malnutrition?” Harvard University Blog. Available:

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