|MadSci Network: Genetics|
The "glowing plants" you read about were the culmination of years of research into techniques for inserting foreign genes into plants. Inserting DNA into bacteria had been accomplished long ago, and newer techniques were being developed to insert DNA into animal cells, but their impervious cell walls made plant cells very difficult to "transfect". Even more problematic, once a plant cell was transfected, how could a complete adult plant be made from the cell to produce a transgenic plant (transgenic mice - mice carrying foreign genes - had already been produced). Early work in genetically engineering plants required complex machinery and expensive procedures with unsatisfying results, as many times the novel DNA was merely destroyed or ejected by the plant cell. Finally researchers found a helpful tool in Agrobacterium tumefaciens, a soil bacterium that infects many plants, and while infecting the cells stably inserts a small piece of "T-DNA" which is then used by the plant cell, even after the bacteria are removed. The bacteria also caused the plant cells to grow and divide in culture, forming clumps of undifferentiated tissue, that under special conditions would grow into an entire plant.
To test their abilities to make transgenic plants using these new techniques, scientists needed a "tag" - a protein that would be easy to test for but would not harm the plant - to follow the DNA from the bacteria into the whole plant. Two laboratories decided to use bioluminescent tags, since the product, light, did not require special equipment to detect. In 1989, Csaba Koncz, of the Max Planck Institute in Cologne, Germany, used A. tumefaciens to introduce the bioluminescence gene from the luminescent bacterium, Vibrio harveyi, into cells of the tobacco plant Nicotiana tabacum. This experiment was only partially successful, because the bacterial gene was actually two genes, LuxA and LuxB, both of which had to be properly expressed to get the light reaction. So in 1990, Wayne Barnes, here at Washington University in St. Louis, Missouri, used A. tumefaciens to introduce the luciferase gene (Luc) from the firefly, Photinus pyralis, into tobacco plant cells, with great success, getting adult tobacco plants that glowed green after the application of luciferin. Since then luciferase has become a staple of genetic research, and the techniques developed by Koncz and Barnes have been extensively used to continue research on plant genetics, and by several companies to produce crops that are resistant to predation and spoilage.
Koncz, C., Martini, N., Mayerhofer, R., Koncz-Kalman, Z., Korber, H., Redei, G. P. and Schell, J. (1989) High-frequency T-DNA-mediated gene tagging in plants. Proc Natl Acad Sci U S A 86: 8467-8471
Barnes, W. M. (1990) Variable patterns of expression of luciferase in transgenic tobacco leaves. Proc Natl Acad Sci U S A 87: 9183-9187
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