The race towards the first genetically modified plant 

 
 
19 June 2013
 
 

1983 was a great year for plant biology. First, Barbara McClintock was awarded the Noble prize for Physiology for the discovery of genetic transposition in maize. Second, four publications demonstrated the proof of concept of introducing genes into plants and opened the era of agriculture biotechnology. 1-4 The exciting race towards the first transgenic plant, which celebrates its thirtieth anniversary this year, deserves a historical reflection.
 
 
In the 1960s, two young post-doctoral researchers at Ghent University (Belgium) decided to work on plant tumors. Both not keen to use living animals as test systems, they thought they could learn something about animal tumors by studying the tumor-inducing plant pathogen Agrobacterium tumefaciens. Already from the 1940s, many researchers from distinct disciplines showed their interest in Agrobacterium because of its unusual infection process. Although it was already suggested by Armin Braun in that time that bacterial DNA would be the underlying inducer of the typical ‘crown-gall’ plant tumors 5 and although Rob Schilperoort detected Agrobacterium DNA in sterile crown gall tissue cultures 6, it was the Ghent research group headed by Marc Van Montagu and Jeff Schell that discovered the Tumor-inducing plasmid of Agrobacterium.7 Having found an efficient DNA delivery system that would enable plant genetic engineering, a world-wide initiative was launched to unravel the details of the bacterial DNA transfer mechanisms. The race towards the first transgenic plant was declared open.
 
The group around Mary-Dell Chilton joined the race and demonstrated in the 1977 Cell paper that only a part of the Ti-plasmid, i.e. the T-DNA, was integrated into the plant genome.8 The top publications marched swiftly, and the Ghent lab answered in Nature 9 and Science 10 by showing that conserved regions flanking the T-DNA are involved in the integration process. In a very close sprint both groups showed in 1980 that the T-DNA was integrated into the nuclear plant DNA. 11, 12 A next hurdle that had to be taken was the conversion of the Ti plasmid into a gene expression vector. The quest for such a vector was on-going in parallel in Ghent (Van Montagu/Schell), St Louis (Chilton) and in Leiden (Schilperoort). And although it was again the Ghent lab that designed the first non-oncogenic Ti plasmid 13, the Rob Schilperoort group developed the most elegant strategy: a multipurpose vector system in which the T-DNA and the vir genes needed for infection were physically separated 14, a system we still know today as binary vectors. The final step was to generate a vector with an easy selectable marker. A new player (the group of Robert T. Fraley at Monsanto) joined the game and in 1983 the race towards the first (kanamycin-resistant) transgenic plant ended.
 
To know who won the race, one can easily look up the publication dates.1-4 The more important question however is to know who the real winner is. The answer: science and society.
Thanks to the efforts of hundreds of scientists at the dawn of plant genetic engineering, plant scientists received a tool to revolutionize fundamental plant research. Suddenly molecular plant biology was not restricted anymore to knock-out lines. Overexpression lines could be made, mutants could be complemented, tagged versions of favourite proteins could be expressed to in situ follow their localisation and behaviour, and specifically knock-down and/or knock-out strategies could be initiated.
 
Additionally, genetic transformation of plants has put plant breeding on a new level, enabling the fastest development of new agricultural traits in the history of commercial agriculture. 30 years after the proof of concept, more than 170 million hectares of genetically modified crops are grown worldwide, having significant positive effects on environment and society.15
Because of the scientific efforts of those days, we have herbicide-tolerant and insect-resistant crops that since 1996 are responsible for a 9% reduction in pesticide spraying 16, virus-resistant fruits and vegetables, poplars adapted for a bio-based economy, draught-tolerant maize, blight-resistant cisgenic potatoes, aphid-tolerant wheat, provitamin A enriched rice and so many other interesting traits waiting for development and commercialisation.
 
During the coming decades more GM crops will be produced and if integrated in a new agricultural model that combines the best aspects of conventional and organic farming, the huge agricultural hurdles we are facing can be taken with confidence. Looking to the remarkable outcome of the glorious days in the 1970s and 80s, one could start fantasizing that in those days also the foundation was laid for another plant specific Noble prize. One step in that direction has been done: on June 19, Marc Van Montagu, Mary-Dell Chilton and Robert T. Fraley were awarded the World Food Prize 2013.
 

References
1. Bevan M et al 1983. A chimaeric antibiotic resistance gene as a selectable marker for plant cell transformation. Nature 304, 184-187.
2. Fraley et al 1983. Expression of bacterial genes in plant cells. Proc. Natl. Acad. Sci. USA 80, 4803-4807.
3. Hererra-Estrella et al 1983. Expression of chimaeric genes transferred into plant cells using a Ti-plasmid-derived vector. Nature 303, 209-213.
4. Murai N et al 1983. Phaseolin gene from bean is expressed after transfer to sunflower via tumor-inducing plasmid vectors. Science 222, 476-482.
5. Braun AC 1947. Thermal studies on the factors responsible for tumor initiation in crown gall. Am. J. Bot. 34, 234-240.
6. Schilperoort RA et al 1967. Formation of complexes between DNA isolated from tobacco grown gall tumours and RNA complementary to Agrobacterium tumefaciens DNA. Biochim. Biophys. Acta 145, 523-525.
7. Zaenen I et al. 1974. Supercoiled circular DNA in crown gall inducing Agrobacterium strains. J. Mol. Biol. 86, 109-127.
8. Chilton M-D et al. 1977. Stable incorporation of plasmid DNA into higher plant cells : the molecular basis of crown gall tumorigenesis. Cell 11, 263-271.
9. De Picker A et al. 1978. Homologous DNA sequences in different Ti-plasmids are essential for oncogenicity. Nature 275, 150-153.
10. Zambryski P et al. 1980. Tumor DNA structure in plant cells transformed by A. tumefaciens. Science 209, 1385-1391.
11. Chilton M-D et al. 1980. T-DNA from Agrobacterium Ti plasmids is in the nuclear DNA fraction of crown gall tumor cells. Proc. Natl. Acad. Sci. USA 77, 4060-4064.
12. Willmitzer L et al. 1980. The Ti-plasmid derived T-DNA is present in the nucleus and absent from plastids of plant crown-gall cells. Nature 287, 359-361.
13. Zambryski P et al. 1982. Tumor induction of Agrobacterium tumefaciens: analysis of the boundaries of T-DNA. J. Mol. Appl. Genet. 1, 361-370.
14. Hoekema A et al 1983. A binary plant vector strategy based on separation of vir- and T-region of the Agrobacterium tumefaciens Ti-plasmid. Nature 303, 179-180.
15. James C 2012. Global status of commercialized biotech/GM crops. ISAAA Brief No 44.
16. Brookes G and Barfoot P 2012. Global impact of biotech crops: Environmental effects, 1996-2010. GM Crops and Food: Biotechnology in Agriculture and the Food Chain 3, 129-137.