|Sweet potatoes. Photo Creative Commons|
Analysis of the genome of the sweet potato revealed stable incorporation of functional DNA from a possibly ancestral species of bacterial plant pathogen, Agrobacterium rhizogenes. No such horizontal gene transfer was detected in wild relatives.
Sweet potato is one of the oldest domesticated crops and has been found in archaeological remains dating back 8,000-10,000 years.
Infection by Agrobacterium rhizogenes induces root proliferation. A related bacterium, Agrobacterium tumefaciens, afflicts orchards and vineyards where it induces galls (plant tumours). Because it invades and alters the plant genome, GM versions of A. tumefaciens are widely used to insert artificial DNA into plant cells.
The ancient pathogen DNA incorporated into the sweet potato was found to be expressing itself at very low levels, but no functional role was obvious.
What's interesting is the indication that human intervention seems to have resulted in pathogenic elements becoming sequestered in crop plants under human protection. Wild relatives appear more genetically robust and self-preserving.
The existence of sequestered viral DNA has long been known, and the possibility of its re-activation due to human molecular manipulation of genomes has long been a concern. It now seems this may also be a consideration in the case of bacterial elements in the genomes of domesticated crops. Physiological disruption or novel plant diseases could emerge in either case and lead to crop failure. Both such disturbances could also induce the production of novel toxins in the plant.
In the case of modern genetic engineering, the created DNA routinely combines both viral and bacterial sequences. This compounds concerns regarding harmful interactions between natural and artificial DNA. Note that the GM potatoes which Arpad Pusztai suspected of causing problems in his rat feeding studies due to the inserted DNA itself (not the gene product) contained both Agrobacterium tumefaciens and viral DNA elements; no follow-up studies were possible due to the abrupt termination of the project by government and the scientific establishment.
Co-evolution of sweet potatoes and humans over thousands of years has ensured that any damaging qualities emerging in a crop have been expunged because the initially limited community of people eating them wouldn't survive to continue the cultivation of the problem. We have, of course, no way of knowing if any of these ancient Agrobacterium rhizogenes infected sweet potatoes caused ill-health.
The paper could have concluded that GM crops should be tested for the presence and activation of sequestered pathogen DNA, and that rigorous steps should be taken to protect the centre of origin of crop species to preserve their purity.
Instead, each summary and discussion section ends with the idea that sweet potatoes are "naturally transgenic" and that somehow this could affect the current consumer distrust of GM safety. The suggestion was enthusiastically taken up by pro-GM scientists and reporters.
Bearing in mind that horizontal gene transfer has been known about for decades, and Agrobacterium's ability to invade hosts with its own genes is what makes it a plant pathogen, it's difficult to see why the finding of ancient Agrobacterium genes in a plant is such a big deal. The events of several thousand years ago must have started on a small scale and spread slowly through domesticated crops because it seems they aren't active enough to cause physiological disruption or to reduce fitness.
Any suggestion that this finding is comparable with the use of GM Agrobacterium to insert an artifical DNA construct containing an aggressive 'on' switch attached to genes which have been specially adapted to their new host, is neither scientific nor sensible. Ignoring the difference between a gradual infiltration of low-activity genes over millenia and the whole-sale insertion of over-active DNA sequences into plants introduced overnight into millions of hectares is breathtakingly irrational.
As genetics professor, Jack Heinemann, said
"Of course nature can also create organisms - by (horizontal gene transfer) or other means - that are capable of causing us harm. But that is no reason for us to do it unwittingly to ourselves."The authors, their peer reviewers and the journal editor seem only too happy to publish a 'scientific' study with blatant pro-commercial-GM propaganda tacked on. If you're having trouble making sense of this blatant abuse of science, check out THE CULTURE OF NEATLY SIMPLE SCIENCE - July 2015.
- Tina Kyndt, et al., May 2015, The genome of cultivated sweet potato contains Agrobacterium T-DNAs with expressed genes: An example of a naturally transgenic food crop, PNAS 112
- Sweet potato genetically engineered by nature - or spin worthy of Goebbels? GM Watch 6.05.15
- Mae-Wan Ho, et al., 1999, Cauliflower Mosaic Viral Promoter - A Recipe for Disaster? Microbial Ecology in Health and Disease 11