GM Free Cymru

Crucial Paper 22:
Another route for horizontal gene transfer from GM plants

This is a highly technical, understated but nonetheless important paper which again shows that horizonal gene transfer from GM crops into other living organisms actually happens. Beneath the abstract we reproduce a note from Ignatio Chapela.

Investigating Agrobacterium-Mediated Transformation of Verticillium albo-atrum on Plant Surfaces

Claire J. Knight, Andy M. Bailey, Gary D. Foster* PLoS ONE 5(10): e13684. doi:10.1371/journal.pone.0013684


Agrobacterium tumefaciens has long been known to transform plant tissue in nature as part of its infection process. This natural mechanism has been utilised over the last few decades in laboratories world wide to genetically manipulate many species of plants. More recently this technology has been successfully applied to non-plant organisms in the laboratory, including fungi, where the plant wound hormone acetosyringone, an inducer of transformation, is supplied exogenously. In the natural environment it is possible that Agrobacterium and fungi may encounter each other at plant wound sites, where acetosyringone would be present, raising the possibility of natural gene transfer from bacterium to fungus.

Methodology/Principal Findings

We investigate this hypothesis through the development of experiments designed to replicate such a situation at a plant wound site. A. tumefaciens harbouring the plasmid pCAMDsRed was co-cultivated with the common plant pathogenic fungus Verticillium albo-atrum on a range of wounded plant tissues. Fungal transformants were obtained from co- cultivation on a range of plant tissue types, demonstrating that plant tissue provides sufficient vir gene inducers to allow A. tumefaciens to transform fungi in planta.


This work raises interesting questions about whether A. tumefaciens may be able to transform organisms other than plants in nature, or indeed should be considered during GM risk assessments, with further investigations required to determine whether this phenomenon has already occurred in nature.


Horizontal gene transfer at plant-surface sites

Comment by Ignacio Chapela, Berkeley/Tromsø

The careful and understated presentation, beginning with the title, belies research results that I think should be considered a major landmark in the growing evidence demonstrating how little we know about the ecological consequences of transgenesis, in particular the potential for horizontal gene transfer in real field situations. It also shows a definite and probably very important source of concern, the real possibility that DNA vectored into plants could move out, with full reproductive capacity, via a microbial route into the genomic environment far and beyond the immediate space and phylogeny of the host plant. Any environmental evaluation of field releases should now be required to seriously consider this possibility.

The research for this paper is carefully conceived and conducted, using various sources of confirmatory evidence. The frequency of "spontaneous" transformations out of the bacterium and into the fungus (2 out of 17, 1 out of 15, 10 out of 31 and 14 out of 42 trials in various repetitions) is exceedingly high. Although the paper demonstrates the transfer "only" from whole bacterial cells onto fungal spores (or hyphae), a precautionary approach should dictate that the possibility be also considered that transfers could occur through back-transformation, since much of the Agrobacterium wherewithal necessary to accomplish it is present in the transgenic plant. It is also known that whole Agrobacterium can "hide" through the process of regeneration of plants out of callus in the transgenesis process, providing accessible cells for the transformation, and of course encounters of Agrobacterium and different fungi (and other organisms?) at a plant-wound site must be considered common in the field.

Finally, the authors minimize the possible importance of their findings (perhaps appropriately so, especially to avoid a firestorm over their heads) by suggesting that there should be no biological consequences to the transformation unless the transferred DNA provides some measurable advantage to the carrier fungus. I disagree: We know that there are (a) many examples of apparently "silent" DNA that nevertheless has very important consequences, and (b) many functions of transgenic DNA that may not be predicted by the designs of the people doing the original transformations. DNA does not necessarily need to give an advantage to the carrier; all it needs to do is survive and reproduce. It is unwarranted arrogance to suggest that we know what its functions may be or indeed may become downwind, downtime and down across the phylogenetic landscape.