1.Horizontal gene transfer at plant-surface sites - comment by Ignacio Chapela
2.Bacteria spread genes to fungi on plants
3.Abstract: Investigating Agrobacterium-Mediated Transformation of Verticillium albo-atrum on Plant Surfaces
NOTE: For the full text of this important new paper: http://dx.plos.org/10.1371/journal.pone.0013684
University of Bristol press release: http://bit.ly/bezdRp
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1.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.
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2.Bacteria spread genes to fungi on plants
Tom Marshall
Planet Earth, 27 October 2010
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013684
A bacterium that's used to modify plants' genes can also change the DNA of completely different lifeforms in the wild, new research shows.
If the bacteria come into contact with particular fungi at a wound in a plant's outer skin, the fungi can come away with new genes from the bacterium. If these help it survive, they could become a permanent part of its genetic makeup.
This is a way genes could potentially escape genetically-modified organisms (GMOs) and move into other living things. It underscores the need to make sure these microbes are removed completely from genetically-modified plants before they leave the lab. It also shows that genes can move between organisms in more ways than has previously been assumed.
'This study suggests that the encounter between this bacterium and a fungus on the plant surface may lead to gene flow in a previously overlooked way, potentially leaking GM genes into the natural world,' says Professor Gary Foster of the University of Bristol, one of the study's authors.
Agrobacterium tumefaciens is a bacterium that in the wild infects plants through wounds in their outer skin and transfers its own genetic material into them, making them form what are called 'crown galls'.
Scientists already know which bit of the bacterium's DNA gets transferred to the new host when it's infected. Removing this DNA and adding new genetic material from another source is the main tool they've used to genetically modify plants like soya beans or oilseed rape to give them desired characteristics like resistance to pesticides or higher vitamin content.
'Agrobacterium is the industry standard for getting new DNA into plants,' says Dr Andy Bailey, a plant pathologist at the University of Bristol who took part in the research. 'It infects many different plants in the wild and effectively carries out natural genetic engineering. But our work raises the question of whether its host range is wider than we had thought - maybe it's not confined only to plants after all.'
To transfer DNA to a plant, Agrobacterium needs a wound in the plant's skin, as well as a hormone called acetosyringone, which plants make when they're injured.
Researchers already knew the bacterium can transform the DNA of living things other than plants, including fungi - whether inserting its own genes, or any others it's provided with. But until now they've had to supply the acetosyringone themselves to make this happen.
In this new research, published in the open-access journal PLoS ONE, Claire Knight, the University of Bristol PhD student on the project, used lab-grown plant samples to show that there is enough acetosyringone around a naturally-occurring wound on a plant to let the bacterium transfer genes to the common fungal pest Verticillium albo-atrum.
In most cases this won't be a problem, as the new genes won't do anything to help the fungus survive. But in particular cases, it's potentially harmful, transferring genes that confer pesticide resistance or some other valuable trait to a harmful pest species.
Companies that produce commercial GM crops already use antibiotics to remove Agrobacterium after it's done its work. But Bailey says this research suggests they may need to do more to ensure this is working. 'If a plant is still carrying Agrobacterium and is planted out, not only other plants but also fungi could receive the new DNA,' Bailey says. 'So it's important to be absolutely certain all the Agrobacterium has been removed.'
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3.Investigating Agrobacterium-Mediated Transformation of Verticillium albo-atrum on Plant Surfaces
Claire J. Knight, Andy M. Bailey, Gary D. Foster*
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013684
Abstract
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.
Conclusions/Significance
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.
*School of Biological Sciences, University of Bristol, Bristol, United Kingdom