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The full text of this important new paper is available at:
http://dx.plos.org/10.1371/journal.pone.0013684
Possible new twist in GM safety debate
Bristol University
Press release: 27 October 2010
http://www.bristol.ac.uk/news/2010/7279.html
Scientists at the University of Bristol have discovered a previously
unknown route by which GM genes may escape into the natural
environment.
By studying plant-fungi-bacteria interactions at plant wound sites,
the team have identified a natural process stimulated by a hormone
released by the wounded plant that would allow synthetic genes to move
across organisms and out into the wild.
The bacterium Agrobacterium tumefaciens transforms plant tissue as
part of its infection process. This natural process provides an
important toolbox for scientists to genetically manipulate many
species of plants. Recently this technology has been developed for
non-plant organisms including fungi by the Bailey & Foster Group in
Bristol’s School of Biological Sciences.
Their success has come from adding the plant wound hormone
acetosyringone, which triggers Agrobacterium transformation mechanisms
and allows foreign genes to modify cells (genetic transformation). In
the natural environment Agrobacterium and fungi likely encounter each
other at plant wound sites where acetosyringone is present, raising
the possibility of natural gene transfer from bacterium to fungus.
Professor Gary Foster and colleagues tested whether transformation of
fungi by Agrobacterium can occur in nature on plants. Their results
clearly demonstrate that when placed together on damaged plant tissue,
Agrobacterium readily transforms associated fungi. “This suggests a
previously unknown route for horizontal gene transfer in nature,” said
Professor Foster.
These results may have implications for the risk assessment of GM
plants generated via Agrobacterium-mediated transformation.
Agrobacterium can survive within plant tissue following artificial
transformation in tissue culture, and can be detected within
regenerated transgenic plants. This research shows that these
bacteria have the potential to move the same genetic modifications to
fungi in a natural environment.
Prior to release of a GM plant, elimination of Agrobacterium following
modern genetic modification is a key concern of geneticists and policy
makers as it is essential to prevent later escape of synthesised gene
from Agrobacterium to other organisms.
Professor Foster said: “This study suggests that the encounter between
Agrobacterium 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.”
The Bristol study, published online in PLoS ONE, was carried out with
financial support from NERC.
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0013684
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1.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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2.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
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