Organic Consumers Association

OCA
Homepage

Previous Page

Click here to print this page

Make a Donation!

JOIN THE OCA NETWORK!

GE Trees Will Spread Mutant, Allergenic Pollen Over Long Distances

February 21, 2005
"Preventing flowering in transgenic trees"
Professor J Cummins jcummins@UWO.CA

Transgenic (genetically modified, GM) trees are beginning to flood
the ecosystems of the world. The modified trees have been tested
extensively in large open plots with little concern over the spread of
genes from the plots. Dispersal of pollen and seeds from forest trees
has been extensively investigated. Reviews of such studies show that
gene flow transport may be measured in kilometers (1,2). It is very
clear that the transgenes from GM trees cannot be contained on a
plantation and they will spread widely. For that reason a great deal of
effort has been devoted to developing molecular genetic modifications
that will prevent flowering or pollen production. Unless fool proof
methods for controlling flower or pollen production are proven
commercial development of transgenic trees is out of the question.
For the most part, the methods used to control flowering or pollination
involved interfering with the genetic program for floral development or
for deleting cells involved in floral development, Before reviewing
the various flower control projects for forest trees it might be
helpful to briefly examine the genes controlling flowering. A group of
genes called MADS-box genes code for transcription factors that
recognize DNA binding domains (the MADS-box) and recognize similar
target DNA sequences that determine developmental pathways. The MADS
genes associated with flowering have to be identified then modified to
control flowering or pollination. The plant MADS genes are related to
animal homeotic (HOX) genes that are extensively studied regulators of
morphogenesis(3). Unraveling the functions of MADS genes has allowed
flower development to be manipulated.

Flowering is prevented by either by controlling gene product formation
using anti-sense genes or by using small regulatory RNA to prevent
active gene products such as the MADS box transcription factor from
being formed or by genetic ablation using a toxin gene driven by a
floral gene promoter.. The preferred toxin gene to be employed is the
barnase ribonuclease from the bacterium Bacillus amylolquefaciens. That
ribonuclease is activated using a promoter specific to floral or pollen
development. The gene effectively kills the cells that it targets.
Another cell death toxin used is the diphtheria toxin from the
bacterium Cornyebacterium diphtheria or related ADP-Ribosyltransferase
toxins form other bacteria but those toxin gene are used less than the
barnase gene. The preferred barnase gene is a part of the genetic
construction called ³terminator² that has been developed to control
corporate seed production (5).

Professor Steven Strauss of Oregon State University pioneered flower
and pollen control in poplar. He and his colleagues have led in the
area of flowering control in forest trees. Strauss pointed out that
when completer floral sterility is achieved will require vegetative
propagation (6). Floral sterility has begun to be extended from poplar
to shade trees (7). Strauss has argued that management of GM poplar is
comparable to conventional poplar even though he is well aware of the
seed and pollen dispersal with transgenic poplar (8). Along with the
exploration of floral sterility Strauss has investigated speeding
flower development (trees normally take years to develop sexually) to
allow rapid breeding and selection cycles.(9). Of course the rapid
breeding cycle is fraught with uncertainty about the mature tree.
Strauss has introduced use of the poplar homologue to the floral MADS
box genes , the poplar promoter gene PTD(10). The PTD promoter was
combined with the diphtheria toxin gene, DTA, to produce sterile polar
without the detrimental effects on yield encountered earlier (11). The
problem of somaclonal variation is hardly mentioned in the discussion of
flower control in poplar even though the problem was discussed in a
report on a four year field trial of herbicide tolerant poplar reported
by the Strauss group (12). Somaclonal variation results from the cell
culture technique used to select and propagate transgenic plants. It
results in extremely high levels of mutation and chromosome instability
which could reverse floral sterility. Earlier reports showed that
poplar cell culture resulted in extremely high levels of somaclonal
variation(13,14).

In Finland investigators from Sopanen University have studied the
control of flowering in silver birch. Those investigators identified the
MADS box genes controlling flowering in the birch tree (15,16). When a
flower specific birch promoter gene BpMADS1 was used to drive the
barnase gene floral cell ablation prevented flowering but there were
marked side effects effecting leaves and branching (17). The side
effects were likely a pleiotrophic effect of the gene insertion but
could, as well have been effected by somaclonal variation from cell
culture. A recent report altered the name of the MADS box gene from
BpMADS to BpFULL1 as in the previous study flowering was prevented but
the gene modification effected leaves and branching (18). The
pleiotrophic effects observed may extend into areas not yet detected
and they require more extensive study.

Before leaving the discussion of the control of flowering in trees it
may be useful to consider the potential side effects of the ablation
toxins used to create sterile trees. Barnase ribonuclease proved toxic
to the kidneys of rats (19) Barnase was cytotoxic in mice and in
human cell lines (20). Animals may not find the GM forests welcoming.
Diphtheria toxin has been associated with anaphylactic response (221)
As the song goes: ³If you go down in the (transgenic) woods today,
You're sure of a big surprise.² The safety of transgenic forest should
be carefully evaluated before the trees are widely dispersed.

References
1.DiFazio,S,Slavov,G,Burczyk,J,Leonardi,S. and Strauss,S. Gene flow from
tree plantations and implications for transgenic risk assessment 2004
Plantation Forest Biotechnology for the 21st Century eds. Walter,C. and
Carson,M. 405-22
2. Slavov,G,DiFazio,S. and Strauss,S. Gene flow from forest trees: from
empirical estimates to transgenic risk assessment 2002 Scientific
methods workshop: ecological and agronomic consequences of gene flow
from transgenic crops to wild relatives Columbus,Ohio
3.Ng,M. and yanofsky,M. Function and evolution of the plant MADS ­Box
gen family 2001 Nature Reviews Genetics 2,186-96
4.Skinner,J,Meilan,M, Brunner,A. and Strauss,S. Options for genetic
engineering of floral sterility in forest trees 2000 Jain,S. and
Minocha,S. eds Molecular Biology of Woody Plants Kluwer Academic
publishers Netherlands
5.Ho,M. and Cummins,J. 2001 Terminate the terminators!
http;//www.i-sis.org.uk/
6Strauss,S,Rottman,W,Brunner,A. and Sheppard,L. Genetic engineering of
reproductive sterility in forest trees 1995 Molecular Breeding 1, 5-26
7.Brunner,A,Mphamed,R,Meilan,R,Sheppard,L, Rottman,W. and Strauss,S.
Genetic engineering of sexual sterility in shade trees 1998 J.
Arboculture 24, 263-73
8. Strauss,S.,DiFazio,S. and Meilan,R. Genetically modified poplars in
context 2001 The Forestry Chronicle 77,271-80
9. Strauss, S., and Brunner, A. Tree biotechnology in the 21st century:
Transforming trees in the light of comparative genomics.(2004). In S.H.
Strauss and H.D. Bradshaw (Eds.), The BioEngineered Forest: Challenges
to Science and Society, Pp 76-97. Resources for the Future, Washington,
D.C., USA.
10. Meilan,R.Brunner,A,Skinner,J. and Strauss,S. Modification of
flowering transgenic trees 2001 eds. Morohoshi,M. and Komamine,A. eds
Molecualr Breeding of Woody Plants Elsevier Science B.V. 247-57
11. Skinner,J,Meilan,R,Ma,C. and Strauss,S. The poplar PTD promoter
imparts floral predominant expression and enables high levels of floral
organ ablation in Populus, Nicotiana and Arabidopsis² 2003 Molecular
Breeding 12,119-32
12. Meilan,R,Auerbach,D,Ma,C.,DiFazio,S. and Strauss,S. Stability of
herbicide resistance and GUS expression in transgenic hybrid poplars
during four years of ffield trials and vegetative propagation Hort.Sci.
37,277-80
13. Antoneti,L. and Pinon,J. Somaclonal variation within poplar 1993 Plant
Cell ,Tissue and Organ culture 35,99-106
14. Wang, G., Castiglione, S., Chen, Y., Li, L., Han, Y. and Tian, Y.
Poplar (Populus nigra L.) plants transformed with a Bacillus
thuringiensis toxin gene:
insecticidal activity and genomic analysis 1996 Transgenic Res. 5, 289­301
15. Lemmetyinen,J,Hassinen,M,Elo,A,Porali,I,Keinonen,K,Makela,H. and
Sopanen,T. Functional characterization of SEPALLATA3 and AGAMOUS
orthologues in silver birch 2004 Physiologia Plantarum 121,149-62
16. Lannenpa,M,Janonen,I,Holtta-Vuor,M,Gardemeister,M,Porali,I. and
Sopanen,T. A new SBP-box gene BpSPL1 in silver birch (Betula pendula)
2004 Physiologia Plantarum 120,491-500
17. Lemmetyinen,J,Keinonen,K. and Sopanen,T. Prevention of the flowering
of a tree, silver birch 2004 Molecular Breeding 13,243-9
18. Lännenpää,M,Ranki,A,Hölttä-Vuori,M,Lemmetyinen,J,Keinonen,K. and
Sopanen,T. Prevention of flower development in birch and other plants
using a pFULL1::BARNASE construct 2005 Plant Cell Reports in press doi
10.1007/s00299-004-0903-y
19. Ilinskaya,O. and Vamvakas,S. Nepherotoxic effects of bacterial
ribonuclease in the isolated perfused rat kidney 1997 Toxicology 120,55-63
20. Prior,T, Kunwar,S. and Pastan,I. Studies on the activity of barnase
toxins in vitro and in vivo 1996 Bioconjugate Chemistry 7,23-9
21.Rosenberg,A. Immunogenicity of biological therapeutics: a hierarchy
of concerns 2003 Developmental Biology 112,15-21

****************************************************************************
****************************
This GMO news service is underwritten by a generous grant from the Newman's
Own Foundation, edited by Thomas Wittman and is a production of the
Ecological Farming Association www.eco-farm.org <http://www.eco-farm.org/>
****************************************************************************
****************************