GE Trees Will Spread Mutant, Allergenic Pollen Over Long Distances

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.


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tree plantations and implications for transgenic risk assessment 2004
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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

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4.Skinner,J,Meilan,M, Brunner,A. and Strauss,S. Options for genetic
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7.Brunner,A,Mphamed,R,Meilan,R,Sheppard,L, Rottman,W. and Strauss,S.
Genetic engineering of sexual sterility in shade trees 1998 J.
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during four years of ffield trials and vegetative propagation Hort.Sci.

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2004 Physiologia Plantarum 120,491-500

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toxins in vitro and in vivo 1996 Bioconjugate Chemistry 7,23-9

21.Rosenberg,A. Immunogenicity of biological therapeutics: a hierarchy
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