Science in Society Archive

Killing Fields near You - Terminator Crops at Large

'Terminator technology' makes harvested seeds sterile in order to enforce corporate patents on GM seeds. The public first became aware of the technology in patents jointly owned by US Department of Agriculture and Delta and Pine Land Company, but no one suspected that terminator crops actually exist. ISIS discovered, however, that terminator crops have been field-tested in Europe since 1990, and in the United States since 1992, where several have already been released commercially. The US and UK Governments are now promoting terminator crops as a means of preventing GM genes from spreading. Dr. Mae-Wan Ho, Joe Cummins and Jeremy Bartlett explain why the technology is not only ineffective in preventing gene flow, but introduces extra, potentially fatal hazards. They must be stopped immediately.

Last December, while acting as an expert witness in defence of citizens who have taken action against GM field trials in the UK, MWH discovered that among the crops are AgrEvo's 'male sterile' GM oilseed rape. At the time, we were preparing our submission to a public consultation document, "Guidance on Best Practice in the Design of GM Crops" sent to us by the UK Government's Advisory Committee for Release to the Environment (ACRE). One of the main 'enabling technologies' for 'best practice' - to prevent gene flow - is to engineer seed or pollen sterility.

It soon dawned on us that the GM oilseed rape undergoing field trials have been created using 'terminator technology', so named by critics because it can render harvested seeds sterile in order to enforce corporate patents on GM seeds. AgrEvo's application revealed that such crops have been field-tested in France and Belgium since 1990, and subsequently, in Sweden and Canada, before coming to the UK. We further discovered that similar male sterile lines have been tested in the US at least as early as 1992 and several already released commercially.

The complete terminator system requires two components, the enzyme barnase, which kills the germ cells, and a 'site-specific' recombinase, which is used to block the action of barnase until it is required. There have been 132 field trials of crops with barnase [1], the vast majority without risk assessment. Crops modified for male sterility include rapeseed, corn, tobacco, cotton. Brassica oleracea, potato, poplar, chicory, petunia and lettuce. The USDA commercial release data include 4 crops with barnase: a corn and a canola by AgrEvo, a chicory by Bejo, and another corn by Plant Genetic Systems [2]. Separately, the 'site-specific' recombinase has been engineered into corn and papaya, and there have been 14 field trials between 1994 and 1998, without environmental impact assessment, as it was deemed unnecessary.

There are more than 150 US patents listing barnase or site-specific recombinase or both [3] the oldest going back to 1987. The first terminator patents to catch public attention were those jointly owned by US Department of Agriculture and Delta and Pine Land Company, which Monsanto had intended to acquire. The novelty in those patents is the proposal to combine the barnase with the site-specific recombinase, giving the company complete control over the hybrids as well as proprietary chemicals that control gene expression.

These patents met with universal condemnation world wide, as being contrary to basic human rights. The technology would prevent farmers from saving, replanting and exchanging seeds, practices going back thousands of years that are essential to food security. Monsanto announced it would give up terminator crops, to everyone's relief. Research and development, however, have continued unabated.

At the same time that consultation on best practice is occurring in the UK, the US government is consulting its citizens on the USDA-Delta and Pine patents, which the USDA plans to develop commercially. The USDA is also recommending the technology for preventing gene flow. At the end of January 2001, the USDA signed a deal with Delta and Pine for commercial development to go ahead [4].

Surely, to require containment of GM genes is to admit that they are unsafe, which is a reason for stopping GM crop development altogether, and not for promoting a morally bankrupt technology. Moreover, this technology introduces serious potentially fatal hazards [5] in the genes used. Barnase is a universal poison, while the recombinase can scramble genomes in unpredictable, lethal ways.

Denial or just being kept in the dark?

When confronted by a journalist, a spokesperson from the UK Department of the Environment, Transport and the Regions (DETR) denied that the enzyme barnase is in the crops undergoing field trials. He was reported to have said that the barnase gene, and not the enzyme, was present in "a few oil seed rape crops", and that "where the enzyme would be poisonous, the gene was not harmful."[6] Obviously, he forgot that the barnase gene had to be expressed to make the barnase enzyme in order to cause male sterility.

Dr. Ian Woiwod of Rothampstead, a scientist involved in overseeing the UK field trials, indicated that he had no knowledge of such crops in the field trials [7]. Indeed, a correspondence describing the trials published in Nature [8] made no mention of the male sterile spring and winter oilseed rape. During a workshop at the first meeting of the Intergovernmental Committee on the Cartegena Protocol on Biosafety held in Montpellier last December, a UK Government delegate from the DETR actually thanked MWH for providing the information.

How seed/pollen sterility is engineered into crops

There are two key components to terminator technology. The first component is literally the 'terminator' barnase, an enzyme that breaks down RNA. RNA is an intermediate in the expression of all genes, and that is why barnase is lethal to all cells in which it is expressed. Barnase is specifically inhibited by barstar. Both barnase and barstar are produced by a soil bacterium, Bacillus amyloliquefaciens. Inside the bacterial cell, barstar binds to barnase in a one-to-one complex, disarming the latter so it can do no harm. However, when barnase is secreted outside, it is no longer bound to barstar and is thus harmful to other cells.

The second component is a 'site-specific' recombinase enzyme that recognises specific 'sites', or short DNA sequences, labelled 's' in the diagram below. Any stretch of DNA sequence flanked by two such sites will be spliced out by the recombinase.

To engineer pollen sterility, the barnase gene is placed under the control of a promoter, a gene switch that allows the gene to be expressed only during anther development, ie, in the male part of the flower. The barnase with its anther-specific promoter is stitched next to the transgene of interest, say, a gene coding for herbicide tolerance, also with its own promoter. Theoretically, there will be no fertile pollen from this transgenic crop. In the case of crops that are normally self-fertilised, there will be no seeds set. In out-crossing plants, the only fertile seeds set will be those fertilised by non-GM varieties nearby, which will not be herbicide tolerant; so farmers who want the herbicide tolerant trait will have to buy fresh seeds from the company every season.

The problem is that such a male-sterile line by itself cannot be propagated, it does not breed true. To propagate the line, the 'site-specific' recombinase can be used. For example, the promoter of the barnase could be blocked by a sequence flanked by sites recognised by the recombinase.

The recombinase can be engineered into the same GM line with the barnase gene for male sterility. The recombinase is placed under the control of a promoter that responds to an external chemical, say, the antibiotic tetracycline.

When tetracycline is applied, the recombinase is expressed, and splices out the blocking sequence in the barnase promoter, so barnase is expressed. By treating harvested seed with tetracycline before they are sold to the farmer, the company can ensure that the plants grown from the seeds will be pollen sterile.

If female-sterility is required, the barnase gene could be placed under the control of a promoter that works only during ovule development, ie, in the female part of the flower, and the rest is similar.

Alternatively, the recombinase may be engineered into a GM line with the gene coding for barstar, which, when crossed with the male sterile GM line containing barnase, will produce a hybrid. The hybrid, treated with tetracycline, will produce plants that will still set seed, at least in theory, because the barstar inactivates the barnase. However, if the harvested seeds were re-sowed, the farmer will find that only about half (7/16) [9] of the seeds will have the same characteristics as those originally purchased from the company, and about one fifth (3/16) of the seeds may be completely sterile. It could be considerably worse.

Terminator crops cannot prevent gene flow and introduce extra, potentially fatal hazards

Terminator crops are ineffective for preventing gene flow because

  1. All gene control systems are 'leaky', in the sense of not being 100% accurate; as a result, some fertile pollen/seeds are likely to be produced.
  2. Pollen-sterile GM plants can still be fertilised by non-GM pollen, just as GM pollen from ovule-sterile plants can cross with non-GM plants, thus enabling gene escape.
  3. Terminator crops will not limit horizontal gene transfer, if anything, the complicated constructs involved will enhance it. This is a process whereby the GM DNA is taken up directly into cells of unrelated species and incorporated into the cell's genome.

The genes involved in terminator crops are potentially fatal. Barnase is a potent RNAse that breaks down RNA indiscriminately, and is known to be harmful, if not lethal, to all cells, animals and humans included. When perfused into rat kidneys, barnase causes kidney damage [10]. The 'site-specific' recombinases are known not to be specific. There is already evidence suggesting that genomes can be scrambled by the recombinase (see Note 5). This has now been clearly demonstrated.

The recombinase, Cre, catalyses recombination between two lox sites, splicing out the stretch of DNA in between. When Cre is expressed at high levels in the sperm cells of transgenic mice, the males became 100% sterile, despite the absence of any lox sites [11]. Sterility is caused directly by the recombinase enzyme scrambling the genome, essentially by breaking and rejoining DNA at inappropriate sites on the same or different chromosomes. Embryos fertilised by these sperms arrest predominantly at the 2-cell stage, and do not go beyond the 4-cell stage (see Terminator Recombinase Does Scramble Genomes).

The greatest danger of terminator crops stems from the spread of the genes and constructs, not only to related species by out-crossing but by horizontal transfer to unrelated species. The complication of the GM constructs involved will only increase structural instability, which in turn increases the tendency for the genes to transfer horizontally and recombine. Transfer of both the terminator gene barnase and the recombinase will have drastic, potentially fatal effects on agriculture, biodiversity and health.

These killing crops must be stopped once and for all.

  2. Thanks to Jill Davies for this information
  4. "USDA - Delta & Pine Land Commercialization Agreement Reached, Pollen Transformation System" January 29, 2001 SCOTT,
  5. See "Why patents on life-forms and living processes should be rejected from TRIPS - Scientific briefing on TRIPS Article 27.3(b)" by Mae-Wan Ho And Terje Traavik, TWN and ISIS Report, 1999 ; "Terminator in different guises" ISIS News #3, December 1999 "Terminator gene product alert" ISIS News#6, September 2000
  6. "GM 'poison' allegation denied" .
  7. Personal communication by e-mail to I-SIS from Dr. Ian Woiwod, 8.12.2000.
  8. Firbank, L.G. et al, (1999). Nature 399, 727-8.
  9. It deviates from the usual 9/16 Mendelian ratio for the inheritance of two genes, barnase and barstar. On account of a one-to-one complex between barnase and barstar; plants in which there are two copies of barnase to one copy of barstar will be expected to be partially sterile.
  10. Ilinskaya, O and Vamvakas, S (1997). Nephrotic effect of bacterial ribonucleases in the isolated and perfused rat kidney. Toxicology 120, 55-63.
  11. Schmidt E.E., Taylor, D.S., Prigge, J.R., Barnett, S. and Capecchi, M.R. (2000). Illegitimate Cre-dependent chromosome rearrangements in transgenic mouse spermatids. PNAS 97, 13702-13707.