Science in Society Archive

New Terminator Crops Coming

Gaining control over seed production using ‘terminator’ genetic modification has become a goal of genetic engineers. Prof. Joe Cummins and Dr. Mae-Wan Ho alert us to some new tricks in the pipelines.

Engineering seed control can guaranteed patent protection over a particular crop and help to prevent transgene escape and contamination of non-GM crops, at least in theory. Controlling pollen fertility also allows the development of hybrid seeds that may have ‘hybrid vigor’ (heterosis) over non-hybrids, again, at least in theory.

We have reviewed many ‘terminator’ systems [1-5], genetic modifications that produce crops with infertile seeds or inactive pollen, and warned of the problems and hazards involved. But development of such systems continues apace, as GM proponents and governments alike have been promoting them as means of preventing or restricting transgene escape, which is highly misleading.

One system under development involves regulating a nuclear gene in oilseed rape (Brassica rapa) that controls pollen development. The gene Br DAD1 encodes an enzyme that catalyzes the first step in the synthesis of jasmonic acid, a growth-regulator. The absence of jasmonic acid leads to inviable pollen. The Br DAD1 gene is down-regulated with an anti-sense gene to Br DAD1.

This system facilitates the production of hybrid seeds by seed companies. The hybrid, sold to farmers, will definitely contain the anti-sense transgene as well as antibiotic resistance marker gene(s) used in making the GM plant, so there is no transgene containment at all.

For perpetuating the GM line, the down-regulated plant can be restored to fertility with a timely spray of jasmonic acid [6], a registered plant growth-regulator. So, after spraying, the plant will again be spreading the anti-sense transgene and antibiotic resistance marker gene(s).

The other problem is that the anti-sense Br DAD1 gene is at a locus separate from BrDAD1. Hence, the fertility of the crop will also be influenced by recombination and segregation.

A second newly developed system for controlling seed production is more similar to the original terminator system. It involves a repressible seed-lethal system designed to prevent novel transgenic traits from spreading.

The system starts with a GM plant hemizygous - carrying a single copy of a gene on one of a pair of chromosomes - for a seed-lethal gene cassette tightly linked to the transgene coding for the novel trait (SN/-). This is crossed with a plant homozygous - carrying two copies of a gene, one on each of a pair of chromosomes - for a repressor R that can turn off the seed-lethal gene (R/R).

If SN and R are each on one of the same pair of chromosomes, the resulting F1 hybrid will be seed-fertile, though half of the offspring is SN/R and the other half -/R. However, if selection is applied to select for the novel trait – which may be tolerance to a particular herbicide - only SN/R plants will survive. In practice, a farmer will have to sow twice as many seeds to achieve the density of plants required.

If the F1 plants (SN/R) is self-pollinated, half of the F2 plants will be SN/R, one quarter will be SN/SN and one quarter R/R. Applying the selection for the novel trait will leave only the first two types of plants. If replanted, then one third of the seeds will be sterile.

In addition, both the SN/R plants and SN/SN plants will still produce pollen, which can cross-pollinate with non-GM varieties. Presence of the SN construct in the contaminated seed will result in failure to germinate, thereby terminating the contamination if grown in the field. But those contaminated with R will still be fertile. Thus, non-transgenic crops will still be contaminated, and in addition, the germination rate of the non-transgenic seeds will also be compromised.

If genetic recombination has occurred in the F1 plants so that SN and R end up on the same chromosome, then the contamination of non-transgenic crops will be much more extensive and will perpetuate. Thus, this containment system, too, is worse than useless.

Seed-sterility has been created using Agrobacterium tumefaciens genes to overproduce the plant hormone indole acetic acid (IAA or auxin) by a pathway not normally found in plants [7]. Plants have two other pathways to convert tryptophan to IAA [8], and the seed containment system introduces a third.

Introducing genes and pathways that cause accumulation of tryptophan or its metabolites in the seeds or tissues of crop plants deserves special safety considerations. Such crops cannot be deemed "substantially equivalent" without extensive testing on animals and human volunteers. Tryptophan produced in a genetically modified bacterium was linked to an epidemic called eosinophilia myalgia syndrome in 1989. Thousands were permanently injured and one or more impurities were thought to be responsible for the illness [9]. Elevated levels of 5-hydroxy IAA, a brain indole, were found in patients dying from liver injury [10], and are associated with cell injury in mammals.

It is clear that these new terminator technologies cannot prevent transgenes from spreading, while their safety is questionable. They serve no other purposes than to exert control over seed production - forcing farmers to buy hybrid seeds that cannot be replanted - and to protect patented traits.

Article first published 12/07/03



References

  1. Ho MW and Cummins J. Chronicle of an Ecological Disaster Foretold . ISIS Report, 20 February 2003 ; also Science in Society 2003, Spring, 18 , 26-27.
  2. Ho MW. Terminator technologies in new guises. ISIS News 3 , December 1999, ISSN: 1474-1547 (print), ISSN: 1474-1814 (online)
  3. Cummins J. Terminator gene product alert. ISIS News 6 , September 2000, ISSN: 1474-1547 (print), ISSN: 1474-1814 (online)
  4. Ho MW, Cummins J and Bartlett J. Killing fields near you. Terminator crops at large. ISIS News 7/8 , February 2001, ISSN: 1474-1547 (print), ISSN: 1474-1814 (online)
  5. Ho MW and Cummins J. Terminator patents decoded. ISIS News 11/12 , October 2001, ISSN: 1474-1547 (print), ISSN: 1474-1814 (online)
  6. Hatakeyama K, Ishiguro S, Okada K, Takasaki T and Hinata K. Antisense inhibition of a nuclear gene , Br DAD1, in Brassica causes male sterility, that is restorable with jasmonic acid treatment. 2003 Molecular Breeding 2003, 11, 325-36
  7. Schernthaner J, Fabijanski S, Arnison P, Racicot M and Robert L. Control of seed germination in transgenic plants based on the segregation of a two-component genetic system. PNAS 2003, 100, 6855-59.
  8. Cohen J, Slovin J and Hendrickson A. Two genetically discrete pathways convert tryptophan to auxin: more redundancy in auxin biosynthesis" Trends in Plant Sciences 2003, 8, 197-8.
  9. Sternberg E. Pathogenesis of L-tryptophan eosinophilia myalgia syndrome. Adv. Exp. Med. Biol. 1996, 398, 325-30
  10. AlMardini H, Harrison E, Ince P, Barlett K and Record C. Brain indoles in human hepatic encephalopathy. Hepatology 1993, 17,1033-40.

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