Science in Society Archive

Eating Cauliflower Mosaic Virus infected vegetables does not prove that that Cauliflower Mosaic Virus Promoter in genetically modified crops is safe

Prof. Joe Cummins

Recently researchers from the John Innes Centre (JIC) for plant research in Great Britain have again claimed that the Cauliflower Mosaic Virus (CaMV) promoter used to genetically modify virtually all of the transgenic crops now marketed or being tested for marketing has been proven to be safe for human consumption because humans have been consuming virus infected crucifers for a long time. It is worth pointing out that virus infected crucifers are not tasty items and they are avoided by most animal predators including humans. JIC may be exceptional in consuming large quantities of virus infected crops and certainly those laboring at the institute are worthy of fuller study. Even if virus infected crucifers could be prepared and consumed as dietary treats the fact is that the behavior and potential hazard of the CaMV promoter in transgenic crops is unrelated to the replication and behavior of the virus in the plant cell. It is simply unreasonable to maintain that the the integrated CaMV promoter in transgenic crops behaves the same way in the virus replication cycle as it does in the chromosome of the transgenic crop.

CaMV is a pararetrovirus which means that it transmitted as a double stranded DNA virus that replicates using reverse transcription of RNA into DNA. The replication of CaMV is similar to the replication of a related pararetrovirus Hepatitis B (Seeger and Mason 2000). In CaMV replication the infecting virus enters the plant cell then transfers a copy of the viral DNA to the plant cell nucleus where it forms a nuclear plasmid that very rarely (possibly never) integrates into the chromosome. The viral DNA is transcribed releasing both messenger RNA for making virus components and RNA copies of the viral chromosome that are translocated to the cytoplasm where the RNA copies of the viral chromosome are packaged in virion like particles. Within the virion like particles the RNA is reverse transcribed to make the viral DNA that is released from the plant cell in the mature virus (reviewed in Poogin et al 1998).

When CaMV genes are inserted into the DNA of the plant chromosome those genes may recombine with infecting CaMV virus. Wintermantel and Schoelz (1996) found that recombination was observable in every plant when virus invaded transgenic plants with CaMV genes inserted on plant chromosome. They believed that most observed recombination occurred in the cytoplasm during reverse transcription and that there was little chance for recombination between invading virus and CaMV transgenes on the chromosome. Genes such as human interferon have been inserted in CaMV virus and were found to produce interferon in virion like particles but the human genes were not reported to have recombined with plant chromosomesDeZoeten et al (1989).Plant gene replacement vectors based on CaMV have been discussed for nearly twenty years but have not proven highly useful because the only small DNA inserts have proven feasible but recently Viapana et al (2001) have experienced improved success by employing helper virus.

Earlier we discussed the problems with CaMV promoter integrated into the chromosome in great detail.' We pointed out that the CaMV 35S promoter is promiscuous in function, and works efficiently in all plants, as well as green algae, yeast and E. coli. It has a modular structure, with parts common to, and interchangeable with promoters of other plant and animal viruses. It also has a recombination hotspot, flanked by multiple motifs involved in recombination, and is similar to other recombination hotspots including the borders of the Agrobacterium T DNA vector most frequently used in making transgenic plants'(Cummins et al 2000).

In conclusion , authorities from JIC base their belief in the safety of CaMV promoter in transgenic crops on their belief that people and animals massively consume virus infected crops without apparent discomfort. The natural history of CaMV replication in plants clearly shows that the CaMV promoter installed in crop chromosomal DNA is entirely different from CaMV virus replication so that the presumed safety of eating CaMV in crops has no real bearing on the safety of genetically engineered crops with CaMV promoter. In fact JIC seems to be suffering from 'tunnel vision' and directing research away from the real problems with crop genetic technology. The JIC argument surely impresses science administrators and government bureaucrats who, unfortunately, control research funding and gullible journalists who influence public opinion. Even though the discussion between us and JIC has grown repetitious ultimately the inappropriateness of the JIC pronouncements will be widely recognized and then progress can be made in judging the safety of transgenic crops with CaMV promoter.

Article first published 18/02/01



References

  1. Cummins,J,Ho,M and Ryan,A 'Hazardous CaMV promoter?'2000 Nature Biotechnology 18, 363 DeZoeten,G,Penswick,J,Horisberger,M,Ahl,P,Schultze,P and Hohn,T 'The expression,localization and effect of human interferon in plants' 1989 Virology 172,213-22
  2. Poogin,M,Hohn,T and Futterer,J 'Forced evolution reveals the importance of short open reading frame A and secondary structure in the cauliflower mosaic virus 35S RNA leader' 1998 J. Virology 72,4157-69
  3. Seeger,C and Mason,W ' Hepatitis B Virus Biology' 2000 Microbiology and Molecular Biology Reviews 64,51-68
  4. Viaplana,R,Turner,D andCovey,S 'Transient expression of a GUS reporter gene from cauliflower mosaic virus replacement vectors in the presence and absence of helper virus' 2001 J Gen Virol 82,59-65
  5. Wintermantel,W and Schoetz,J 'Isolation of recombinant viruses between cauliflower mosaic virus and a viral gene in transgenic plants under conditions of moderate selection pressure' 1996 Virology 223,156-64

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