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2-Plants: GE canola genotype can be modified by pathogen invasion

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TITLE:  A) Comment of Natural Law Party Wessex
        B) Plants rendered herbicide-susceptible by cauliflower
           mosaic virus-elicited suppression of a 35S promoter-
           regulated transgene
SOURCE: A) NLP Wessex, UK,
        B) Nature Biotechnology, Vol. 18 (9), pp. 995 - 999
           by Al-Kaff et al.
DATE:   A) August 31, 2000
        B) September 2000

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The scientific abstract (below) just released in the September 2000 
edition of scientific journal 'Nature Biotechnology' is going to 
cause some interesting discussion.

What this study found is that oilseed rape genetically modified to be 
resistant to a herbicide lost that resistance when it encountered a 
naturally occurring environmental pathogen (the Cauliflower Mosaic 
Virus). In other words had the farmer sprayed this rape in the field 
with the recommended herbicide the oilseed rape would have been 
killed as well as the weeds - not quite the idea of this technology!

This could lead to some interesting crop loss claims by farmers 
against biotech companies if it happened on a large enough scale in 
the field.

The Cauliflower Mosaic Virus (CaMV) is a common pathogen of brassicas 
(cabbage, caulifower, rape etc). In this case genetically modified 
rape which became infected by it (a common occurrence with brassica 
crops) lost its resistance to the herbicide. The relevant gene 
conferring herbicide resistance appears to have become switched off. 
The herbicide in this case is bialaphos.

Such 'gene silencing' has previously been considered to result from 
an interaction between the invading environmental pathogen and the 
viral 'promoter' (itself taken from the CaMV) which is used to 
artificially fire up the foreign transgene in the first place. This 
particular viral promoter is used in most transgenic crops, into 
whose every cell it is embedded.

This study is particularly interesting as it concerns the bialaphos 
herbicide which is related to glufosinate-ammonium, the herbicide to 
which most of the crops in GM fieldscale trials in the UK have been 
developed by Aventis to have resistance. It would appear that the 
same transgene provides resistance to glufosinate-ammonium as to 
bialaphos (see footnote). How comfortable would most UK farmers feel 
about this if they knew about it (or for that matter Aventis's 
shareholders and insurers)?

The use of the CaMV 35s promoter in most transgenic crops is one of 
the most controversial technical aspects of the use of GM in 
agriculture. The risks associated with it go well beyond the 'gene 
silencing' apparently demonstrated in this case. For more information 
on those risks see:

This particular paper abstract from Nature Biotechnology finishes 
with the words: "Our results show that transgene phenotypes can be 
modified by pathogen invasion".

In other words the characteristics of genetically modified crops may 
change when they are released into the environment and interact with 
naturally occurring pathogens such as viruses. It is interesting that 
this should be reported in the scientific literature literally years 
after the large scale introduction of these types of crop into the 
environment around the world, particularly when such introduction has 
been based on insistence from scientists and regulators that they 
know what they are doing and everything has been fully tested. Draw 
your own conclusions!

This latest paper on the subject was produced by scientists at the 
John Innes Centre which is an advisor to the UK government on safety 
aspects of GM crops. The JIC previously commented on such gene-
silencing phenomena in a paper published in 1998 as follows:

".....Recent research in our laboratory with Brassica napus plants 
containing the 35S promoter from the mosaic virus (CaMV) has shown 
that upon infection with the CaMV the driven transgene is silenced 
(Al-Kaff et al unpublished). Intensive research at present is 
directed towards understanding this silencing mechanism and its 

As the 35S promoter is widely used to regulate transgenics in 
brassicas, it is important that we strive to obtain a clear 
understanding of the mechanisms of this silencing and its 
significance. This is important for two reasons, for assessing the 
use of the 35S promoter in agriculture and also for assessing the 
significance of this effect for biosafety. The presence of homology 
between the 35S promoter and the infecting virus is clearly important 
in determining this silencing phenomenon ....

A knowledge of transgene stability, expression and inheritance is 
fundamental for the successful and safe use of transgenes in large 
scale agricultural production. Many factors influence the ways in 
which transgenes express, but a factor of crucial importance is the 
effect of DNA sequences that are homologous to areas of transgene 
constructs. For those concerned with the development of transgenic 
brassicas the take home message from this paper is 'watch out for 
homology' ". [emphasis added]

As the JIC commented in a further paper in 1998:

"One of the most challenging issues associated with assessing the 
environmental impact of transgenic plants when in widespread 
commercial production are scale dependent effects. It is possible 
that a rare event may have insignificant consequences when transgenic 
crops are grown on a small experimental scale, but become more 
important when transgenic crops are grown over thousands of 

Meanwhile this material continues to be released into the UK 
environment in the form of the UK fieldscale trials and commercial 
crops in other parts of the world.


*Bialaphos [L-2-amino-4-((hydroxy)methyl) (phosphinoyl)-butyryl-L-
alanyl-L-alanine] is a commercially available natural phytotoxin. 
Glufosinate-ammonium [Ammonium-DL-homoalanin-4-yl(methyl)-phosphinic 
acid] is the synthetic version of bialaphos' herbicidal moiety, 

It appears that the same transgene provides resistance to glufosinate-
ammonium as to bialaphos:


Plants rendered herbicide-susceptible by cauliflower mosaic virus-
elicited suppression of a 35S promoter-regulated transgene

Nadia S. Al-Kaff, Maria M. Kreike, Simon N. Covey, Robert Pitcher, 
Anthony M. Page & Philip J. Dale
John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, UK.
Correspondence should be addressed to N S Al-Kaff. e-mail:

Crop plants genetically modified for herbicide tolerance were some of 
the first to be released into the environment. Frequently, the 
cauliflower mosaic virus (CaMV) 35S promoter is used to drive 
expression of the herbicide tolerance transgene. We analyzed the 
response to CaMV infection of a transgenic oilseed rape line 
containing the bialaphos tolerance gene (BAR) from Streptomyces 
hygroscopicus, regulated by the 35S promoter.

Oilseed rape is susceptible to CaMV, but plants recover from 
infection. CaMV infection altered the expression of the herbicide 
tolerance gene such that plants became susceptible to the herbicide. 
The effect on transgene expression differed in infections with viral 
pathogenic variants typical of those found in natural situations 
worldwide. Susceptibility to the herbicide was most likely a result 
of transcriptional gene silencing of the transgene. Our results show 
that transgene phenotypes can be modified by pathogen invasion.


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