Regulators Discover a Hidden Viral Gene in Commercial GMO Crops

Regulators Discover a Hidden Viral Gene in Commercial GMO Crops





by Jonathan Latham and Allison Wilson
How should a regulatory agency announce they have discovered
something potentially very important about the safety of products they
have been approving for over twenty years?

In the course of analysis to identify potential allergens in GMO
crops, the European Food Safety Authority (EFSA) has belatedly
discovered that the most common genetic regulatory sequence in
commercial GMOs also encodes a significant fragment of a viral gene (Podevin and du Jardin 2012).
This finding has serious ramifications for crop biotechnology and its
regulation, but possibly even greater ones for consumers and farmers.
This is because there are clear indications that this viral gene (called
Gene VI) might not be safe for human consumption. It also may disturb
the normal functioning of crops, including their natural pest
resistance.

Cauliflower Mosaic Virus

What Podevin and du Jardin discovered is that of the 86 different
transgenic events (unique insertions of foreign DNA) commercialized
to-date in the United States 54 contain portions of Gene VI within them.
They include any with a widely used gene regulatory sequence called the
CaMV 35S promoter (from the cauliflower mosaic virus; CaMV). Among the
affected transgenic events are some of the most widely grown GMOs,
including Roundup Ready soybeans (40-3-2) and MON810 maize. They include
the controversial NK603 maize recently reported as causing tumors in
rats (Seralini et al. 2012).

The researchers themselves concluded that the presence of segments of
Gene VI “might result in unintended phenotypic changes”. They reached
this conclusion because similar fragments of Gene VI have already been
shown to be active on their own (e.g. De Tapia et al. 1993). In other
words, the EFSA researchers were unable to rule out a hazard to public
health or the environment.

In general, viral genes expressed in plants raise both agronomic and human health concerns (reviewed in Latham and Wilson 2008).
This is because many viral genes function to disable their host in
order to facilitate pathogen invasion. Often, this is achieved by
incapacitating specific anti-pathogen defenses. Incorporating such genes
could clearly lead to undesirable and unexpected outcomes in
agriculture. Furthermore, viruses that infect plants are often not that
different from viruses that infect humans. For example, sometimes the
genes of human and plant viruses are interchangeable, while on other
occasions inserting plant viral fragments as transgenes has caused the
genetically altered plant to become susceptible to an animal virus
(Dasgupta et al. 2001). Thus, in various ways, inserting viral genes
accidentally into crop plants and the food supply confers a significant
potential for harm.

The Choices for Regulators
The original discovery by Podevin and du Jardin (at EFSA) of Gene VI in
commercial GMO crops must have presented regulators with sharply
divergent procedural alternatives. They could 1) recall all CaMV Gene
VI-containing crops (in Europe that would mean revoking importation and
planting approvals) or, 2) undertake a retrospective risk assessment of
the CaMV promoter and its Gene VI sequences and hope to give it a clean
bill of health.

It is easy to see the attraction for EFSA of option two. Recall would
be a massive political and financial decision and would also be a huge
embarrassment to the regulators themselves. It would leave very few GMO
crops on the market and might even mean the end of crop biotechnology.

Regulators, in principle at least, also have a third option to gauge
the seriousness of any potential GMO hazard. GMO monitoring, which is
required by EU regulations, ought to allow them to find out if deaths,
illnesses, or crop failures have been reported by farmers or health
officials and can be correlated with the Gene VI sequence.
Unfortunately, this particular avenue of enquiry is a scientific dead
end. Not one country has carried through on promises to officially and
scientifically monitor any hazardous consequences of GMOs (1).

Unsurprisingly, EFSA chose option two. However, their investigation
resulted only in the vague and unreassuring conclusion that Gene VI
“might result in unintended phenotypic changes” (Podevin and du Jardin
2012). This means literally, that changes of an unknown number, nature,
or magnitude may (or may not) occur. It falls well short of the solid
scientific reassurance of public safety needed to explain why EFSA has
not ordered a recall.

Can the presence of a fragment of virus DNA really be that
significant? Below is an independent analysis of Gene VI and its known
properties and their safety implications. This analysis clearly
illustrates the regulators’ dilemma.

The Many Functions of Gene VI
Gene VI, like most plant viral genes, produces a protein that is
multifunctional. It has four (so far) known roles in the viral infection
cycle. The first is to participate in the assembly of virus particles.
There is no current data to suggest this function has any implications
for biosafety. The second known function is to suppress anti-pathogen
defenses by inhibiting a general cellular system called RNA silencing
(Haas et al. 2008). Thirdly, Gene VI has the highly unusual function of
transactivating (described below) the long RNA (the 35S RNA) produced by
CaMV (Park et al. 2001). Fourthly, unconnected to these other
mechanisms, Gene VI has very recently been shown to make plants highly
susceptible to a bacterial pathogen (Love et al. 2012). Gene VI does
this by interfering with a common anti-pathogen defense mechanism
possessed by plants. These latter three functions of Gene VI (and their
risk implications) are explained further below:

1) Gene VI Is an Inhibitor of RNA Silencing
RNA silencing is a mechanism for the control of gene expression at the
level of RNA abundance (Bartel 2004). It is also an important antiviral
defense mechanism in both plants and animals, and therefore most viruses
have evolved genes (like Gene VI) that disable it (Dunoyer and Voinnet
2006).

Gene VI (upper left) precedes the start of the 35S RNA

This attribute of Gene VI raises two obvious biosafety concerns: 1)
Gene VI will lead to aberrant gene expression in GMO crop plants, with
unknown consequences and, 2) Gene VI will interfere with the ability of
plants to defend themselves against viral pathogens. There are numerous
experiments showing that, in general, viral proteins that disable gene
silencing enhance infection by a wide spectrum of viruses (Latham and
Wilson 2008).

2) Gene VI Is a Unique Transactivator of Gene Expression
Multicellular organisms make proteins by a mechanism in which only one
protein is produced by each passage of a ribosome along a messenger RNA
(mRNA). Once that protein is completed the ribosome dissociates from the
mRNA. However, in a CaMV-infected plant cell, or as a transgene, Gene
VI intervenes in this process and directs the ribosome to get back on an
mRNA (reinitiate) and produce the next protein in line on the mRNA, if
there is one. This property of Gene VI enables Cauliflower Mosaic Virus
to produce multiple proteins from a single long RNA (the 35S RNA).
Importantly, this function of Gene VI (which is called transactivation)
is not limited to the 35S RNA. Gene VI seems able to transactivate any
cellular mRNA (Futterer and Hohn 1991; Ryabova et al. 2002). There are
likely to be thousands of mRNA molecules having a short or long protein
coding sequence following the primary one. These secondary coding
sequences could be expressed in cells where Gene VI is expressed. The
result will presumably be production of numerous random proteins within
cells. The biosafety implications of this are difficult to assess. These
proteins could be allergens, plant or human toxins, or they could be
harmless. Moreover, the answer will differ for each commercial crop
species into which Gene VI has been inserted.

3) Gene VI Interferes with Host Defenses
A very recent finding, not known by Podevin and du Jardin, is that Gene
VI has a second mechanism by which it interferes with plant
anti-pathogen defenses (Love et al. 2012). It is too early to be sure
about the mechanistic details, but the result is to make plants carrying
Gene VI more susceptible to certain pathogens, and less susceptible to
others. Obviously, this could impact farmers, however the discovery of
an entirely new function for gene VI while EFSA’s paper was in press,
also makes clear that a full appraisal of all the likely effects of Gene
VI is not currently achievable.

Is There a Direct Human Toxicity Issue?
When Gene VI is intentionally expressed in transgenic plants, it causes
them to become chlorotic (yellow), to have growth deformities, and to
have reduced fertility in a dose-dependent manner (Ziljstra et al 1996).
Plants expressing Gene VI also show gene expression abnormalities.
These results indicate that, not unexpectedly given its known functions,
the protein produced by Gene VI is functioning as a toxin and is
harmful to plants (Takahashi et al 1989). Since the known targets of
Gene VI activity (ribosomes and gene silencing) are also found in human
cells, a reasonable concern is that the protein produced by Gene VI
might be a human toxin. This is a question that can only be answered by
future experiments.

Is Gene VI Protein Produced in GMO Crops?
Given that expression of Gene VI is likely to cause harm, a crucial
issue is whether the actual inserted transgene sequences found in
commercial GMO crops will produce any functional protein from the
fragment of Gene VI present within the CaMV sequence.

There are two aspects to this question. One is the length of Gene VI
accidentally introduced by developers. This appears to vary but most of
the 54 approved transgenes contain the same 528 base pairs of the CaMV
35S promoter sequence. This corresponds to approximately the final third
of Gene VI. Deleted fragments of Gene VI are active when expressed in
plant cells and functions of Gene VI are believed to reside in this
final third. Therefore, there is clear potential for unintended effects
if this fragment is expressed (e.g. De Tapia et al. 1993; Ryabova et al.
2002; Kobayashi and Hohn 2003).

The second aspect of this question is what quantity of Gene VI could
be produced in GMO crops? Once again, this can ultimately only be
resolved by direct quantitative experiments. Nevertheless, we can
theorize that the amount of Gene VI produced will be specific to each
independent insertion event. This is because significant Gene VI
expression probably would require specific sequences (such as the
presence of a gene promoter and an ATG [a protein start codon]) to
precede it and so is likely to be heavily dependent on variables such as
the details of the inserted transgenic DNA and where in the plant
genome the transgene inserted.

Commercial transgenic crop varieties can also contain superfluous
copies of the transgene, including those that are incomplete or
rearranged (Wilson et al 2006).
These could be important additional sources of Gene VI protein. The
decision of regulators to allow such multiple and complex insertion
events was always highly questionable, but the realization that the CaMV
35S promoter contains Gene VI sequences provides yet another reason to
believe that complex insertion events increase the likelihood of a
biosafety problem.

Even direct quantitative measurements of Gene VI protein in
individual crop authorizations would not fully resolve the scientific
questions, however. No-one knows, for example, what quantity, location
or timing of protein production would be of significance for risk
assessment, and so answers necessary to perform science-based risk
assessment are unlikely to emerge soon.

Big Lessons for Biotechnology
It is perhaps the most basic assumption in all of risk assessment that
the developer of a new product provides regulators with accurate
information about what is being assessed. Perhaps the next most basic
assumption is that regulators independently verify this information. We
now know, however, that for over twenty years neither of those simple
expectations have been met. Major public universities, biotech
multinationals, and government regulators everywhere, seemingly did not
appreciate the relatively simple possibility that the DNA constructs
they were responsible for encoded a viral gene.

This lapse occurred despite the fact that Gene VI was not truly
hidden; the relevant information on the existence of Gene VI has been
freely available in the scientific literature since well before the
first biotech approval (Franck et al 1980). We ourselves have offered
specific warnings that viral sequences could contain unsuspected genes (Latham and Wilson 2008).
The inability of risk assessment processes to incorporate longstanding
and repeated scientific findings is every bit as worrysome as the
failure to intellectually anticipate the possibility of overlapping
genes when manipulating viral sequences.

This sense of a generic failure is reinforced by the fact that this
is not an isolated event. There exist other examples of commercially
approved viral sequences having overlapping genes that were never
subjected to risk assessment. These include numerous commercial GMOs
containing promoter regions of the closely related virus figwort mosaic
virus (FMV) which were not considered by Podevin and du Jardin.
Inspection of commercial sequence data shows that the commonly used FMV
promoter overlaps its own Gene VI (Richins et al 1987). A third example
is the virus-resistant potato NewLeaf Plus (RBMT-22-82). This transgene
contains approximately 90% of the P0 gene of potato leaf roll virus. The
known function of this gene, whose existence was discovered only after
US approval, is to inhibit the anti-pathogen defenses of its host
(Pfeffer et al 2002). Fortunately, this potato variety was never
actively marketed.

A further key point relates to the biotech industry and their
campaign to secure public approval and a permissive regulatory
environment. This has led them to repeatedly claim, firstly, that GMO
technology is precise and predictable; and secondly, that their own
competence and self-interest would prevent them from ever bringing
potentially harmful products to the market; and thirdly, to assert that
only well studied and fully understood transgenes are commercialized. It
is hard to imagine a finding more damaging to these claims than the
revelations surrounding Gene VI.

Biotechnology, it is often forgotten, is not just a technology. It is
an experiment in the proposition that human institutions can perform
adequate risk assessments on novel living organisms. Rather than treat
that question as primarily a daunting scientific one, we should for now
consider that the primary obstacle will be overcoming the much more
mundane trap of human complacency and incompetence. We are not there
yet, and therefore this incident will serve to reinforce the demands for
GMO labeling in places where it is absent.

What Regulators Should Do Now
This summary of the scientific risk issues shows that a segment of a
poorly characterized viral gene never subjected to any risk assessment
(until now) was allowed onto the market. This gene is currently present
in commercial crops and growing on a large scale. It is also widespread
in the food supply.

Even now that EFSA’s own researchers have belatedly considered the
risk issues, no one can say whether the public has been harmed, though
harm appears a clear scientific possibility. Considered from the
perspective of professional and scientific risk assessment, this
situation represents a complete and catastrophic system failure.

But the saga of Gene VI is not yet over. There is no certainty that
further scientific analysis will resolve the remaining uncertainties, or
provide reassurance. Future research may in fact increase the level of
concern or uncertainty, and this is a possibility that regulators should
weigh heavily in their deliberations.

To return to the original choices before EFSA, these were either to
recall all CaMV 35S promoter-containing GMOs, or to perform a
retrospective risk assessment. This retrospective risk assessment has
now been carried out and the data clearly indicate a potential for
significant harm. The only course of action consistent with protecting
the public and respecting the science is for EFSA, and other
jurisdictions, to order a total recall. This recall should also include
GMOs containing the FMV promoter and its own overlapping Gene VI.

Footnotes
1) EFSA regulators might now be regretting their failure to implement
meaningful GMO monitoring. It would be a good question for European
politicians to ask EFSA and for the board of EFSA to ask the GMO panel,
whose job it is to implement monitoring.


Source:-
http://independentsciencenews.org/commentaries/regulators-discover-a-hidden-viral-gene-in-commercial-gmo-crops/