Maize Necrotic Virus - a result of CaMV promoter recombination?

Correspondence

The text below is quite technical. In short we asked if the USDA group for researching corn diseases has tested if the maize necrotic streak virus (MNeSV) might have arisen in GE corn plants through recombination between the CaMV promoter and an infecting virus.

Dr. Peg Redinbaugh, who lead this research, answered that this was not considered as such recombination was not regarded as possible because the viruses are not related.

Dr. Joe Cummins (PSRAST), who is well acquianted with the virus recombination issue, comments that Dr Redinbaugh is mistaken. The recombination "hotspot" in CaMV may give rise to recombination between unrelated viruses.

April 14 (approximately)

Questions sent by PSRAST to Dr. Peg Redinbaugh

(Due to technical error the mail we sent was lost, so the questions were reconstructed from my memory)

1. In your investigation on maize necrotic streak virus (MNeSV), did you check whether it may have been created through recombination with CaMV promoters in genetically engineered corn?

2. In your examination of new viruses do you routinely check the possibility that they may have been created through CaMV promoter recombination?

Jaan Suurkula M.D.
Chairman of PSRAST

April 16 2001

Reply by Dr. Peg Redinbaugh

Dear Dr. Suurkula,

Thanks for your inquiry about maize necrotic streak virus (MNeSV). In answer to your first question, we did not purposely analyze for the possibility that MNeSV arose from recombination between infecting viruses and CaMV containing transgenes, because we had no reason to believe that such recombination would occur.

MNeSV is a positive strand RNA virus. While there is evidence to suggest that there may be recombination among RNA viruses in a plant, this recombination requires a high degree of sequence identity (>80%) between the two viruses. Recombination has been demonstrated in plants between two isolates of the same virus and between two highly related viruses (e.g., two luteoviruses that infect the same plant). There would also be a chance that an infecting virus could recombine with an expressed transgene encoding a highly related viral gene. MNeSV has no close sequence relationship with any known maize-infecting virus, so the probability that it arose from a recent recombination event between two naturally-occurring viruses is remote at best.

It is clear that MNeSV did not, and could not, have arisen from recombination between a maize-infecting RNA virus and CaMV sequences in transgenic plants. There are several reasons for this aside from the fact that MNeSV and CaMV have no sequence similarity. Being a plant RNA virus, MNeSV has no intermediate DNA form. Further, the CaMV DNA sequences used for making transgenic crops are promoter sequences that are not transcribed into RNA. Thus, there is no CaMV RNA in transgenic maize. Because RNA does not recombine with DNA, there is no likelihood that MNeSV genome would recombine with CaMV 35S promoter sequences.

You asked whether we analyze for recombination with CaMV as the source of new viruses. We do not, primarily for the reasons outlined above. That being said, we routinely screen new viral sequences (including MNeSV) for similarity with all of the sequences in GenBank. This screen would give us a clear indication of any type of recombination between existing characterized viruses, including CaMV.

Sincerely,

Peg Redinbaugh

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M.G. Redinbaugh 330-263-3965 (Phone)
USDA, ARS Corn and Soybean Research 330-263-3841 (FAX)
Department of Plant Pathology
OARDC/OSU
1680 Madison Ave.
Wooster, OH 44691

April 18, 2001

Comment by Dr. Joe Cummins

Reply to comments on CaMV by Dr. Redinbaugh

The sense of Dr. Redinbaugh's comments on your question about the CaMV promoter is that since the promotor is not transcribed it cannot possibly participate in recombination with an RNA virus. That view point is ,unfortunately, a narrow one and one that ignores the actual promoter first patented by Monsanto and later improved with enhancer and other elements under separate patents.

The Monsanto patent : US5352605:Chimeric genes for transforming plant cells using viral promoters Fraley; Robert T. , Ballwin, MO Horsch; Robert B. , St. Louis, MO Rogers; Stephen G. , St. Louis, MO Applicant(s): Monsanto Company, St. Louis, MO Includes the untranscribed promoter and a polyadenylation signal that is transcribed but not translated. Downstream of the promoter there is an untranslated leader sequence of great importance.

In DNA the CaMV promoter region is a hot spot for recombination and in the intact virus most recombination has been associated with RNA to DNA reverse transcription. Turning to RNA to RNA recombination in viruses the homology requirement may be specious, particularly one that ignores the leader sequence.

Many times in the past the researchers and journal editors have preferred to consider alternative views about this issue. `Howard Temin the discoverer of retroviruses was a friend of mine and I recollect the difficulty of having clear alternatives considered against science dogma of the time.

In conclusion, the virus group being considered is noted, according to the literature, for actively exchanging blocks of genes. In time interesting gene acquisition may be identified in the virus.

Joseph E. Cummins, Professor Emeritus (Genetics) Dept. of Plant Sciences University of Western Ontario, Canada.