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[SANET-MG] DAS-59122-7 maize modified for corn rotworm protection
17 March 2007
Prof. Joe Cummins
Professor Emeritus of Genetics University of Western Ontario London,
Canada and The institute of Science in Society , London, UK
738 Wilkins Street
London, Ontario N6C4Z9 Canada
E-email : jcummins@uwo.ca
DAS-59122-7 Maize Genetically Modified for Root Worm Protection and
Herbicide Tolerance
Dow Chemical company and it’s associated company Pioneer Hybrid Seed
Company have developed maize variety Herculex RW for rootworm
protection. The variety is based on the gene transformation event
DAS-59122-7 which express unique binary proteins Cry34Ab1 and Cry35Ab1
derived from the soil bacterium Bacillus thuringiensis (Bt) Herculex.
DAS-59122-7 (59122 for short) also expresses the PAT protein conferring
resistance to the herbicide glufosinate ammonia These transgenes are
inserted at a single locus in a maize chromosome along with control
genes including promoters and terminators (1).
An Application for the Determination of Nonregulated status for BT Cry
34/35Ab1 Insect resistant , Glufosinate Tolerant Corn: Corn Line 59122
was submitted by Dow Agrisciences/Pioneer Hybrid International for
approval by the United States Department of Agriculture Animal and Plant
Health Inspection Service (USDA/APHIS during December 2003 (2). That
report noted that event 59122 had incorporated a synthetic approximation
of the Cry 34Ab1 gene driven by a maize ubiquitin promoter and intron
and terminated using a terminator sequence from potato protease
inhibitor II. A synthetic approximation of the Cry 35Ab1 gene was driven
by a wheat peroxidise promoter and terminated with the terminator from
potato protease inhibitor II A synthetic approximation of the PAT gene
for resistance to glufosinate was driven by the 35S CaMV promoter and
terminated with 35S CaMV terminator. According to the report the genes
were stably inserted at a single locus and there was no evidence of
instability in 59122. The proteins synthesized from the synthetic genes
were compared with proteins synthesized in bacteria and seemed identical
(however later studies showed that the proteins were significantly
different). The main human safety and environmental tests were done on
protein derived from bacteria not the protein products of the synthetic
approximations of the bacterial genes used to transform maize.
USDA/APHIS carried out an environment assessment of maize event 59122.
That assessment included potential impact on non target organisms
including threatened and endangered species. The event was deemed to
have inflicted no significant impact on the environment (3). However,
the bulk of those tests were done with proteins isolated from bacteria (
a less costly procedure than isolating the proteins from transgenic
maize) and those proteins were similar but identical to the proteins
produced in 59122.
A fuller comparison of the insecticidal proteins produced in 59122 with
those in the bacteria producing the proteins used in safety testing
showed that 4 amino acids in the C-terminal protein domain were
different in Cry35Ab1 protein produced in recombinant maize from those
produced in the Cry35Ab1 produced in bacteria and used in safety tests.
These differences were considered negligible (4). In general, the C
terminal domain of Bt toxins is involved in structural stability, ion
channel gating , binding to membrane vesicles and determining
insecticidal specificity (5). A study of Cry34/Cry35 insecticidal
proteins from diverse Bt strains Cry 35Ab1 contains a segment similar to
the to a beta-trefoil domains that may be a binding motif (6). Beta
trefoil domain binds galactose , some examples of trefoil domain include
the toxins from Clostridium botulinum, abrin and ricin (7). It seems
very daring to ignore amino acid sequences in a domain known to be
active in important functions.
Even though most of the earlier regulatory approval had been based on
safety tests with proteins obtained from bacteria rather than from 59122
forage and grain samples from maize 59122 were analysed and compared
with near-isogenic non-GM maize lines to determine whether or not 59211
was substantially equivalent to un-modified maize. The maize lines were
compared for fibre and minerals, for amino acids, fatty acids ,
vitamins, secondary metabolites and anti-nutrients. One parameter,
carbohydrate, was significantly lower in 59122 treated with glufosinate
and along with that finding 13 of 65 determinations including forage
fibre, grain amino acids and vitamins were outside the levels for
conventional maize. In spite of these findings 59122 was deemed
substantially equivalent to unmodified maize (8).
A sub chronic feeding study of rats fed 59122 grain compared with grain
from a near isogenic line for 90 days was followed by study of weight ,
behaviour and organ necropsy. For the most part the differences between
59122 and unmodified maze fed animals were not significantly different.
However, Levels of mean corpuscular haemoglobin, and haemoglobin
concentration, red cell width, reticulocyte count and platelet count
showed significant differences but these blood values were not deemed
significant (9). Chickens were fed grain either from 59122 or from a
near isogenic maize. Carcass and organ weights were measured after 42
days of feeding (there was no extensive necropsy of the organs). For the
most part carcass and organ sizes were not significantly different in
50122 than they were in unmodified maize but the livers of female
chickens were significantly enlarged in the transgenic maize fed animals
. The statistically significant difference in liver weight was not
considered biologically significant by the company researchers(1O).
The novel approach used by company researchers , passing over
significant differences caused by the consumption of 59122 with a few
words of comfort should be a matter of concern to regulators. The
significant differences between 59122 and near isogenic maize lines in
the light of the relatively crude parameters that were measured cries
out for fuller study, The use of proteins produced in bacteria from
natural genes to test the safety of proteins rather than the proteins
produced by synthetic approximations of natural genes such as those used
in 59122 also cries out for fuller study. Presently, a much fuller
safety evaluation of genetically modified maize , such as 59122 can be
achieved using the micro array technology which is available , for
example, maize(11). The use of such advanced technology might improve on
the equivocal results claimed to be evidence that 59122 is safe for
consumption in food and feed.
References
1. The Dow Chemical Company Product Safety Assessment Herculex RW
Rootworm Protection 2006
http://www2.dupont.com/Biotechnology/en_US/products/herculex_rw/safety2.html
2. Hunst.P and Rood,T . Application for the Determination of
Nonregulated Status for Bt Cry34/35 Ab1 insect resistant
Glufosinate-Tolerant Corn: Corn Line 59122 2004
http://www.aphis.usda.gov/brs/aphisdocs/03_35301p.pdf
3. Smith,C. Environment Assessment for Dow/Pioneer Rootworm Resistant
Corn 2005 http://www.aphis.usda.gov/brs/aphisdocs2/03_35301p_com.pdf
4. Gao Y, Schafer BW,Collins RA,Herman RA, Xu X,Gilbert JR,Ni W,Langer V
and Tagliani LA. Characterization of Cry34Ab1 and Cry35Ab1 insecticidal
crystal proteins expressed in transgenic corn plants and Pseudomonas
fluorescens. J Agric Food Chem. 2004 Dec 29;52(26):8057-65
5. Saraswathy,N and Kumar,P. Protein engineering of delta endotoxins of
Bacillus thuringiensis Electronic Journal of Biotechnology Microbial
Biotechnology 2004,2,1-12 DOI: 10.2225/vol7-issue2-fulltext-3
http://www.ejbiotechnology.info/content/vol7/issue2/full/3/index.html
6. Schnepf HE,Lee S,Dojillo J,Burmeister P,Fencil K,Morera L,Nygaard
L,Narva KE and Wolt JD. Characterization of Cry34/Cry35 binary
insecticidal proteins from diverse Bacillus thuringiensis strain
collections. Appl Environ Microbiol. 2005 Apr;71(4):1765-74
7. Mancheno JM, Tateno H, Goldstein IJ, Martinez-Ripoll M and Hermoso
JA. Structural analysis of the Laetiporus sulphureus hemolytic
pore-forming lectin in complex with sugars. J Biol Chem. 2005 Apr
29;280(17):17251-9
8. Herman RA,Storer NP,Phillips AM,Prochaska LM and Windels P.
Compositional assessment of event DAS-59122-7 maize using substantial
equivalence. Regul Toxicol Pharmacol. 2007 Feb;47(1):37-47.
9. Malley LA,Everds NE,Reynolds J,Mann PC,Lamb I,Rood T,Schmidt J,
Layton RJ,
Prochaska LM,Hinds M,Locke M, Chui CF,Claussen F,Mattsson JL and Delaney
B. Subchronic feeding study of DAS-59122-7 maize grain in Sprague-Dawley
rats. Food Chem Toxicol. 2007 Jan 25;In press doi:10.1016/j.fct.2007.01.013
10.
McNaughtona,J,Robertsa,M,Riceb,D,Smith,B,Hindsb,M.Schmidtb,J.Lockec,M,Bryant,A,Rood.T,
Laytonb,R,Lamb,I and Delaneyb,B. Feeding performancenext term in
previous termbroiler chickens fednext term diets containing previous
termDAS-59122-7next term maize grain compared to diets containing
non-transgenic maize grain Animal Feed Science and Technology 2007,132,
227-239
11. Shi,C,Thümmler,F,Melchinger,A,Wenzel,G and Lübberstedt.T. Comparison
of transcript profiles between near-isogenic maize lines in association
with SCMV resistance based on unigene-microarrays Plant Science, 2006,
170,159-169
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