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 January 2001 | |
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January 2001 | |
IN THIS ISSUE:
World Agricultural Biotechnology Highlights of 2000
Genetically Modified Crops and Foods: AMA Report
Can "Stealth" Approaches Defeat GISMOS?
Fungicidal Potatoes
Crop Scientists Report Research Headway on FHB Grain Disease
Biotech Feeds Undetectable in Food Products
Insecticides to Target Insect Life Cycle
WORLD AGRICULTURAL BIOTECHNOLOGY HIGHLIGHTS OF 2000
The year 2000 was replete with headline news and controversy for
agricultural biotechnology. With tens of thousands of news stories breaking
over the last twelve months, here is a selection of important ones that have had
a direct effect on the field of agbiotechnology and its public image. January
Meeting in Montreal, delegates from 138
countries reached an agreement on an International Biosafety Protocol to help protect the environment and ensure
the safe transfer, handling, and use of living modified organisms (LMOs)
resulting from modern biotechnology. They signed the Cartagena Protocol on Biosafety
to the Convention on Biological Diversity (http://www.biodiv.org/biosafe/Protocol/Protocol.html). The Protocol is designed to ensure that trade in LMOs does
not have a negative impact on biodiversity and the world's ecosystems. February
Tony Blair, the UK Prime Minister, acknowledged that genetically modified
foods are potentially damaging to human health and the environment. The
Prime Minister said the jury was still out on the new food technology and that there
was legitimate cause for public concern. However, his government remained
fully committed to field trials and to exploring agbiotechnology's potential.
Genetically modified cotton officially became the most popular genetically
altered US crop, largely free from the controversy surrounding modified corn
and soybeans. March
Scientists based at the Swiss Federal Institute of Technology in Zurich
reported they had inserted three genes into rice that resulted in increasing its
beta-carotene content. Researchers claimed that beta-carotene enhanced rice could
help alleviate the serious problem of vitamin A deficiency in developing countries.
Supermarket chain Iceland announced that as of September 2000, suppliers
to Iceland must certify that their meat is obtained only from animals fed
conventional feed, i.e., containing no GE corn or soy ingredients, and urged
the industry's larger companies to follow its lead.
A genetically engineered strain of rice that could boost yields by up to 35%
was developed by US scientists. The new crop was unveiled in the Philippines at
an international conference on rice technology. Rice is part of
the staple diet of a third of the world's people, and the
researchers believe their new product could play a major role in
combating hunger. The plant was engineered by Maurice Ku and
colleagues at Washington State University and by agricultural researchers
in Japan, and has been tested in China, Korea, and Chile (See
ISB News Report, May 2000
Members of the Scottish Parliament backed the Scottish Executive's precautionary approach to introducing genetically modified crops and food, despite calls to make the country a GM-free zone. Health Minister Susan Deacon told the Parliament that it was not realistic for Scotland to turn its back on GM developments.
The European Union's highest court ruled that France did not
have the right in 1998 to suspend approval of three GM maize
strains already cleared at EU level. France originally submitted an
application for EU approval of GM maize on behalf of Swiss
life sciences group Novartis. Once EU approval had been granted,
the government declined to give the final go-ahead, and referred
the matter to the Luxembourg-based European Court of Justice.
April
A report issued by the US National Academy of Sciences'
National Research Council concluded that, according to
currently available evidence, GM foods presently on the market are safe
to eat, and any health and environmental risks posed by GM
and conventionally bred crops are indistinguishable. According to
NAS Committee chair Perry Adkisson of Texas A&M
University, "...we believe it is the properties of a genetically modified
plant—not the process by which it was produced—that should be
the focus of risk assessments."
The European Parliament rejected an EU law amendment that would have made GM producers legally responsible for any damage caused by their products to public health or to the environment. Instead, the Parliament called on the European Commission to devise a more general plan by the end of the year that would still include some liability rules.
Elisabeth Sickl, Austrian minister in charge of food safety and inspection, said that Austria had banned imports of Aventis' GM maize on the grounds that there were no available studies on the long-term impact the crop would have on the environment. She added, "Austria is no laboratory and it is of utmost concern that we maintain Austria as a provider of produce of the highest quality for the whole European market."
In the final days of April, it was revealed that thousands of
hectares of land in the UK and Europe were accidentally
contaminated by GM oilseed rape supplied by Canadian-based Advanta Seeds.
May
Advanta, an Anglo-Swedish firm, admitted selling
ordinary rapeseed mixed with genetically modified seed to farmers
in Sweden, France, Germany, and Britain. The firm said
the amount of GM seed in the oilseed rape crops was
small. Advanta Seeds spokesman David Buckeridge said,
"In Germany and France in particular we are talking
about hundreds of hectares in an area of millions of hectares."
Commercialization of "vitamin A rice" became a step closer to reality when an agreement was reached between GM rice inventors and the biotech companies Zeneca and Greenovation. The companies agreed to distribute the rice seed at no extra cost to farmers in developing countries.
The US Food and Drug Administration (FDA)
announced plans to refine its regulatory approach regarding
foods derived through the use of modern biotechnology.
The initiatives stemmed in part from input received
during FDA's public outreach meetings held late last year
and were built upon programs already underway at FDA to
help ensure the safety of all foods.
June
Research published in Nature
Biotechnology indicated that transgenic maize engineered to express avidin protein
was resistant to insect pest attack during grain storage. Avidin
is a glycoprotein found in chicken egg whites that
sequesters biotin. Maize expressing avidin at levels of 100 ppm
precipitated a biotin deficiency toxic to the insect pests. The
avidin maize was not, however, toxic to mice when
administered as the sole component of their diet for 21 days. The
results suggest that avidin expression in food or feed grain
crops can be used as a biopesticide against a spectrum of
stored-produce insect pests. (Kramer KJ, et al. 2000.
Transgenic avidin maize is resistant to storage insect pests.
Nature Biotechnology 18(6): 670-674.)
The Organization for Economic Cooperation and
Development (OECD) called for developed countries to reach
a consensus on common risk assessment rules for GM
foods and feeds. "There are differences in risk analysis
among OECD countries and some countries have raised
concerns about the adequacy of existing test methods," the
29-member OECD said. The OECD further stated that an
international agreement should be reached on test methods on the
safety of GM products and that continued dialogue was needed
to reach mutual understanding on risk assessment.
July
Greek Agriculture Minister Georgios Anomeritis told
a news conference that Greece would destroy GM
cotton crops after conducting additional testing to determine
the extent of their distribution. Initial tests showed that
GM seeds were mixed in with cotton planted this year,
despite an EU ban on genetically altered cotton. Anomeritis
stated, "After the results of more detailed tests...any cotton
found to be genetically engineered will be uprooted. The
farmers will be completely compensated."
According to a Friends of the Earth Scotland survey, a majority of Scottish local authorities banned the use of GM ingredients in their school meals. The study revealed that 25 of the country's 32 authorities have insisted that GM products be taken off the menu.
The International Society for Plant Molecular Biology Board of Directors unanimously voted to endorse the AgBioWorld "Declaration in Support of Agricultural Biotechnology." The Declaration was drafted by Professor C. S. Prakash at Tuskegee University and signed by 2,700 scientists including James Watson, Gurdev Khush, Hilary Koprowski, Bruce Ames, and Ingo Potrykus. (http://www.agbioworld.org)
August
Marks & Spencer claimed to be the first food retailer
to insist that GM soya and maize ingredients be
removed from livestock feed, a move predicted to force food
prices higher by 15% and test public demand for non-GM food.
A 3 km self-guided walking trail was opened to the
public at Birkbank Farms, Ontario, Canada where visitors
could stroll among the crops, including genetically
engineered sweet corn and potatoes, and garner a better
understanding of the trade-offs and technologies involved in
commercial fruit and vegetable production.
A farm ministry spokeswoman reported that Italy's Cabinet suspended the marketing of four unidentified varieties of GM maize amid concerns over possible health and environmental risks. She added that, "Prime Minister Giuliano Amato blocked the four GM maize varieties as a precautionary step."
September
Experts reacted to information on transgene silencing
in plants engineered with the 35S promotor, as reported in
an article authored by Nadia Al-Kaff. (Al-Kaff NS, et
al. 2000. Plants rendered herbicide-susceptible by
cauliflower mosaic virus-elicited suppression of a 35S
promoter-regulated transgene. Nature
Biotechnology 18: 995-999.) In this research, the cauliflower mosaic virus 35S
promotor was used for expression of the gene that provides
herbicide tolerance. When the virus infected the
transgenic plants, they reacted by methylating the 35S
promotor, which in turn silenced the herbicide tolerance gene
and rendered the plant sensitive to the herbicide. In theory
this could have great consequences for all transgenic
plants using the 35S promotor.
Greenpeace said it was "delighted" with the acquittal of 28 members charged in connection with destroying GM crops. The defendants were cleared of theft and criminal damage charges after facing two trials in six months relating to the destruction on a Norfolk, UK farm last year.
EU farm ministers were divided over how fast to clear new GM crops and still maintain public confidence already battered by a series of health scandals. France, as EU president, was trying to build a consensus around a cautious position on GM crops. However, at an informal meeting of EU farm ministers, France was criticized by several member states for being "too defensive."
An environmental lobby coalition, Genetically Engineered Food Alert, reported some taco shells tested by Genetic ID, a testing company in Fairfield, Iowa, contained traces of the GM corn StarLink, which is not approved for human consumption. StarLink expresses the gene for Cry9C pesticide obtained from Bt. The discovery led to the withdrawal of millions of taco shells from supermarkets and restaurants.
Charles Arntzen, who leads a team of plant scientists
at Cornell University, announced the development of
tomatoes and bananas genetically modified to contain the hepatitis
B vaccine. Hepatitis B is a precursor of liver cancer and
is considered the biggest single cause of cancer deaths.
October
A US federal judge dismissed a lawsuit filed by critics
of agricultural biotechnology who want the government
to require labels on foods containing ingredients derived
from genetically engineered crops.
At the World Food Prize Symposium on biotech foods
in Des Moines, Iowa, a US FDA official told participants
that biotech foods pose fewer health risks because GE
methods produce less genetic alteration than traditional
hybridization techniques. "When you are dealing with biotech crops,
you are changing just one or two genes of the plant's
structure. With hybridization, there are more genes involved and
more uncertainty," said Dr. Bernard Schwetz, acting
Deputy Commissioner, FDA.
November
Scientists, concerned that GM corn pollen landing
on milkweed may be contributing to monarch butterfly
larvae deaths, reported finding more of the weed than
they expected growing around GE crops on farms.
However, the studies did not show any increase in risk to the
Monarch when compared to conventional spraying methods.
The British arm of McDonald's Corp., the world's number one restaurant group, announced it had asked its suppliers to find sources of animal feed that did not contain GM products. They added that it would be impossible to demand a complete ban on GM feeds since non-GM corn and soya meal was not available in sufficient quantities.
December
New GM foods will be licensed for use in the EU
beginning in February 2001, following a deal struck by
Euro-MPs in Strasbourg. Clearance for more than a dozen
GM crops is on hold at Commission headquarters in
Brussels pending updated EU licensing laws not due in force
until 2003. The European Parliament gave its approval to
the new laws, provided that licenses are granted to
companies that agree to abide by the new rules before they
become legally binding.
Scientists finished the first genetic map of Arabidopsis thaliana, a groundbreaking achievement that could herald a new green revolution. Media reports said that the sequencing of the nearly 26,000 genes in Arabidopsis may provide a blueprint for a greater understanding of all plants.
Shane Morris and Doug Powell
Centre for Safe Food
University of Guelph
morris@uoguelph.ca
GENETICALLY MODIFIED CROPS AND FOODS:
The American Medical Association Council on
Scientific Affairs recently issued a summary report after
reviewing the technology used to produce transgenic crops
and examining the issues relevant to the utilization of
transgenic crops and genetically modified foods, including the
current regulatory framework, possible human health
effects, potential environmental impacts, and other
consumer-related issues. The findings and recommendation of
the Council were present on their Web site on December
12, 2000. (
http://www.ama-assn.org/ama/pub/article/2036-3604.html
)
The Council reviewed eleven reports issued over the
last two years by various scientific and governmental bodies
on selected aspects of genetically modified crops.
Additionally, literature searches were conducted in the
MEDLINE database and Lexis/Nexis GenMed library for
relevant articles published between 1990 and September
2000. References containing information relevant to the
safety, regulation, and environmental impact of transgenic
crops and foods were examined further as well as
additional references culled from the bibliographies of these
pertinent references.
Findings
Conclusions
Recommendations
• Federal regulatory oversight of agricultural biotechnology
should continue to be science-based and guided by
the characteristics of the plant, its intended use, and
the environment into which it is to be introduced, not by
the method used to produce it, in order to facilitate
comprehensive, efficient regulatory review of new GM
crops and foods.
• The AMA supports efforts for the systematic safety
assessment of genetically modified foods and
encourages: (a) development and validation of
additional techniques for the detection and/or assessment
of unintended effects; (b) continued use of methods
to detect substantive changes in nutrient or toxicant
levels in GM foods as part of a substantial equivalence
evaluation; (c) development and use of alternative
transformation technologies to avoid utilization of antibiotic
resistance markers that code for clinically relevant
antibiotics, where feasible; and (d) that priority should be given
to basic research in food allergenicity to support
the development of improved methods for identifying
potential allergens.
• The AMA supports continued research into the potential
consequences to the environment of GM crops
including the: (a) assessment of the impacts of
pest-protected crops on nontarget organisms compared to impacts
of standard agricultural methods, through rigorous
field evaluations; (b) assessment of gene flow and its
potential consequences including key factors that regulate
weed populations; rates at which pest resistance genes
from the crop would be likely to spread among weed and
wild populations; and the impact of novel resistance traits
on weed abundance; (c) implementation of
resistance management practices and continued monitoring of
their effectiveness; and (d) development of
monitoring programs to assess ecological impacts of
pest-protected crops that may not be apparent from the results of
field tests.
• The AMA recognizes the many potential benefits
offered by GM crops and foods, does not support
a moratorium on planting genetically modified crops,
and encourages ongoing research developments in
food biotechnology.
• The AMA recognizes that the government, industry, and
the scientific and medical communities have a
responsibility to educate the public and improve the availability
of unbiased information on genetically modified crops
and of research activities.
The full report can be accessed at:
http://www.ama-assn.org/ama/pub/article/2036-3604.html.
CAN "STEALTH" APPROACHES DEFEAT GISMOS?
Tim Hall and his research group helped pioneer
plant transformation by expressing the bean seed
protein phaseolin in tobacco, a dicot plant. In seeking
to broaden the scope of his research to include
monocot transformation, he became aware of the difficulty
in obtaining reliable expression using naked DNA
in physical transformation techniques for rice. His
group is currently gaining insight to silencing
mechanisms and ways to avoid them.
The beneficial application of recombinant biotechnology
to improve agronomic properties of major crops is
well exemplified by advances made in rice. In a recent article
in
ISB News Report (December, 2000
A report of the AMA Council on Scientific Affairs
More than 40 transgenic crop varieties have been
cleared through the federal review process with enhanced
agronomic and/or nutritional characteristics or one or
more features of pest protection (insect and viruses) and
tolerance to herbicides. The most widely used transgenic
pest-protected plants express insecticidal proteins derived
from the bacterium Bacillus thuringiensis (Bt). Crops
and foods produced using recombinant DNA techniques
have been available for fewer than 10 years and no
long-term effects have been detected to date. These foods
are substantially equivalent to their conventional
counterparts. Genetic engineering is capable of introducing allergens
into recipient plants, but the overall risks of introducing
an allergen into the food supply are believed to be similar to
or less than that associated with conventional
breeding methods. The risk of horizontal gene transfer from plants
to environmental bacteria or from plant products consumed
as food to gut microorganisms or human cells is
generally acknowledged to be negligible, but one that cannot
be completely discounted. Pest-resistance due to exposure
to Bt-containing plants has not occurred to date, and
harmful effects on nontarget organisms, which have been
detected in the laboratory, have not been observed in the
field. Nevertheless, these and other possible
environmental effects remain areas of concern.
Federal regulatory oversight of agricultural
biotechnology should be science-based. Methods to assure the safety
of foods derived from GM crops should continue to be
refined and improved. Although no untoward effects have
been detected, the use of antibiotic markers that encode
resistance to clinically important antibiotics should be avoided
if possible. Genetic modification of plants could
potentially lead to detrimental consequences to the
environment. Therefore, a broad-based plan to study
environmental issues should be instituted. There is no scientific
justification for special labeling of genetically modified foods, as
a class, and voluntary labeling is without value unless it
is accompanied by focused consumer education.
Government, industry, and the scientific and medical
communities have a responsibility to educate the public and improve
the availability of unbiased information on genetically
modified crops and research activities.
Among the recommendations made by the Council are
the following:
With support from The Rockefeller Foundation, the Texas Advanced Technologies Program, and other sources, we have used physical (electroporation, microprojectile bombardment) techniques to transform rice cells or tissues and have developed reliable procedures for regenerating fertile rice plants. From examining genomic blot analysis of numerous gene constructs, we became concerned by the frequent insertion of multiple copies of the transgene and by the fact that many of these copies were found to be rearranged. Although early (callus-stage) screening of easily-detected resistance marker or reporter (e.g., GUS) genes can facilitate the recovery of plants expressing the gene of interest, we noted that primary and progeny plants not thus screened frequently failed to yield the expected expression of the transgene constructs, suggesting that silencing had occurred. Whereas important insight to gene silencing and cosuppression had been reported in dicot plants1, no such reports existed for monocots and we decided to undertake a detailed analysis of our transgenic rice lines.
In one set of experiments, we recovered a large number of rice transformants in which a CaMV 35S promoter was used to drive expression of a Bt cryIIIA coding region and the maize ubiquitin promoter (mubi) to drive the bar gene as a selectable marker for bialaphos herbicide resistance. Detailed analysis of these plants revealed that they contained multiple copies and rearranged inserts that frequently displayed non-Mendelian segregation of transgene expression.
Characterization of R1 progeny by methylation-sensitive isoschizomer restriction digestion, nuclear run-on, and RNase protection assays revealed that the 35S and mubi1 promoters were extensively methylated and transcriptionally inactivated in the silenced lines2,3. The silenced state was stably transmitted to the next generation as indicated by the lack of expression of the bar gene in R2 progeny derived from the silenced lines. The epigenetic modification of the transgene sequences was further confirmed by the reactivation of the bar gene expression in R2 seedlings (from the silenced lines) germinated on medium containing 5-azacytidine (5azaC). Analysis of progeny of selfed plants homozygous for herbicide resistance revealed that silencing can arise in later (R2 and R3) generations, resulting in bialaphos-sensitive plants that showed no bar transcripts.
As in the case of our rice lines, DNA methylation is frequently associated with transgene silencing4. However, in most instances, it is likely that silencing arises from heterochromatin formation resulting from the binding of proteins such as MeCP2 that recognize methylated DNA and that, in turn, recruit histone deacetylases to form a repressive chromatin architecture5. DNA methylation can be stimulated in many ways. Although cruciform integration intermediates appear to be especially well-recognized by DNA methyltransferases6, repeat sequences and perhaps certain features of sequence composition or structure of transgenes mark them as being invasive DNA. In accord with the concepts of Bestor and Tycko6, we suggest that several "genome intruder surveillance and modulation systems" (GISMOS) exist to screen, detect, and modify both extra- and intra-genomic DNA parasites such as transposons7. The evolution of sensitive systems for protecting self DNA from non-self DNA perhaps parallels that of the immune system and accounts for the ability of plants and other organisms to inactivate transgenes. Similar rationale exists for the development of post-transcriptional silencing systems that are very effective against viral invasion and aberrant RNA expression levels from transgenes (reviewed in 8).
Is it reasonable to believe that the design of transgenes can be such that they evade recognition by GISMOS? Like aircraft that escape radar detection, we can envision such designs as "stealth" constructs, and we have speculated that this may be feasible as we gain better insight to the full spectrum of silencing mechanisms7, 8. Powerful approaches are now being employed to increase such understanding, landmark discoveries such as finding in Arabidopsis that plants with a deficient methylation system (the ddm1 mutation) were unable to maintain silencing and that plants with mutation of the MOM gene release transcriptional silencing9. The fact that the ddm1 gene encodes a SWI2/SNF2-like protein10 reinforces the connection between chromatin architecture, methylation, and silencing, although full insight to these interactions remains to be uncovered. The directed debilitation of plant genes conjectured to be involved in gene silencing, for example by RNAi approaches11, promises to reveal the GISMOS' inner secrets. As the veils are removed, it appears certain that we will also obtain novel revelations concerning epigenetic regulation of plant development that will be helpful in developing stealth transgene strategies.
Sources
1. Matzke MA and Matzke AJM. 1990. Gene Interactions and Epigenetic Variation in Transgenic Plants. Developmental Genetics 11: 214-223.
2. Kumpatla SP and Hall TC. 1999. Organizational complexity of a rice transgene locus susceptible to methylation-based silencing. IUBMB Life 48: 459-467.
3. Kumpatla SP, Teng W, Buchholz WG, and Hall TC. 1997. Epigenetic transcriptional silencing and 5-azacytidine-mediated reactivation of a complex transgene in rice. Plant Physiology 115: 361-373.
4. Selker EU. 1999. Gene silencing: Repeats that count. Cell 97: 157-160.
5. Nan X, et al. 1998. Transcriptional repression by the methyl-CpG-binding protein MeCP2 involves a histone deacetylase complex. Nature 393: 386-389.
6. Bestor TH and Tycko B. 1996. Creation of genomic methylation patterns. Nature Genetics 12: 363-367.
7. Kumpatla SP, et al. 1998. Genome intruder scanning and modulation systems and transgene silencing. Trends in Plant Science 3: 97-104.
8. Iyer LM, et al. 2000. Transgene Silencing in Monocots. Plant Molecular Biology 43: 323-346.
9. Amedeo P, et al. 2000. Disruption of the plant gene MOM releases transcriptional silencing of methylated genes. Nature 405: 203-206.
10. Jeddeloh JA, Stokes TL, and Richards EJ. 1999. Maintenance of genomic methylation requires a SWI2/SNF2-like protein. Nature Genetics 22: 94-97.
11. Smith NA, et al. 2000. Total silencing by intron-spliced hairpin RNAs. Nature 407: 319-320.
Tim Hall
Institute of Developmental and Molecular Biology
Texas A&M University
tim@idmb.tamu.edu
FUNGICIDAL POTATOES Recent federal regulations banning the use of many
popular agricultural fungicides are leaving farmers with
fewer weapons to combat post-emergent fungal diseases
affecting crops. Various new strategies are being
developed ranging from protective spray-on emulsions to
rapidly biodegradable compounds that leave no harmful
residue. However, many of these techniques are not effective
for certain crops and soil-borne fungi.
Monsanto Company is using biotechnology to
develop several strategies to reduce fungal damage without
the need for fungicide applications. The laboratory of
Jihong Liang has recently produced a transgenic potato capable
of warding off the fungal pathogen Verticillium
dahliae. This potato was designed to express a naturally
occurring antimicrobial compound belonging to a group of
proteins called defensins1.
The fungus, Verticillium dahliae, lurks in the soil and
kills young plants, robbing farmers of yield. Potato growers
lose between $70 million and $140 million in profits to
the fungus every year. The fungus is usually kept in check
by fumigation of the soil. Fumigation kills both the
harmful pathogens and the beneficial microorganisms, so it is not
a particularly attractive option for the environment, nor
for most growers because of the cost and health hazards
from the chemicals.
Defensins are cysteine-rich peptides ranging in size
from 45 to 54 amino acids. Found in both animals and
plants, defensins are structurally related to lectins, scorpion
toxins, and other small toxic proteins containing a
beta-hairpin configuration with two adjacent disulfide bonds. A
variety of plants constitutively produce defensins in their seeds
and damage-induced defensin production is also noted in
many plants2. Defensins from barley
(Hordeum vulgare), horse chestnut (Aeculus
hippocastanum), j'oublie (Pentadiplandra
brazzeana), radish (Raphanus sativus), tobacco
(Nicotiana alata) and wheat (Triticum
turgidum) are well characterized and extensively studied.
Plant defensins are most effective at inhibiting the
growth of Gram-positive and Gram-negative bacteria and a
broad range of fungi. Cell culture studies indicate that
defensins have little toxicity to mammalian and plant cells,
though insect toxicity is possible, depending on the type of
defensin and variety of insect involved. Studies on cotton led to
the discovery of a defensin capable of killing mosquito
(Aedes camptorhynchus) larvae3.
Defensins inhibit mircrobial growth by interfering with
the action of signal-regulated protein kinases and
calcium-binding regulatory proteins such as calmodulin. They
act either as antagonists or as kinase substrates. The
effectiveness of defensins against particular target
organisms depends on the affinity of the defensins to host
protein kinases3.
Fungistatic defensins are divided into two groups.
One group interferes with hyphal growth causing
morphological abnormalities such as hyperbranching and swelling.
The other group inhibits fungal metabolism by
obstructing metabolic functions.
Liang's team tested the antifungal properties of
alfAFP, a gene for the defensin protein isolated from alfalfa
seeds (Medicago sativa), on the growth of
Verticillium dahliae and Phytophthora
infestans, both common pathogenic fungi of potatoes. The
alfAFP gene for the defensin was isolated from mature seeds using degenerate
oligionucleo-tide primers matching six amino acids in the
alfAFP sequence. AlfAFP cDNA was then generated and
combined with a 35S promoter from figwort mosaic virus.
This combination was cloned between the T-DNA borders
of pMON17227 configured to produce abundant
alfAFP expression. A glyphosate resistance gene was placed
after the promoter as a transformation marker. The
construct was introduced into "Russet Burbank" potato cells using
an Agrobacterium vector.
Greenhouse and field studies were performed on transgenic and control potatoes exposed to
Verticillium dahliae. "Russet Ranger" potatoes, which are
naturally resistant to Verticillium dahliae, were used as
positive controls. In both greenhouse and field trials, the
transgenic plants proved significantly more effective at
reducing Verticillium dahliae damage than control plants.
However, the transgenic plant's ability to fight off
other fungi proved ineffective. Defensins may have to be combined
with genes encoding additional defensive strategies, such
as enzyme inhibitors and cell wall disrupting compounds,
to produce plants with broad antimicrobial activity.
This investigation is one of several studies designed
to introduce antifungal properties into economically
important plants. For example, Japanese researchers at the
National Institute of Agrobiological Resources attained
similar success in inhibiting the growth of several bacteria
and fungi by expressing sarcotoxin IA in tobacco plants.
These and other studies indicate the possibility of producing a
GM potato that expresses a defensin against
Phytophthora infestans, also known as potato late blight.
Conventional chemical and cultivation strategies are not effective
at reducing potato late blight loss and often involve high
costs, toxic pesticides, or result in the production of
resistant strains of Phytophthora.
Potatoes are also subject to damage, spoilage, and
discoloration by a host of post-harvest fungi including
common fungi such as Aspergillus. Most of the damage
affecting the marketability of the potato occurs when the
fungi penetrate or degrade the skin or epidermis.
Potatoes capable of producing defensins against these pests
would prove valuable for potato producers.
The use of defensins in GM crops has raised food
safety concerns. One criticism cites the possibility of
allergic reactions occurring in animals and humans due to
large levels of defensins in their diets. However, there are
few clinical or field studies supporting this allegation. The
highly conservative nature of defensins has also lead to
speculation of its being biologically active in animal digestive tracts.
Critics have also suggested that the use of these
transgenic potatoes may result in the appearance of
defensin-resistant fungal mutants. However, Felix Althaus, veterinary
faculty at the University of Zurich, sees little probability of
this technology producing target organisms resistant to
the defensins. Althaus claims that millions of years of
evolution has not yet led to microorganisms resistant to
defensin attacks by regular hosts. This mostly likely is also true
for plant defensins that target bacteria, fungi, and insects
known to evolve resistant strains very rapidly.
Sources
1. Gao A-G, et al. 2000. Fungal pathogen protection in potato
by expression of a plant defensin peptide. Nature
Biotechnology 18(12): 1307-1310.
2. De Samblanx, et al. 1997. Mutational analysis of a
plant defensin from radish (Raphanus sativus
L.) reveals two adjacent sites important for antifungal activity.
Journal Biochemistry 271(2): 1171-1179.
3. Polya GM. 1999. 1998 Annual report of the
Asian-Australian Centre for the Study of Bioactive Medicinal Plants.
LaTrobe University, Australia.
Brian R. Shmaefsky
CROP SCIENTISTS REPORT RESEARCH HEADWAY ON FHB GRAIN DISEASE
Crop scientists are making progress in their efforts to
find ways of controlling Fusarium Head Blight (FHB) in
small grains. Over 175 crop scientists from around the world
and leaders of the US wheat and barley industry met in
Cincinnati recently in a national forum to discuss advancements
in the research of FHB, commonly called scab. The
fungal disease has plagued wheat and barley production in
many areas of the United States since the early 1990s,
resulting in farm losses in at least 18 states valued conservatively
at over $2 billion, according to university and industry
estimates.
Three years ago, the US Wheat and Barley Scab
Initiative convened to address FHB in wheat and barley. The
$4.3 million national research initiative in the 2000 federal
fiscal year involved 73 scientists working on 104 projects,
carried out in 23 states at 22 land grant universities and the
US Department of Agriculture's Agricultural Research
Service, which funds the Initiative. At the Cincinnati research
forum, scientists reported advancements in six distinct
program areas of the Initiative: Variety Development and
Uniform Nurseries; Epidemiology and Disease Management;
Food Safety, Toxicology, and Utilization; Chemical and
Biological Control; Germplasm Introduction and Evaluation;
and Biotechnology.
Jim Anderson, wheat breeder at the University of
Minnesota, said there is encouraging progress in the use of
DNA markers to help identify genes in wheat and barley
responsible for scab resistance. Molecular markers are
essentially an accurate means of "fingerprinting" germplasm,
enabling researchers to keep track of traits such as scab
resistance and, based on the pattern revealed by these markers,
to select crosses to make improved wheat and barley
varieties for better scab tolerance.
A full report of research conducted under the US Wheat
and Barley Scab Initiative and discussed at the Forum in
Cincinnati will be available in the 2000 National Fusarium
Head Blight Forum Proceedings accessible on the Internet at:
http://www.scabusa.org. The Proceedings include summaries of 26 research projects focusing on biotechnology.
Tracy Sayler
BIOTECH FEEDS UNDETECTABLE IN ANIMAL FOOD PRODUCTS
Today's biotech crops represent some of the first
products of modern biotechnology available for enhancing
environmental stewardship and eventually improving the
safety and nutritional value of food. These crops have
been available commercially in the US since 1995, and
today include crops such as corn, soybeans, cotton, sugar
beets, canola, and potatoes. Biotech plants include Bt corn and
Bt cotton that contain genes conferring pest resistance
derived from Bacillus thuringiensis, and Round-Up
Ready® Soybeans exhibiting tolerance to the herbicide glyphosate.
Currently available biotech crops can be effective
for controlling economically important pests while also
reducing use of chemical pesticides and herbicides. In
addition, workers have reported lower levels of fumonisin
mycotoxins in Bt corn1. Mycotoxins are probable carcinogens
and can cause liver damage in humans and livestock.
Recent discussions by the media have focused on
the safety of biotech crops for the human diet. In fact,
safety and efficacy are essential regulatory considerations
applied to biotech crops worldwide, and when concerns
exist, approval for use in the human food chain can be
denied. However, as a result of the unintended presence
of StarLink corn in some human food products (see
ISB News Report, October 2000
Human consumption represents a small percentage of
the total market for crops such as corn. Corn production in
the US accounts for nearly 80 million acres, with a
farmgate value nearing $40 billion dollars. However,
approximately 93% of US-grown corn is used for livestock feeds.
In addition, other crops such as soybeans provide a
significant proportion of livestock diets.
Safety reviews conducted by the US
Environmental Protection Agency, US Department of Agriculture,
US Food and Drug Administration, and other
international regulatory agencies have identified no risk to mammals
fed currently available biotech crops. More than 40
animal feeding studies, designed to detect any unintended
effects in livestock fed biotech crops, have been completed or
are currently in progress. Many of these studies, conducted
in Europe and the US, compared the performance of
livestock fed either biotech or non-biotech feeds and
have included dairy cows, beef cows and feeders,
broilers, layers, swine, sheep, and catfish. The biotech crops
studied were pest protected corn and herbicide resistant
soybeans, corn, and sugar beets. Conclusions for these studies
have been very consistent—no detrimental effects have
been found in livestock fed biotech crops.
Other studies have been conducted to determine
whether milk, meat, or eggs from livestock fed biotech crops
and their non-biotech counterparts can be differentiated.
To investigate milk composition and dairy cow health for
cows consuming Bt corn, a feeding study was designed
and conducted during 1996 in our facility at Iowa State
University (ISU). Transgenic Bt plants express
insecticidal proteins to protect against damage by European
Corn Borer and other lepidopteran pests while reducing the
need for chemical pesticides.
For this study, high-producing dairy cows were fed
diets containing whole plant green chop corn from one of
three sources: two different insect-protected hybrids (Bt
events 176 and Bt11) and one hybrid that was a
non-biotech genetic counterpart to one of the test
hybrids2. Whole plant green chop corn was used instead of silage because
previous work had indicated that the transgenic proteins in
event 176 Bt hybrids were degraded rapidly during the
ensiling process3. Thus, the ISU dairy study attempted to
maximize exposure of cows to dietary sources of Bt proteins.
Fresh green chop corn was harvested daily. Cows
were fed the test diets for a total of 14 days, during which
time milk and feed samples and cow performance and
health data were collected. Feed samples were evaluated
to confirm the presence of transgenic proteins in biotech
corn feed and the lack of transgenic proteins in diets of the
non-Bt corn group. Milk production, feed intake, udder
health, and milk composition (fat, protein, lactose, other
solids, etc.) were similar for cows fed all three
diets2.
The laboratory was unable to detect transgenic proteins
in milk samples collected from cows fed the three
study diets2. Based on current knowledge of protein digestion
and metabolism by dairy cows and other mammals, it
was anticipated that the transgenic proteins would not
be present in milk. To verify laboratory tests,
purified transgenic proteins were intentionally added to
duplicate milk samples and analyzed along with the original
samples in blind tests. In every case, the laboratory tests
detected transgenic proteins in the spiked samples, and were
unable to detect these proteins in the original `unspiked'
milk samples. The ISU dairy study further analyzed the
original milk samples to determine whether naturally occurring
and transgenic plant source DNA can be detected in
milk. Neither transgenic nor naturally occurring plant
source DNA was detected4. Our findings indicate that milk
from cows fed Bt and non-Bt corn cannot be differentiated.
Similar differentiation studies conducted in Europe and
the US have evaluated milk, meat, eggs, and other tissues
from dairy cattle, beef cattle, broilers, and layers fed biotech
and non-biotech crops. Two studies completed in
Europe reported finding small fragments of a naturally
occurring (non-transgenic) plant chloroplast gene in animal
tissues such as lymphocytes and
leucocytes4. However, in these same studies, no transgenic DNA was found. Results
from other studies indicated no plant source DNA
(naturally occurring and transgenic) was detected in meat, milk,
eggs, and other tissues such as spleen4. In addition, a dairy
cow feeding study using StarLink corn was unable to
find transgenic StarLink proteins in milk from cows in the
study5. Most importantly, results from all these studies agree on
two points: 1) no transgenic DNA and 2) no transgenic
proteins have been detected in meat, milk, and eggs.
Biotech crops hold great promise for the future of
animal agriculture by providing feedstuffs that are more
nutritious and healthful, have pharmaceutical or nutriceutical
value, and contain nutrients that improve the composition of
milk, meat, and eggs. Further, many are excited about
prospective biotech crops in which nutrients will be more
available, thus helping to reduce the environmental impact of
animal waste. Current studies corroborate the safety for
human and animal food supplies of fully approved biotech
crops. Further, these studies document that milk, meat, and
eggs from animals fed biotech and non-biotech crops cannot
be differentiated. Rigorous regulatory measures and
scientific studies tailored for specific biotech crops will continue
to improve the safety and wholesomeness of food supplies
in the US and worldwide.
Sources
1. Munkvold GP and Hellmich RL. 1999. Genetically
modified, insect resistant corn: Implications for disease
management. APSnet Plant Pathology On-Line.
http://www.scisoc.org/feature/BtCorn/Top.html.
2. Faust M and Miller L. 1997. Study finds no Bt in milk.
IC-478. Fall Special Livestock Edition, 6-7. Iowa State
University Extension: Ames, Iowa.
3. Fearing PL, et al. 1997. Quantitative analysis of
CryIA(b) expression in Bt maize plants, tissues, and silage and stability
of expression over successive generations. Molecular
Breeding 3:169.
4. Faust MA. 2000. Livestock products - composition
and detection of transgenic DNA/proteins. In Proceedings
of Agricultural Biotechnology in the Global
Marketplace. American Dairy Science Association: Savoy. IL.
5. Aventis. 2000. Livestock studies. Aventis Crop Science.
http://www.us.cropscience.aventis.com/AventisUS/CropScience
/stage/html/livestockstudies.htm
Marjorie A. Faust
INSECTICIDES TO TARGET INSECT LIFE CYCLE
[From Australia's Commonwealth Scientific and
Industrial Research Organisation (CSIRO) Press Release]
A new generation of chemical pesticides will disrupt
the life cycle of insects, preventing them from reaching
their normal adult form. The pesticides have been developed
by a team of scientists from CSIRO and the US who
have cloned two proteins that regulate the level of insect
juvenile hormone. According CSIRO, the pesticides attack
insect juvenile hormone, which has no equivalent in
higher animals, they will be harmless to vertebrate animals
and humans.
Two key proteins called juvenile hormone esterase
(JHE) and juvenile hormone binding protein (JHBP) control
the level of juvenile hormone. Juvenile hormone in turn
regulates the passage of juvenile insects through their
various moults to become adults. "The level of this hormone
is crucial in development where it controls the process
of metamorphosis," says Dr. Tony Zera of the University
of Nebraska. "In insects such as locusts, juvenile hormone
is also one of the factors that controls the switch
between their sedentary stage and their migratory stage, a
flight stage in their life cycle during which they are a
moving target and much harder to control."
"In many insects which have different adult forms
specialized for different functions, the hormone also
determines which of these adult forms they become," says Dr.
Zera. "Alterations to JHE and JHBP disrupt development and
in the case of insects like crickets and grasshoppers
can prevent commencement of the migratory phase.
The important step from the point of view of
commercial application has been the cloning of JHE and JHBP
in CSIRO Entomology's biotechnology program. This
means that we can now apply for patents for the use of
these genes in the search for new, safer chemical insecticides."
Dr. John Oakeshott, leader of CSIRO
Entomology's biotechnology program, says that his research team
has cloned the genes producing JHE and JHBP from
several different insects. "We can now format these proteins
in high speed screening systems to scan libraries of
natural and synthetic chemicals for molecules that would
disrupt the function of the proteins and give us new candidates
for chemical insecticides," he says.
For more information, contact:
ISB News Report
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Ruth Irwin, Editor (rirwin@nbiap.biochem.vt.edu)
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Information Systems for Biotechnology, 120 Engel Hall, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, tel: 540-231-2620, fax: 540-231-2614, email:
isb@vt.edu
Department of Biology and Environmental Sciences
Kingwood College
bshmaefs@nhmccd.edu
Journalist
Fargo, ND
tsayler@corpcomm.net
Department of Animal Science
Iowa State University
mafaust@iastate.edu
Dr. Tony Zera at azera1@unl.edu
Dr. John Oakeshott at j.oakeshott@ento.csiro.au
120 Engel Hall
Virginia Tech
Blacksburg, VA 24061
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