GENTECH archive 8.96-97

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                ISB News Report  - December 1996


IN THIS ISSUE

 Transgenic Cotton with Improved Polyester-like Fiber
 Herbicide-Resistant Crops Offer Hope in Fight Against
 Parasitic Weeds
 Transgenic Animals as Organ Donors
 Technology Acquisition: Agrevo Makes a Move
 Grant and Funding Information on the Internet


PLANT RESEARCH NEWS

TRANSGENIC COTTON WITH IMPROVED POLYESTER-LIKE FIBER
Cotton is the undisputed king among cash crops in many countries
such as India, Egypt and the U.S. While spectacular increases in
cotton yield have been achieved in the past decades through
conventional breeding, modification of fiber traits has remained
a challenging task. Both the textile industry and consumers would
benefit greatly from cotton fibers that are stronger, longer,
less water absorbent, resistant to wrinkling and shrinkage, and
which bind better to dyes. Even better would be fibers that
display naturally bright colors with no added dyes. A recent
report from Agracetus describes what may be the first yarn in
eventually weaving this scenario (1). The report describes the
development of transgenic cotton plants engineered with 
bacterial polyester genes and fiber-specific promoters, which
produce novel cotton fibers having a normal texture but with
thermal properties of a winter-weight fabric.

To develop the polyester-cotton, Dr. Maliyakal John and Dr. Greg
Keller of Agracetus employed phaB and phaC genes isolated from
the bacterium Alcaligenes eutrophus, which encode key enzymes
necessary for the production of the biodegradable thermoplastic
polyhydroxybutyrate (PHB). Earlier, Dr. John's research group
identified two genes from cotton fibers that are developmentally
regulated and tissue-specific in expression (2, 3). The gene E6
is expressed during early fiber development in elongating fibers
while FbL2A is expressed during late fiber development and is
associated with active secondary wall formation when cellulose
deposition occurs. John and Keller hooked these fiber-specific
promoters to the coding region of the phaB gene, while phaC was
placed under the control of a constitutive CaMV 35S promoter.
Nearly 14,000 cotton seeds were subjected to the electrical
discharge particle bombardment procedure to eventually produce
eight transgenic cotton plants. The cotton fibers isolated from
transgenic plants grown in the greenhouse appeared normal in
texture but when tested using epiflourescence and transmission
electron microscopy, the PHB could be clearly observed as
clusters of granules in transgenic fibers. The presence of these
plastic granules in fibers were further confirmed with high
pressure liquid chromatography and gas chromatography-mass
spectrometry.

Agracetus scientists then analyzed the cotton fibers for their
thermal properties and found that these transgenic fibers and the
fabric made from their yarn "conducted less heat, cooled down
slower and took up more heat than the conventional cotton fiber".
The new fibers had 12% higher heat uptake than the control fibers
and with noticeably lower thermal conductivity. Thus, the
transgenic cotton fiber with an introduced polyester gene had
insulation and warmth qualities reminiscent of acrylic,
suggesting potential applications in winter clothing.

Dr. John, a native of India who heads the Fiber Technology
Division at Agracetus, concedes that changes in the thermal
properties of transgenic fibers are still small and it is
necessary to achieve much higher expression of the PHB genes to
make an impact on fiber product applications. Nevertheless, this
research represents another new chapter in agricultural research
where the potential of biotechnology is being increasingly
harnessed to add value to farming and develop improved consumer
products. 

References
(1) M. E. John and G. Keller. 1996. Metabolic pathway engineering
in cotton: Biosynthesis of polyhydroxybutyrate in fiber cells.
Proc. Natl. Acad. Sci. USA. 93:12768-12773.

(2) M. E. John and L. J. Crow. 1992. Gene expression in cotton
(Gossypium hirsutum L.) fiber: Cloning of the mRNAs. Proc. Natl.
Acad. Sci. USA. 89:5769-5773.

(3) J. A. Rinehart, M. W. Petersen and M. E. John. 1996.
Tissue-specific and developmental regulation of cotton gene
FbL2A: Demonstration of promoter activity in transgenic plants.
Plant Physiol. 112: 1331-1341.

C. S. Prakash
Center for Plant Biotechnology Research
Tuskegee University
pakash@acd.tusk.edu 


HERBICIDE-RESISTANT CROPS OFFER HOPE IN FIGHT AGAINST PARASITIC
WEEDS
The advent of genetically engineered herbicide resistant crops is
a promising development in agriculture that will expand the range
of herbicides available for weed control in major field crops.
While this technology will supplement the current alternatives
for control of conventional weeds, it holds the potential to
finally give farmers the upper hand in the struggle against
parasitic weeds.

Parasitic weeds are flowering plants that have adapted a
specialized life style whereby they make a physical attachment to
another plant and then live either partially or wholly off the
resources produced by that host plant. This adaptation has
occurred in many plant families --- parasitic plants are not
uncommon, though we rarely notice them because they tend to be
small and live inconspicuously on their hosts. Perhaps the two
most familiar types in the U.S. are the mistletoes, which
parasitize tree branches, and the dodders, which grow in twiney
shoots that parasitize stems of many plant species. However, two
types of root parasites, the witchweeds and broomrapes, cause
destruction and crop loss throughout Africa, the Middle East,
Southern Europe, and wherever else in the world they have
established infestations.  

These parasites are among the most difficult weeds to control
because of their close association with the crop host plant. They
grow attached to the host root and don't produce an above-ground
structure until they are nearly ready to flower. By this time,
they have often caused significant damage by stealing much of the
water and photosynthates the host needs for its own growth. In
this way they do not present an accessible target for mechanical
weed control or direct spraying of herbicides. Generally, the
herbicides available that will kill the parasite will also
destroy the host crop, so farmers are limited to either the
costly and dangerous chore of killing the parasite seeds by soil
fumigation, or to giving up and planting alternative crops that
are not hosts for the parasites.  

Thus, it was a significant breakthrough when Israeli scientist
Danny Joel and colleagues reported that crops engineered for
herbicide resistance were able to withstand herbicide treatment
while the parasite plants were killed (1). They showed that
canola resistant to glyphosate was freed of broomrape parasitism
following glyphosate treatment. The glyphosate molecule is
readily translocated in plants, so after application to the host
foliage, it is taken into the translocation stream and dispersed
throughout the plant. Since the broomrape parasite taps into the
hosts phloem to obtain its food, in effect it was made to drink
the glyphosate along with its dinner. This principle worked
equally well for chlorsulfuron- and asulam-resistant tobacco
plants.

However, the mechanism of herbicide resistance was very
important. The plants engineered for resistance to glyphosate,
chlorsulfuron, and asulam were resistant because changes had been
made to the enzymes that would normally be inhibited by these
herbicides. In contrast, tomato plants that had been made
resistant to glufosinate by addition of an enzyme capable of
metabolizing the herbicide were just as susceptible to broomrape
attack following glufosinate treatment as were untreated control
plants. In this case the host plant avoided injury to itself by
degrading the glufosinate, but the result was that the herbicide
was rendered nontoxic before it reached the parasite.  

In order for this strategy to be used in controlling parasitic
weeds it will be necessary to engineer herbicide resistance into
the appropriate host crops. For broomrape this would require
creating resistant lines of sunflower, broad bean, and a range of
vegetable crops including (but not limited to) tomato, potato,
cabbage, cucumber, parsley and carrot. These are relatively low
acreage crops, so industry may be reluctant to commit the labor
and  expense, and deal with potential risks, in order to
transform all host crops. For the witchweeds, which primarily
attack cereals (corn, sorghum, and millet), this should not pose
such a problem.

Indeed, a corn hybrid with resistance to the herbicides imazapyr
and imazethapyr is commercially available and was recently used
by G. Abayo and coworkers in Kenya to test the ability of these
herbicides to control witchweed (2). Their approach was unusual,
however, in that rather than apply the herbicides as a foliar
spray, they added one ml of herbicide solution along with each
seed in the planting hole. The imazapyr treatment reduced the
number of emerged witchweed plants per plot by over 90% at 8
weeks and 50% at 12 weeks after planting, and greatly reduced
seed production by those parasites that did emerge. This resulted
in a tripling of crop yield relative to untreated plants.  

Although the mechanism of how this treatment works has not been
proven, it is most likely due to the herbicide being taken into
the seed or germinating seedling and transferred to the parasite
as described above. The effect is almost like a temporary
vaccination for the crop, with a small amount of herbicide
absorbed into, and circulating through the young developing
plant, providing protection against any parasite that makes a
vascular connection with the host. Because witchweed growing on a
young host causes more damage than those growing on an older
host, this delay of parasitization on the corn plants can greatly
increase yields.  

It is a cruel irony that the people who must face the most severe
challenge in controlling parasitic weeds are some of the world's
poorest subsistence farmers. The beauty of a novel technique such
as applying an herbicide dose directly with corn seed is that the
farmer need not buy expensive herbicide spraying equipment nor be
skilled in its use. In this case, creative herbicide application
combined with biotechnology can offer hope in alleviating crop
devastation caused by these unique plants.

References

1)  Joel, D., Y. Kleifeld, D. Losner-Goshen, G. Herzlinger, and
J. Gressel.  1995.  Nature 374:220-221.

2)  Abayo, G.O., J.K. Ransom, J. Gressel, and G.D. Odhiambo. 
1996.  pp. 761-768 in: M.T. Moreno, J.L. Cubero, D. Berner, D.M.
Joel, L.J. Musselman, and C. Parker (eds.).  Advances in
Parasitic Plant Research, Cordoba, Spain.

Jim Westwood
International Research and Development
Virginia Tech
westwood@vt.edu


ANIMAL RESEARCH NEWS

TRANSGENIC ANIMALS AS ORGAN DONORS
Advances in medical science have made many organ transplants,
such as heart, kidney, and liver, almost routine procedures.
However, the chronic shortage of suitable organs for
transplantation limits the number of these life-saving
operations. Of the estimated 60,000 people annually that need an
organ transplant, only half actually receive a transplant. In the
U.S. alone, approximately 3,000 people die each year waiting for
a transplant.

Increasing public awareness about the importance of organ
donation has not effectively increased the supply of organs to
meet the demand. As an alternative approach, xenotransplantation
or the transfer of organs between species has been proposed as a
possible solution to alleviating the shortage of transplantable
organs. As with any organ transplant, whether it be human-human
or animal-human, the major medical obstacle that must be overcome
is hyperacute rejection of the transplant by the host immune
system. The complement system, which is a series of proteins that
provides first line defense against foreign organisms or tissues,
initiates a cascade of events that leads to the destruction of
the foreign material in a matter of minutes. The presence of
complement masking or shield proteins prevents the complement
system from attacking a person's own cells. To prevent rejection
of animal organs in humans, researchers are developing transgenic
animals that express human shield proteins on the surface of
their organs. These genetically modified organs should in theory
escape the destructive effects of the complement system when
transplanted into a human.

Imutran (Cambridge, U.K.) and DNX (Princeton, NJ) are two of the
leading companies developing transgenic animals as organ donors.
Pigs are the favored model for these transgenic studies because
the size, anatomy and physiology of pig organs are compatible
with humans. Also, there are very few swine diseases that can be
transmitted to humans. Imutran has successfully produced
transgenic pigs that express the human shield protein, decay
accelerating factor (DAF). Transfer of DAF-expressing pig hearts
into monkeys under severe immunosuppression showed an increase in
survival time of the transplant. DNX has also produced transgenic
pigs expressing shield proteins and likewise has demonstrated a
delay in the onset of hyperacute rejection of the genetically
modified organ. Although these results show promise in mitigating
hyperacute rejection by the complement system, further technical
obstacles need to be overcome. For example, the xenograft must
still survive later attack from other components of the immune
system.

This research raises a number of scientific and ethical
considerations. Should transgenic animals be created as a source
of organs?  Proponents claim that harvesting an animal for its
organs is not any different than the current practice of
harvesting animal tissues for food. Because a pig's lifespan is
shorter than a human's, would a pig organ be genetically
programmed to senesce sooner than the human body in which it was
transplanted? Would the public accept animal organs for
transplantation? In a survey of attitudes of Australian nurses
towards organ donation, two thirds were opposed to the use of
animal organs for transplant. So although successful
xenotransplantation may represent a breakthrough for medical
science, the procedure will be of limited value if people are
unwilling to accept animal organs.

Eric A. Wong
Department of Animal and Poultry Sciences 
Virginia Tech
ewong@vt.edu


INDUSTRY NEWS

TECHNOLOGY ACQUISITION: AGREVO MAKES A MOVE
In a recent article, I described Monsanto's growing emphasis on
biotechnology as a key piece of its agricultural arsenal,
bolstered by the apparent success of recently launched products
including recombinant soybean. As agricultural biotechnology
continues to reveal its commercial value, other multinational
agrochemical companies are aggressively investing in
biotechnology as a  future cornerstone of their business. An
article in a recent issue of Nature Biotechnology (1) describes
the acquisition of PGS International (Amsterdam, the Netherlands)
by the European agri-chemical company AgrEvo. Not only does this
acquisition point to the continued consolidation of the
agrochemical and plant biotechnology sectors, but also the
growing value that companies are placing on innovative,
patent-protected, plant biotechnologies. The PGS/AgrEvo deal was
valued at $730 million, representing one of the largest ever
acquisitions of a privately owned biotechnology company. Over 95
percent of the purchase price represents AgrEvo's valuation of
technology, as PGS's assets were worth only about $30 million. A
failed 1994 attempt by PGS to go public on NASDAQ would have only
valued the company at between $200-$250 million, well below
AgrEvo's price.

The Nature article points to PGS's position in the Bacillus
thuringiensis (Bt)-related insect resistant plant arena as a
major attractant of PGS. AgrEvo is hoping that access to PGS
patents and technology related to Bt will help it gain upwards of
15 percent market share of an estimated $6 billion global market
for genetically modified plants by the year 2005. AgrEvo inherits
PGS's current patent infringement suites against Ciba Seeds and
Mycogen Plant Science related to Bt.

The significant price that AgrEvo was willing to pay for PGS
opens the door for other plant biotechnology firms to shop their
technologies, as some have started to do including European firm
Mogen. Demonstrated commercial success of plant biotechnology
products will also continue to enhance the value of firms working
in agbiotech, and likely increase the cash flowing into the
sector as investors recognize the opportunities for ample returns
on investment.

References

1.  Ward, M.  PGS-AgrEvo deal stirs up plant biotechnology.
Nature Biotechnology, Vol. 14, No. 10, October 1996, p. 1210

William O. Bullock
Institute for Biotechnology Information
http://www.biotechinfo.com


NET NEWS

GRANT AND FUNDING INFORMATION ON THE INTERNET
Agricultural biotechnology research in U.S. academic institutions
is supported largely by federal funding. However, it takes
considerable time and resourcefulness to keep track of the
multitude of grant opportunities that arise, often with short
notice. Now, there is help on-line for scientists: a free email
service called 'FEDIX Opportunity Alert' provides scientists with
periodic and customized information on research and education
funding programs from the twelve participating U.S. federal
agencies. To subscribe to this service, visit
<http://web.fie.com/> and choose 'FEDIX Opportunity Alert'.  You
will be asked to provide key words that describes your personal
interest profile.

The FEDIX conducts a daily search of grant announcements and
automatically emails you with any 'hits' that match your profile.
One could also conduct a search on the FEDIX web site for current
grant announcements from the participating agencies or browse by
'agency' or 'subject'. The FEDIX also provides links to the web
sites of many federal agencies including the USDA/CSREES
(http://www.reeusda.gov/). The National Science Foundation does
not participate in the FEDIX program, but you can visit the NSF
site at <http://www.nsf.gov/> and click on the 'Program Areas' to
learn about their grant programs.

C. S. Prakash
Center for Plant Biotechnology Research
Tuskegee University
prakash@acd.tusk.edu


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Editor.

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