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2-Plants: Pink Bollworms Could Adapt to Biotech Cotton



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                                  PART I
-------------------------------- GENET-news --------------------------------

TITLE:  Pink Bollworms Could Adapt to Biotech Cotton
SOURCE: Environmental News Service
        http://ens-news.com/ens/apr2003/2003-04-21-09.asp#anchor8
DATE:   Apr 21, 2003

------------------ archive: http://www.gene.ch/genet.html ------------------


Pink Bollworms Could Adapt to Biotech Cotton

TUCSON, Arizona, April 21, 2003 (ENS) - Researchers have found the pink
bollworm has three genetic mutations that confer resistance to genetically
modified, or biotech, cotton. According to a new report from a team of scientists
with the University of Arizona, the breakthrough could allow DNA based screens
that could be some 1,000 times more efficient in detecting pest resistance
than current measures. Normal pink bollworm caterpillars die when they eat the
bolls of genetically modified cotton plants that produce Bt (Bacillus
thuringiensis) toxin. Still, there are some resistant caterpillars that survive and
the researchers say it may only be a matter of time before the pink bollworm
and other pests adapt to Bt cotton. The study is published in the online
edition of the Proceedings of the National Academy of Sciences. They found that
each of the three mutations in pink bollworm occurs in a gene encoding a
protein called cadherin, which is what Bt toxins attack in insects. The research
team reports that each of the three resistance mutations disrupts
instructions for producing cadherin, thus blocking toxicity of Bt. This resistance is
inherited as a recessive trait, so caterpillars with two mutant versions of the
cadherin gene are resistant, but those with one or none are susceptible.
According to the study's author, the discovery will speed development of fast
and precise DNA-based tests for resistance, which can detect individuals with
single copies of resistance genes, and work with either live or dead insects.
And better knowledge of the genetic basis of resistance could open new
avenues for designing novel toxins to overcome the insects' defenses, the
researchers report.


                                  PART II
-------------------------------- GENET-news --------------------------------

TITLE:  Pest Resistance to Genetically Modified Crops Decoded
SOURCE: University of Arizona, USA, Press Release, by Susan McGinley
        
http://uanews.opi.arizona.edu/cgi-bin/WebObjects/UANews.woa/1/wa/CALSArticle?ArticleID=7200&wosid=34EECaD4cSurWMwXleLtL0
DATE:   Apr 16, 2003

------------------ archive: http://www.gene.ch/genet.html ------------------


Pest Resistance to Genetically Modified Crops Decoded

A team of scientists centered at the University of Arizona has discovered
that field populations of pink bollworm, the longtime scourge of Arizona
farmers, harbor three genetic mutations that confer resistance to genetically
modified cotton. This breakthrough paves the way for DNA-based screens that could
be 1,000 times more efficient in detecting pest resistance than the bioassays
that are currently used. The report appears in the online edition of the
Proceedings of the National Academy of Sciences (see sidebar).

Normal pink bollworm caterpillars die when they eat the bolls of genetically
modified cotton plants that produce Bt (Bacillus thuringiensis) toxin, but
resistant caterpillars survive. So far in cotton fields, resistance remains
rare in pink bollworm and other targeted insects. This enables Bt cotton to
control some major pests and has helped farmers reduce insecticide applications.

But it may only be a matter of time before the pink bollworm and other pests
adapt to Bt cotton. Already, more than 500 species of insects have evolved
resistance after repeated exposure to natural and synthetic toxins. Pest
populations also harbor rare genes that confer resistance to Bt. Scientists are
trying to delay pest resistance to Bt crops, but progress has been stymied by
lack of information about the genetic basis of such resistance. 

An international research team, led by Shai Morin in the UA College of
Agriculture and Life Sciences, found that each of the three mutations in pink
bollworm occurs in a gene encoding a protein called cadherin. In people and other
mammals, cadherins mediate cell-cell interactions and cancer may result if
they do not function properly. 

Harmless to people and animals, Bt toxins attack cadherin in gut membranes
of insects. The Morin team reports that each of the three resistance mutations
disrupts instructions for producing cadherin, thus blocking toxicity of Bt.

This resistance is inherited as a recessive trait, so caterpillars with two
mutant versions of the cadherin gene are resistant, but those with one or
none are susceptible. Together with previous evidence, the new results imply
that mutations in the cadherin gene may be central in pest resistance to Bt
crops.

This discovery will speed development of fast and precise DNA-based tests
for resistance. Unlike bioassays, DNA-based screening can detect individuals
with single copies of resistance genes, and work with either live or dead
insects. Knowledge of the genetic basis of resistance also opens new avenues for
designing novel toxins to overcome the insects' defenses.

SIDEBAR: Mutations in a key insect pest confer resistance to genetically
modified cotton, according to article #1036 of the April 29 issue of the
Proceedings of the National Academy of Sciences, online now in the Early Edition.


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