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[SANET-MG] mini chromosomes for better or for worse?
The ultimate in gene stacking is beginning to appear. Mini chromosomes
seem to be based on the B chromosomes which differ from A chromosomes
which are the normal well behaved chromosomes. Multiple B chromosomes
can be added to corn cells without much effect on the phenotype of the
corn. An article and an abstract describe the new technology.
New Gene Technology May Improve Corn Traits
- Wisconsin Ag Connection, May 25, 2007
http://www.wisconsinagconnection.com/story-national.php?Id=1207&yr=2007
It took nearly 20 years for researchers to develop the first commercial
genetically enhanced corn hybrids. The next generation of genetic
technology may be developed in less than half that time.
"Mini-chromosome stacking" uses the plant's DNA to simultaneously
introduce multiple genetic traits into plants, reducing the time and
cost required to develop and launch new products. The technology has
several advantages over current genetic technology, says Nathan Fields,
the National Corn Growers Association director of Research and Business
Development.
"There's no interference with the plant's native genome, so the new
traits can be delivered more precisely, with increased ability to
regulate trait expression," explains Fields. "Also, the technique makes
it easier to identify a genetically modified trait."
The mini-chromosome technology was developed at the University of
Chicago. Chromatin is the exclusive licensee. Earlier this year, it was
awarded a patent granting it exclusive rights for the mini-chromosome
technology in plants. NCGA has been working with Chromatin to help
develop the technology for agriculture and made an investment in the
company in 2004.
This week Monsanto signed a non-exclusive agreement to use the
technology in corn and other crops. Monsanto and Chromatin will conduct
a three-year program to complete development of the technology.
Chromatin estimates that mini-chromosome technology could accelerate the
timeline from research to commercial introduction for plants modified
with a single trait by two to three years (25 percent to 40 percent).
a related report:www.pnas.orgcgidoi10.1073pnas.0700932104
Construction and behavior of engineered
minichromosomes in maize
Weichang Yu, Fangpu Han, Zhi Gao, Juan M. Vega*, and James A. Birchler†
Division of Biological Sciences, 117 Tucker Hall, University of
Missouri, Columbia, MO 65211
Edited by Susan R. Wessler, University of Georgia, Athens, GA, and
approved April 12, 200
Engineered minichromosomes were constructed in maize by modifying
natural A and supernumerary B chromosomes. By using
telomere-mediated chromosomal truncation, it was demonstrated
that such an approach is feasible for the generation of minichromosomes
of normal A chromosomes by selection of spontaneous
polyploid events that compensate for the deficiencies produced. B
chromosomes are readily fractionated by biolistic transformation
of truncating plasmids. Foreign genes were faithfully expressed
from integrations into normal B chromosomes and from truncated
miniB chromosomes. Site-specific recombination between the terminal
transgene on a miniA chromosome and a terminal site on a
normal chromosome was demonstrated. It was also found that the
miniA chromosome did not pair with its progenitor chromosomes
during meiosis, indicating a useful property for such constructs.
The miniB chromosomes are faithfully transmitted from one generation
to the next but can be changed in dosage in the presence
of normal B chromosomes. This approach for construction of
engineered chromosomes can be easily extended to other plant
species because it does not rely on cloned centromere sequences,
which are species-specific. These platforms will provide avenues
for studies on plant chromosome structure and function and for
future developments in biotechnology and agriculture.
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