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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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