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A team of scientists at the University of Missouri-Columbia has discovered a
way to create engineered mini-chromosomes in maize and attach genes to those
mini-chromosomes. This discovery opens new possibilities for the development
of crops that are multiply resistant to viruses, insects, fungi, bacteria
and herbicides, and for the development of proteins and metabolites that can
be used to treat human illnesses.
In a paper published in the Proceedings of the National Academy of Sciences
(PNAS), Weichang Yu, Fangpu Han, Zhi Gao, Juan M. Vega and James A. Birchler
built on a previous MU discovery about the creation of mini-chromosomes to
demonstrate that genes could be stacked on the mini-chromosomes.

"This has been sought for a long time in the plant world, and it should open
many new avenues. If we can do this in plants, many advances could be done
in agriculture that would not otherwise be possible, from improved crops to
inexpensive pharmaceutical production to other applications in
biotechnology," said Birchler, professor of biological sciences in the MU
College of Arts and Science.

A mini-chromosome is an extremely small version of a chromosome, the
threadlike linear strand of DNA and associated proteins that carry genes and
functions in the transmission of hereditary information. Whereas a
chromosome is made of both centromeres and telomeres with much intervening
DNA, a mini-chromosome contains only centromeres and telomeres, the end
section of a chromosome, with little else. However, mini-chromosomes have
the ability to accept the addition of new genes in subsequent experiments.

Birchler said there have been unsuccessful efforts to create artificial
chromosomes in plants but this is the first time engineered mini-chromosomes
have been made. Mini-chromosomes are able to function in many of the same
ways as chromosomes but allow for genes to be stacked on them. Although
other forms of genetic modification in plants are currently utilized, the
new mini-chromosomes are particularly useful because they allow scientists
to add numerous genes onto one mini-chromosome and manipulate those genes
easily because they are all in one place, Birchler said. Genetic
modification with traditional methods is more complicated because scientists
have little control over where the genes are located in the chromosomes and
cannot stack multiple genes on a separate chromosome independent of the
others.

By stacking genes on mini-chromosomes, scientists could create crops that
have multiple beneficial traits, such as resistance to drought, certain
viruses and insects, or other stresses. In addition, mini-chromosomes could
be used for the inexpensive production of multiple foreign proteins and
metabolites useful for medical purposes. Because of their protein-rich
composition, a part of the maize kernels (called an endosperm) can be used
to grow animal proteins and human antibodies that treat diseases and disease
symptoms. Mini-chromosomes could enable new and better production of these
foreign proteins and antibodies. In addition, scientists also may be able to
use them to develop plants better suited for biofuel production.

"The technique used to create our engineered mini-chromosomes should be
transferable to other plant species," Birchler said.

He said he hopes that he and other scientists can use the technique to
create mini-chromosomes in other plant varieties and produce more resistant
plant strains, develop more medically useful proteins and metabolites, and
study how chromosomes function.

Note: This story has been adapted from a news release issued by University
of Missouri-Columbia.

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