New Brunswick/Piscataway, New
Jersey
October 3, 2006
Genome Research’s cover story for Oct. 2 tells a tale of
“genome archaeology” by genetic researchers who dug deeply into
the long history of maize and rice. Their resulting insights
into plant genomic evolution may well fuel the fires of the
genetically modified organism (GMO) controversy.
“Our findings elucidate an active evolutionary process in which
nature inserts genes much like modern biotechnologists do. Now
we must reassess the allegations that biotechnologists perform
‘unnatural acts,’ thereby creating ‘Frankenfoods,’” said
Professor Joachim Messing, project leader and director of the
Waksman Institute of Microbiology at
Rutgers, The State University
of New Jersey.
By comparing corresponding segments of two maize (corn)
chromosomes with each other, and then to a corresponding segment
of rice, project scientists reconstructed a genetic history
replete with “reconfiguration and reshuffling, reminiscent of
working with Lego blocks,” Messing said.
Public awareness groups have argued that genetic engineering of
crops deviates from “natural processes” when biotechnologists
insert genes at seemingly random places, altering the normal
order of genes in the genome. The view of genes being fixed in
their position in the genome is largely based on studies in
animal genomes. In contrast to those studies, however, the
authors show that plant genomes evolved from a far more dynamic
structure than previously believed.
Maize dominates domestic agriculture, where approximately 9
billion bushels are produced annually at a value of $30 billion.
Corn is an important dietary staple in much of the third world
and a bio-fuel source; rice is the primary dietary staple for
more than half the world’s population.
Scientists have long known that the number of chromosomes among
some plant species has changed over time, with some evolutionary
phases showing four, six, eight or more sets. “Maize, for
example, began with four sets of chromosomes about five million
years ago and eventually trimmed down to the set of two that we
see today,” Messing said.
With these duplications and reductions, genes in chromosome
segments can be lost, replicated or shifted over to other
chromosomes, Messing explained. As a consequence, plant genomes
today contain rearranged segments and many duplicated regions
with corresponding sets of genes. In the maize genome, genes
were apparently lost in some parts and new “stuffer” pieces
(intervals between genes) inserted so that the corresponding
segments became different in size.
The researchers found that about 10 percent of the genes in the
maize segments were missing completely in rice, and about 20
percent were in new positions. Within the maize segments, genes
appear to be very mobile: 20 to 25 percent have “jumped” to
other locations in the genome during the course of evolution.
Two-thirds of the original genes from the ancestral four sets of
chromosomes have disappeared completely. Corresponding genes
wound up in completely different locations within the genome and
have likely undergone changes in how they affect biological
operations.
“The research, conducted by an international collaboration of
scientists, will help scientists and farmers improve these
significant crops and gain new and important insights in the
evolution of the grass species in general,” Messing said.
This undertaking included teams from the University of Arizona,
University of Georgia, Donald Danforth Plant Science Center in
St. Louis, The Institute for Genomic Research, the Broad
Institute at MIT and Harvard, Institute of Bioinformatics at the
GSF-Center for Environment and Health in Germany, and the Plant
Genome Initiative at Rutgers.
“The vast pool of genetic material in plants can be an important
resource from which biotechnology can draw genes for insertion
into an array of plants, generating unique genomes not
achievable by conventional breeding,” Messing said. “We could
engineer plants to provide a more sustainable, healthy and
productive source of food, while reducing the environmental
impacts of their cultivation.” |