In doing so, the group, led by Jiming Jiang, a professor of horticulture at the University of Wisconsin-Madison, and C. Robin Buell of the Institute for Genomic Research in Rockville, Md., has exposed a supposedly barren region of a rice chromosome known as the centromere. The work, published in the current (Jan. 11) online editions of the journal Nature Genetics, reveals for the first time that a native centromere, typically composed of enormous spans of indecipherable, non-coding DNA, contains active genes.
The feat promises to help fill in a key genetic void and enhance the scientific understanding of chromosomes, the molecular structures that are found in all animal and plant cells, and are the essential carriers of hereditary information, enabling the processes of cell division and replication.
At a practical level, the work is a necessary step toward science's long-term goal of creating an artificial chromosome for plants, says Jiang. Such a tool, now available only for humans and yeast, would be an invaluable aid to scientific study and a precursor to precision plant engineering techniques.
"This is a significant step," says Jiang. "This is the first centromere to be sequenced at this level for any higher organism."
The centromere of rice, says Jiang, lent itself to sequencing because, unlike centromeres from other organisms, it is of a manageable size. Most centromeres are composed of vast stretches of what was once called "junk DNA," seemingly nonsense genetic sequences with no apparent coding function.
"They're humongous," Jiang explains. The DNA within centromeres is "highly repetitive, and it is resistant to mapping, cloning and sequencing," he says.