WEST LAFAYETTE, Ind. -- Scientists have long known that genes make up only a tiny percent of the genetic material in a cell, but the question remained, "What are all those other things?"
A Purdue University study of the corn plant is fielding this question and producing some surprising kernels of knowledge about the organization and makeup of genetic material in plants. The findings offer new insights into why some plants have larger genomes than others, and they indicate that some plants may be able to thwart certain viruses that are devastating to humans.
Every living organism has a genome, the DNA in each cell's nucleus, which includes the active genes that determine the organism's characteristics. However, the genome also contains inactive pieces of DNA and other materials, many of which had not been identified.
In the Nov. 1 issue of the journal Science, Purdue biologist Jeffrey Bennetzen reports that the maize genome consists primarily of a class of mobile DNA called retrotransposons. Though these segments of DNA are not part of the active genes in the corn plant, they have the ability to multiply, move about and insert themselves throughout the genome.
"We knew that this mobile DNA was present to some extent in all genomes, including humans, but we didn't realize it could make up such a huge part of it," Bennetzen says. "Our study indicates that, in maize, mobile DNA accounts for more than 60 percent of the genome, which is two to three times more than what we would have expected to find."
Though scientists don't know how or why such segments of DNA accumulate in the genome, the fragments are thought to be generally harmless, Bennetzen says.
In the study, Bennetzen's group analyzed a region of the maize genome that contained
two genes. The group discovered 10 different classes of retrotransposons within the
region, with each class having 10 to 30,000 copies of its DNA segments scattered
throughout the rest of the genom
Contact: Susan Gaidos