Tuesday, November 14, 2006

Writer: Philip Lee Williams, 706/542-8501, phil@franklin.uga.edu
Contact: Susan Wessler, 706/542-1870, sue@plantbio.uga.edu

UGA plant biologist edits research section on transposable elements in current issue of Proceedings of the National Academy of Sciences

Athens, Ga. – University of Georgia scientists are front and center in a special feature on genes published in the current issue of The Proceedings of the National Academy of Sciences (PNAS). The section, edited by Susan Wessler, Regents Professor of Plant Biology at UGA, includes eight invited and reviewed papers, including one from Wessler’s lab and another from the lab of Jeffrey Bennetzen, Norman and Doris Giles Professor and Georgia Research Alliance Eminent Scholar in the department of genetics at UGA.

The section comes on the heels of an announcement that the National Science Foundation has awarded a grant of $4.1 million to UGA to identify all the transposable elements (TEs) in maize and to generate an annotated database that will assist all future research in this crop plant crucial across the globe.

Transposable elements, popularly called “jumping genes,” are sequences of DNA that can move around chromosomes in a cell. At first thought to be molecular “junk,” they are now recognized as important, even crucial parts of the blueprints of plants and animals.

“When TEs were discovered in maize over 50 years ago, they were regarded as a curiosity,” Wessler (far right with her research associates Guojon Yang, left, and Eunyoung Cho, center) writes in her introduction to the special PNAS section. “Now they are known to be the most abundant component of probably all eukaryotic genomes. They account for almost 50 percent of the human genome and over 70 percent of some grass species, including maize.” (Eukaryotes are organisms, such as plants, animals or fungi, whose cells have a nucleus surrounded by a membrane.)

Because of their pervasive nature, TEs make up the vast majority of genome-sequencing projects, and the eight papers in the special section of PNAS address various aspects of current research on these “jumping genes.”

“We have known for many years that plants are much more variable in DNA content than is found in the animal kingdom,” said Bennetzen (below0. “For instance, dogs and humans contain about the same amount of DNA, although the genes differ in sequence quite a bit, but bread wheat contains almost 40 times more DNA than rice, and this degree of variation is not unusual for plants.” 

The article from the Bennetzen lab describes the use of transposable elements to measure the natures and rates of DNA sequence change in flowering plants. Their results indicate that flowering plants like wheat, barley and lotus are highly unstable, and use several different processes that change, delete or add DNA sequences. 

“The activities of these processes, including transposable element movement and amplification, are unique to each species, thereby creating the very different chromosomal compositions and structures seen in plants,” said Bennetzen.

In addition to editing and introducing the PNAS section, Wessler, along with colleagues in her lab, contributed a paper on transposable elements in rice. Despite the presence of TEs in the genomes of higher eukaryotes, the way these genes are amplified to large numbers without killing their hosts has remained largely unknown. Wessler’s lab reported how four strains of rice managed to amplify their TEs without harming the plants themselves.

Why are transposable elements so successful?  Some in the past thought they were simply “junk” that, much like viruses, can make lots of copies but do little to help the host. There is mounting evidence, however, that TEs help organisms evolve by making it easier to generate the sort of genetic novelty that is necessary for them to cope with a changing world.

Wessler is on the editorial board of PNAS, one of the world's most-cited multidisciplinary scientific journals. Since its establishment in 1914, it continues to publish cutting-edge research reports, commentaries, reviews, perspectives, colloquium papers and actions of the National Academy of Sciences, of which Wessler and Bennetzen are both members. Coverage in PNAS spans the biological, physical and social sciences.

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