Natural Selection of Gene Function Drives Retrotransposon Evolution in Rice

Transposons are small stretches of DNA that can move around to different positions in the genome of a single cell, and in the process dramatically increasing a genome's size. For years, researchers thought that most of this DNA was passive "junk" and knew little about it. New findings, however, are peeling back the odd and baffling world of transposons. Scientists at the University of Georgia found that natural selection on gene function is driving the evolution of one kind of transposable element called the LTR retrotransposon (LTR-R). LTR-R are a subclass of transposons particularly abundant in plants that replicate by reverse transcription (using an RNA intermediate in replication).

The researchers analyzed the patterns of genetic variation among LTR-R in rice “to investigate the type of selective forces that potentially limit their amplification and subsequent population of a nuclear genome.” They found that LTR-R are under significant evolutionary constraint, by finding strong purifying selection on genes involved in their replication and life-cycle. They also discovered that, regardless of the family that any the LTR-R sequences might belong, they show similar "life-histories."

“What the scientists found helps explain why these elements can, while lying quiet for millions of years, suddenly amplify within genomes while not causing more long-term harm than to take up space,” noted lead researcher Regina Baucom.

Read the paper at http://dx.doi.org/10.1101/gr.083360.108