A new University of Georgia study, just published in Nature, demonstrates key events in plant evolution. It allows scientists to infer what the gene order may have looked like in a common ancestor of higher plants. And it shows one way plants may have differentiated from their ancestors and each other.
"By studying the completed sequence of the smallest flowering plant, Arabidopsis, we showed that most of its genes were duplicated about 200 million years ago and duplicated again about 80 million years ago," said Andrew Paterson, a UGA plant geneticist and director of the study. "The ensuing loss of 'extra genes' caused many of the differences among modern plants."
Two years ago, scientists finished the genetic sequencing of Arabidopsis, a small, weedy plant. It was a major event, the first plant to be completely sequenced. Arabidopsis had been chosen with the assumption that it would be fairly easy, since it was small. Sometimes small packages aren't so simple.
Seeded throughout its five chromosomes were thousands of genes that seemed to be "junk." When UGA scientists compared all of the genes, they found evidence of duplicated "blocks" of similar sets of genes in two, four or eight different places along the chromosomes.
It's well known that many plants contain two or more copies of most genes. But why these copies exist and when they occurred has been unknown. Their surprising abundance in the tiny, well-studied Arabidopsis indicates that genome duplications may have played a bigger evolutionary role than was previously thought.
Why were these blocks of genes duplicated? When did this happen? Answering these questions involved a lot of computerized comparing and contrasting.