New clues to evolution of flowering plants

Never mind the selfish gene – the cellular family history of the oldest living species of flowering plants is marked by enough sex and gluttony to earn a place in Shakespeare’s folio.

The powerhouse organelles inside cells of Amborella trichopoda, a woody shrub that grows only in the humid jungles of New Caledonia in the South Pacific, gobbled up and retained the entire genome from the equivalent organelles of four different species, three of moss and one of algae, according to a study of the plant’s mitochondrial DNA published in the journal Nature.

The results are the product of a years-long effort to sequence the full genome of the plant, a crucial step in solving what Charles Darwin once called “the abominable mystery” – the sudden flourishing long ago of several hundred thousand species of flowering plants. An analysis of the nuclear DNA of the species revealed that the plant is the equivalent of the animal kingdom’s duck-billed platypus – a solitary sister left behind more than 100 million years ago by what became a panoply of flowering, or fruiting, plants.

The genome map, undertaken by the Amborella Genome Project, an international consortium of universities, enabled researchers to infer the genetic makeup of the most recent common ancestor of A. trichopoda. It found that this ancestor likely evolved after an event that doubled its genome roughly 200 million years ago. Such an event could help explain what so baffled the father of evolutionary theory, the researchers said.

The map of the genome also serves as a reference point for explaining the evolution of many of the subsequent species that form the backbone of the human food chain.

But enough about nuclear DNA – let’s get to the sex and gluttony. Researchers who mapped the genome of the plant’s mitochondria, the organelles that are the energy factories inside cells, were stunned at its size and diversity and by evidence of some intracellular shenanigans.

Jeffrey D. Palmer, an Indiana University evolutionary biologist and author of the mitochondrial DNA paper, said. “There’s not another genome in any organism of any type like this. No one has found this scale of horizontal DNA transfer even in a bacterium, where it’s really common. No one has found whole genomes, much less four of them, taken up by horizontal transfer.”

The plant’s mitochondria retain a kind of fossil record largely absent in other plant species. The foreign DNA amounts to about six genomes, at least four of them acquired in whole.

– Los Angeles Times