Newly sequenced genome reveals why flower may have come to be

Amborella, a plant that hails from an ancient evolutionary lineage, may be the reason why flowers exist. Scientists who sequenced its genome say its DNA provides conclusive evidence that the ancestor of all flowering plants, including Amborella, evolved following a "polyploidy event,” during which an organism’s entire genome is duplicated. It happened about 200 million years ago.

Because redundant copies of genes can evolve to develop new functions, this doubling may be behind "Darwin's abominable mystery" — the apparently abrupt proliferation of new varieties of flowering plants in fossil records dating to the Cretaceous period, about 145 million years ago.

Some duplicated genes were lost over time but others took on new functions, including contributions to the development of floral organs. The research was led by scientists at Penn State University, the University at Buffalo, the University of Florida, the University of Georgia and the University of California, Riverside.

A paper by the Amborella Genome Sequencing Project that includes a full description of the analyses performed, as well as implications for flowering plant research, was published in the journal Science on Dec. 20. The article is among three on different research areas related to the Amborella genome that will be published in the same issue of the journal.

Of more than 300,000 flowering plant species alive today, Amborella (Amborella trichopoda) is unique as the sole survivor of an ancient evolutionary lineage that traces back to the last common ancestor of all flowering plants, according to the research team. The plant is a small understory tree found only on the main island of New Caledonia in the South Pacific. This heritage gives Amborella a special role in the study of flowers, said Victor Albert, UB professor of biological sciences, who played a key role in leading the research effort.

"In the same way that the genome sequence of the platypus — a survivor of an ancient lineage — can help us study the evolution of all mammals, the genome sequence of Amborella can help us learn about the evolution of all flowers," Albert said.

Generations of scientists have worked to solve the puzzle of why flowering plants suddenly proliferated in fossil records, said Claude dePamphilis of Penn State University, another lead investigator. Though whole genome duplication might sound strange, many species have evidence of doubling in their DNA. The ancient ancestor of all vertebrates — including humans — underwent a polyploidy event, Albert said. Genome doubling may also be responsible for a great expansion in the varieties of ray-finned fish on Earth.

The Amborella genome will provide scientists with a new tool for studying the genetic history of all flowering plants, and how genome duplication may have played a role in the evolution of traits like drought-resistance or fruit maturation. This is particularly important because flowers account for all major food crop species, such as tomatoes, potatoes, rice, apples, avocados, and soy.

“By comparing the DNA of various species to Amborella, we will be able to learn how important traits evolved,” Albert said. “What makes Amborella an excellent point of reference for such comparisons is that it sits near the base of the evolutionary tree of life of flowering plants,” he said. “It allows us to triangulate — to make comparisons between plants that came later on by comparing each different species to Amborella.”

The complete genome sequence of Amborella has been deposited in Genbank — the U.S. National Institutes of Health database of publicly available gene sequences — and also is available in the Amborella Genome Database.

In addition to researchers at Penn State University, the University at Buffalo, the University of Florida, the University of Georgia and the University of California, Riverside, the paper's authors include scientists from other universities in the United States, Canada, Mexico, China, Korea, Taiwan, Singapore, Germany, Italy, Denmark, France and New Caledonia. The work was funded by the National Science Foundation's Plant Genome Research Program.
More detailed information on the research consortium's findings can be viewed in a Penn State news release.

Source: University of Bufflalo

Photo: Sangtae Kim