A slew of scientific papers are due for publication on the Amborella genus – a plant that is of great fascination to many systematists, with previous molecular phylogenetic analyses having placed it at the base of the lineage of flowering plants. Researchers now believe they have unraveled a longstanding mystery of evolution: why flowering plants suddenly emerged on Earth, millions of years ago.
The researchers are slated to publish their findings in the Dec. 20 issue of the journal Science. As part of the Amborella Genome Sequencing Project, the research provides a full description of the analysis, alongside implications for the research of flowering plants.
Amborella (Amborella trichopoda) is an uncommon, sprawling shrub that remains endemic to the largest principal island of New Caledonia – Grand Terre. Growing to a height of approximately eight meters, the plant boasts simple evergreen leaves and produces white flowers, arranged in small clusters along its stem; the terminal inflorescences have between, approximately, two and 30 flowers.
Amborella trichopoda is considered to have stemmed from an ancient evolutionary lineage, tracing back to a common ancestor for all flowering plant life. Researchers based at a number of institutions – University of California-Riverside, University of Buffalo, University of Florida, University of Georgia and Penn State University – sought to explore the genomic sequence of the Amborella plant. In doing so, they have unearthed new evidence describing the evolutionary path that led to the huge diversity of plant life that we observe today, with over 300,000 flowering plant species currently in existence.
The scientists indicate that sequencing of the Amborella genome has yielded invaluable data, suggesting the ancestor of flowering plants – Amborella included – had undergone a “genome doubling event,” some 200 million years ago. The researchers posit many of these duplicated genes to have established new functions, some of which contributed towards the inception of floral organs.
Charles Darwin was deeply concerned by – what he perceived to be – the rapid appearance and accelerated rate of diversification of flowering plants in the mid-Cretaceous; such unprecedented emergence of modern flowers was defined as the “abominable mystery.” Claude dePamphilis, a researcher at Penn State University, briefly reflected upon how the new findings could finally explain Darwin’s conundrum:
“Genome doubling may, therefore, offer an explanation to Darwin’s ‘abominable mystery’ – the apparently abrupt proliferation of new species of flowering plants in fossil records dating to the Cretaceous period… Generations of scientists have worked to solve this puzzle.”
Through comparison of the Amborella genome to those of other modern-day flowering plants, scientists believe they can gain new insight into the genetic origins of particular traits. According to Doug Soltis of the University of Florida, since Amborella can be used as an “evolutionary reference genome,” it can also provide researchers with an understanding some of the genomic changes that occurred in other flowering plants that evolved later. On this basis, Soltis maintains that this knowledge could prove critical to future crop improvement.
Meanwhile, Joshua Der of Penn State University suggests information on the Amborella genome could be harnessed to provide clues as to the basis for the genetic difference between seed and non-seed plants.
In addition, the group established that Amborella had acquired unusual genomic characteristics, following its divergence from other flowering plants. As an example, transposable elements – sequences of DNA that can alter position within a particular genome, often resulting in a duplication event – appeared to have stabilized in the genome of Amborella. One of the researchers from the University of California-Riverside, Sue Wessler, suggests the absence of such “transposable elements,” which can influence expression of genes that encode functional proteins, may have delayed the species’ evolution.
By James Fenner