Tulip tree's genome is 'molecular fossil'

The "extraordinary level of conservation" of genetic data in the tulip tree remains largely unchanged since the dinosaurs, a study suggests.

16 April 2013

The genetic data gives biologists
a glimpse into the distant past
when flowering plants first appeared

The species' genomic change is about 2,000 times slower than in humans, making it a "molecular fossil", a team of US researchers said.

The new information has affected our understanding of flowering plants' evolution, they added.
The findings have been published in the open access journal BMC Biology.

The team from the universities of Indiana and Arkansas sequenced the mitochondrial genome of the species (Liriodendron tulipifera), only to discover it had one of the slowest silent mutation rates (a process that does not affect gene function).

They added that the sequencing showed that many of the genes that had been lost during 200 million years of flowering plants' (angiosperms) evolution had been preserved.

"Based on this, it appears that the genome has been more-or-less frozen in time for millions and millions of years," explained co-author Prof Jeffrey Palmer.






Prehistoric powerhouses

• Scientific name: Liriodendron tulipifera
• Average height: 20m-30m
• Native to the eastern US, and is considered
  to be one of the region's tallest native trees
• Generally flowers in mid-summer
• Distinctive-shaped leaves,
  which are said to resemble dinosaur footprints
• Popular parkland species, as its flowers look similar to
  tulips Seeds are wind dispersed, often travelling up to
  seven times the distance of the mother tree
• The timber has a reputation of being resistant to termites

Mitochondria are found within organisms' cells and their job is to generate power. They do this by converting food stuffs into chemical energy that the organism uses to function.

In an accompanying commentary, Prof Ian Small from the University of Western Australia - who was not involved in the research - said the vast variations between the genetic data of angiosperms gleaned from mitochondrial genome sequencing made "untangling their evolutionary histories difficult".

However, he added, the paper by Prof Palmer et al turned out to be " an extremely useful window into the past".

Prof Small said the species was a member of an "early branching lineage" that was distinct from other groups that housed most of the world's crop plants, which had been the target of most sequencing efforts around the globe.

As a result of the slow mutation rate, he explained: "This 'fossilised' genome gives us some important clues as to what mitochondrial looked like (and how they functioned) as flowering plants evolved and took over the land in the time of the dinosaurs."

He added that the increasing cost-effectiveness of the sequencing process was making it easier to choose strategically informative species rather than focusing on economically important ones, ie food crops.

He explained that data gaps remained: "The coverage of early diverging plants is still from optimal, with many large and important groups still badly sampled - for example, gymnosperms and ferns."

He concluded: "I look forward to being able to analyse the next molecular 'fossil' to roll off the sequencing machines."



(source: BBC)