Embargoed until: 2:00 P.M., EST
NSF PR 01-104 - December 13, 2001
Researchers Find Closest Living Relative of First
Land Plants
Some 470 million years ago, the first land plants emerged
from prehistoric waters, put down roots in soil and
ended up ruling the plant world. But scientists haven't
been certain about the family history of those pioneer
plants.
By studying gene sequences of common fresh water algae,
a team of University of Maryland researchers, funded
by the National Science Foundation (NSF) has traced
this family tree and identified a group of algae that
are the closest living relatives of the first land
plants. The scientists have moved a step closer to
understanding how land plants evolved and came to
dominate the terrestrial biosphere.
"What used to be a very short story - land plants evolved
from aquatic algae - just became a much more interesting
narrative," said James Rodman, program director in
NSF's division of environmental biology. "The new
details in this part of the Tree of Life will guide
research on how photosynthesizing organisms conquered
the land."
In a study published in the Dec. 14 issue of the journal
Science, Maryland scientist Charles Delwiche
and doctoral student Kenneth Karol confirm that the
closest living relative of the first land plants is
a group of green algae called the Charales, which
survives today in fresh water around the world.
"Science has long believed that land plants are derived
from primeval algae that became adapted to live on
land, but we weren't sure exactly how this happened,
or which living algae were most closely related to
land plants," said Delwiche. "It's an important part
of the Tree of Life that has been unresolved."
Although both the Charales and land plants can be traced
back in the fossil record over a period of more than
400 million years, their common ancestor has been
extinct for even longer and hasn't been identified
in the fossil record.
"Our data confirm that land plants and the Charales
both evolved from a common ancestor that was a fairly
complex organism," said Delwiche. "We now can make
specific inferences about what this organism looked
like. It wasn't just some sort of amorphous pond scum.
It was made up of branching threads and reproduced
with eggs and sperm."
Scientists have thought that Charales and another group
of algae called the Coleochaetales were almost equal
cousins of the first land plants. Both groups share
with land plants similar characteristics of growth,
reproduction and cell division. But it wasn't until
Delwiche and Karol, along with collaborator Richard
M. McCourt at the Academy of Natural Sciences in Philadelphia
and University of Maryland student Matthew T. Cimino,
studied the DNA sequences of four genes from 40 different
plants and algae that the lineage could be traced
with certainty.
"Plants didn't write diaries or letters for us to study,
but they do have genetic sequences that can reveal
their evolutionary history," said Karol. "The DNA
of the Coleochaeteles shows many similar characteristics
to land plants, but the Charales are even more closely
related. The genes we examined show not only that
the Charales are related to the first land plants,
but that they are the closest living relatives."
"These findings can help us understand what properties
allowed land plants to dominate the biosphere," said
Delwiche. "It's really exciting to know that we still
have plants that look like the ancestors that were
underfoot when the dinosaurs roamed the earth."
The study was funded by the "Partnership for Enhancing
Expertise in Taxonomy" program of the National Science
Foundation.
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