[Paleopsych] Startling Scientists, Plant Fixes Its Flawed Gene
shovland at mindspring.com
Fri Mar 25 14:45:11 UTC 2005
By NICHOLAS WADE
Published: March 23, 2005
In a startling discovery, geneticists at Purdue University say they have
found plants that possess a corrected version of a defective gene inherited
from both their parents, as if some handy backup copy with the right
version had been made in the grandparents' generation or earlier.
The finding implies that some organisms may contain a cryptic backup copy
of their genome that bypasses the usual mechanisms of heredity. If
confirmed, it would represent an unprecedented exception to the laws of
inheritance discovered by Gregor Mendel in the 19th century. Equally
surprising, the cryptic genome appears not to be made of DNA, the standard
The discovery also raises interesting biological questions - including
whether it gets in the way of evolution, which depends on mutations
changing an organism rather than being put right by a backup system.
"It looks like a marvelous discovery," said Dr. Elliott Meyerowitz, a plant
geneticist at the California Institute of Technology. Dr. David Haig, an
evolutionary biologist at Harvard, described the finding as "a really
strange and unexpected result," which would be important if the observation
holds up and applies widely in nature.
The result, reported online yesterday in the journal Nature by Dr. Robert
E. Pruitt, Dr. Susan J. Lolle and colleagues at Purdue, has been found in a
single species, the mustardlike plant called arabidopsis that is the
standard laboratory organism of plant geneticists. But there are hints that
the same mechanism may occur in people, according to a commentary by Dr.
Detlef Weigel of the Max-Planck Institute for Developmental Biology in
Tubingen, Germany. Dr. Weigel describes the Purdue work as "a spectacular
The finding grew out of a research project started three years ago in which
Dr. Pruitt and Dr. Lolle were trying to understand the genes that control
the plant's outer skin, or cuticle. As part of the project, they were
studying plants with a mutated gene that made the plant's petals and other
floral organs clump together. Because each of the plant's two copies of the
gene were in mutated form, they had virtually no chance of having normal
But up to 10 percent of the plants' offspring kept reverting to normal.
Various rare events can make this happen, but none involve altering the
actual sequence of DNA units in the gene. Yet when the researchers analyzed
the mutated gene, known as hothead, they found it had changed, with the
mutated DNA units being changed back to normal form.
"That was the moment when it was a complete shock," Dr. Pruitt said.
A mutated gene can be put right by various mechanisms that are already
known, but all require a correct copy of the gene to be available to serve
as the template. The Purdue team scanned the DNA of the entire arabidopsis
genome for a second, cryptic copy of the hothead gene but could find none.
Dr. Pruitt and his colleagues argue that a correct template must exist, but
because it is not in the form of DNA, it probably exists as RNA, DNA's
close chemical cousin. RNA performs many important roles in the cell, and
is the hereditary material of some viruses. But it is less stable than DNA,
and so has been regarded as unsuitable for preserving the genetic
information of higher organisms.
Dr. Pruitt said he favored the idea that there is an RNA backup copy for
the entire genome, not just the hothead gene, and that it might be set in
motion when the plant was under stress, as is the case with those having
mutated hothead genes.
He and other experts said it was possible that an entire RNA backup copy of
the genome could exist without being detected, especially since there has
been no reason until now to look for it.
Scientific journals often take months or years to get comfortable with
articles presenting novel ideas. But Nature accepted the paper within six
weeks of receiving it. Dr. Christopher Surridge, a biology editor at
Nature, said the finding had been discussed at scientific conferences for
quite a while, with people saying it was impossible and proposing
alternative explanations. But the authors had checked all these out and
disposed of them, Dr. Surridge said.
As for their proposal of a backup RNA genome, "that is very much a
hypothesis, and basically the least mad hypothesis for how this might be
working," Dr. Surridge said.
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