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Contrary to inheritance laws the scientific world has accepted for more than
100 years, some plants revert to normal traits carried by their
grandparents, bypassing genetic abnormalities carried by both parents, March
2005 by Susan A. Steeves.

These mutant parent plants apparently have hidden templates containing
genetic information from the preceding generation that can be transferred to
their offspring, even though the traits aren't evident in the parents,
according to Purdue University researchers. This discovery flies in the face
of the scientific laws of inheritance first described by Gregor Mendel in
the mid-1800s and still taught in classrooms around the world today.

"This means that inheritance can happen more flexibly than we thought in the
past," said Robert Pruitt, a Purdue Department of Botany and Plant Pathology
molecular geneticist. "While Mendel's laws that we learned in high school
still are fundamentally correct, they're not absolute.

"If the inheritance mechanism we found in the research plant Arabidopsis
exists in animals, too, it's possible that it will be an avenue for gene
therapy to treat or cure diseases in both plants and animals."

The study is published in the March 24 issue of the journal Nature.

Pruitt and collaborator Susan Lolle found that Arabidopsis in which each
parent plant had two copies of a mutant gene could produce progeny that
didn't show the parents' deformity, but rather were normal like the
grandparents. Under Mendelian laws, the offspring should have shown the same
mutation.

The first clue that the classic inheritance rules didn't always apply was
the discovery of normal flowers on some offspring of mutant plants. In the
deformed parents, the flowers were fused into tight balls. But in the
grandparents and 10 percent of the grandchildren, the buds become
1-millimeter-long, bright white flowers that fully opened and radiated out
from the center of a cluster.

"If you take this mutant Arabidopsis, which has two copies of the altered
gene, let it seed and then plant the seeds, 90 percent of the offspring will
look like the parent, but 10 percent will look like the normal
grandparents," Pruitt said. "Our genetic training tells us that's just not
possible. This challenges everything we believe.

"We've done a lot of experiments, described in this paper, that show none of
the simple explanations account for this skipping of generations by an
inherited trait."

The scientists kept the plants in isolation so they couldn't accidentally
crossbreed with plants that didn't have the mutated gene, called hothead,
that causes organ fusion like that seen in the flowers. The researchers used
molecular markers - bits of DNA that help identify and locate genes in
organisms - to determine whether a plant carried normal or mutant copies of
the genes.

"It seems that these hothead-containing plants keep a cryptic copy of
everything that was in the previous generation, even though it doesn't show
up in the DNA, it's not in the chromosome," Pruitt said. "Some other type of
gene sequence information that we don't really understand yet is modifying
the inherited traits."

Although the hothead gene tipped the researchers off to this unconventional
inheritance cycle, Pruitt believes that this particular DNA sequence is just
a trigger for the phenomenon. He suspects that a number of other genes and
the proteins they produce are involved in activating this process.

"We need to understand more about the molecular mechanics of how this
process works," Pruitt said. "Then we will know exactly what role this gene
plays."

Pruitt's team already knows that animals don't have hothead genes, either
normal or mutated, so the scientists must investigate which genes might
affect this novel inheritance in both plants and animals.

"There are probably a lot of other triggers yet to be discovered, and this
mechanism for inheritance may require a different trigger to make it work in
animals," he said.

Once scientists understand more about the mechanism, they then may be able
to manipulate it to modify genes already in plants and animals in order to
correct mutations that cause diseases and abnormal growth.

Though further research is required to learn how this form of inheritance
happens and how it can help improve plants or animals through gene therapy,
Pruitt said the discovery has opened an important new line of thinking.

The other researchers involved with this study were Jennifer Victor, a
former Purdue graduate student now at Butler University; and Jessica Young,
a botany and plant pathology laboratory technician. Lolle, a Purdue research
scientist, is currently at the National Science Foundation.

[news.uns.purdue.edu]

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