Wednesday, March 23, 2005

Food for thought - Ancestoral Effects on Genetics

Upending prevailing genetic theory, a team of scientists at Purdue University has discovered a mechanism in plants that allows them to correct defective genes from their parents by tapping into an ancestral data bank of healthy genetic material.

In essence, the plants back up the evolutionary path and use past genes to restore traits that would otherwise be lost, according to a study published Tuesday in the online version of the journal Nature.

The finding proposes "an extraordinary view of inheritance," the scientists said in their paper.

The mechanism appears to be a way for self-fertilizing plants, which are more likely to suffer from the negative consequences of inbreeding, to maintain a healthy level of genetic diversity and increase their chances of survival.

It could also be a way for plants to adapt to changing environmental conditions by having a store of diverse traits at their disposal, the scientists said.

The proposal offers a radical addition to the widely embraced laws of Mendelian genetics, which date back to the mid-1800s. They hold that plants and animals inherit only two copies of a gene — one from each parent. If both copies were defective, a plant would have no ability to correct the error.

"This means that inheritance can happen more flexibly than we thought in the past," said Robert Pruitt, a molecular geneticist who co-authored the paper. "While Mendel's laws that we learned in high school are still fundamentally correct, they're not absolute."

If the newly discovered mechanism is also found to be at work in people, "it's possible that it will be an avenue for gene therapy to treat or cure diseases in both plants and animals," Pruitt said.

The Purdue scientists happened upon their discovery by accident. They were intending to study a deformed version of the Arabidopsis plant, a member of the mustard family.

Their particular variety produced flowers that were fused into tight balls, a consequence of the plants' having two defective copies of a gene dubbed "hothead."

Breeding the plants should produce only offspring that are also deformed. But the scientists were startled to see that 10% of the offspring produced normal flowers that radiated out from the center of a cluster.

They conducted a series of experiments that indicated the bright white flowers were not the result of accidental cross-pollination or other contact with normal seeds.

The plants "can recover DNA variants that have come from one of their great-grandparents, even if their immediate parent did not contain the variant," wrote molecular biologists Detlef Weigel and Gerd Jurgens in an accompanying article.

The researchers said the plants must contain a normal version of the hothead gene, although they searched the plants' genomes and were unable to find it.

That has led them to believe that the genetic information could be contained in the plant's RNA, a close cousin to DNA that is thought to be a less reliable vessel of genetic information.

Each of the steps necessary for RNA to modify the genes in DNA has already been demonstrated in other research, the scientists said.


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