Here at s8int.com, we don't know how many of you really want to read through two articles on a weed to get to the crux of the problem that these findings present for Evolutionists. Our eyes did get a little heavy but we never actually nodded off.
Mutation as the mechanism for the process of evolution has already been virtually eliminated as far as we are concerned but this may be the final nail in the coffin. It seems as though contrary to all previous thought, organisms like this plant may have the ability to overcome mutations in their genes and restore their genetic codes back to that of prior generations. In other words, a previously unkown method of error correction exists that overcomes the Medellian processes of inheritance. Can you imagine how the "evolutionary process" could have "created" a backup mechanism for overcoming genetic mutations --using the process of mutation? Neither can we. We think that ability comes from the original designer: GOD.
In a discovery that has flabbergasted geneticists, researchers have shown that plants can overwrite the genetic code they inherit from their parents, and revert to that of their grandparents.
The finding challenges textbook rules of inheritance, which state that children simply receive combinations of the genes carried by their parents. The principle was famously established by Austrian monk Gregor Mendel in his nineteenth-century studies on pea plants.
The study, published this week in Nature1, shows that not all genes are so well behaved. It suggests that plants, and perhaps other organisms including humans, might possess a back-up mechanism that can bypass unhealthy sequences from their parents and revert to the healthier genetic code possessed by their grandparents or great-grandparents.
Robert Pruitt and his colleagues at Purdue University in West Lafayette, Indiana, hit upon the discovery when studying a particular strain of the cress plant Arabidopsis, which carries a mutation in both copies of a gene called HOTHEAD. In mutated plants, the petals and other flower parts are abnormally fused together.
Because these plants pass the mutant gene on to their offspring, conventional genetics dictates that they will also have fused flowers. Not so: Pruitt's team has known for some time that around 10% of the offspring have normal flowers.
Using genetic sequencing, the researchers showed that this second generation of plants had rewritten the DNA sequence of one or both of their HOTHEAD genes. They had replaced the abnormal code of their parents with the regular code possessed by earlier generations.
And when the team studied numerous other genes, it found that the plants had often edited those back to their ancestral form too. "It was a huge surprise," Pruitt says.
The discovery has left geneticists reeling. "It's really quite stunning," says Detlef Weigel, who studies plant genetics at the Max Planck Institute for Developmental Biology in Tübingen, Germany. "It's a mechanism that no one had any idea existed."
And geneticist Steven Jacobsen at the University of California, Los Angeles, sums it up even more succinctly. "It's really weird," he says.
Pruitt and other researchers are struggling to explain exactly how the plants could rewrite their genetic code. To do that, they need a template (a version of their grandparents' code) that can be passed from one generation to the next.
One possibility is that the plants use an extra copy of a gene perched elsewhere in their DNA. But this seems unlikely, because the team found that the plants can rewrite the code of genes that have no similar copies elsewhere in the genome.
Instead, Pruitt speculates that the plants carry a previously undiscovered store of the related molecule RNA, that acts as a backup copy of DNA. Such molecules could be passed into pollen or seeds along with DNA and used as a template to correct certain genes. "It's the most likely explanation," Weigel agrees.
Pruitt speculates that this type of gene correction goes on in Arabidopsis under normal conditions, just very rarely. He suggests that it is ramped up when the HOTHEAD gene is mutated, perhaps because the plant becomes stressed.
Indeed, the process could exist because it helps plants to survive whenever they find themselves in difficult condition, such as when water or nutrients become scarce. Such stress could trigger plants to revert to the genetic code of their ancestors, which is perhaps more hardy than that of their parents. To test this, Pruitt is examining whether stressful situations do indeed prompt the same phenomenon.
A similar process might even go on in humans. This is suggested by rare cases of children who inherit disease-causing mutations but show only mild symptoms, perhaps because some of their cells have reverted to a normal and healthier genetic code.
If humans do correct their genes in this way, Pruitt suggests that the procedure might be usefully hijacked by researchers or doctors. They might be able to identify the RNA molecules that carry out the repair and use them to correct harmful mutations in patients.
But for now, Pruitt and other researchers in the field are expecting the paper to prompt a lot of scepticism. "The immediate response is that they must have made a mistake," Weigel says, "but I don't think so."
Mendelian inheritance, the central tenet of genetics, is under attack from a few scrawny weeds that have not read the textbooks. The weeds are somehow inheriting DNA sequences from their grandparents that neither of their parents possessed - which is supposed to be impossible.
The orthodox view is that genes are passed down in the form of DNA, and all organisms have to make do with this parental DNA inheritance, mutations and all. Chemical or structural modifications to DNA can switch off genes, and these changes can pass from generation to generation, a phenomenon called epigenesis. But epigenetic changes do not alter the actual sequence of DNA.
Yet that is what seems to occur in the weedy cress Arabidopsis thaliana, the workhorse of plant biologists. Cress with two mutant copies of one gene seem to be able to correct the DNA they pass on, ensuring that at least a few of their offspring revert to normal.
Robert Pruitt, whose team at Purdue University in West Lafayette, Indiana, US, made this extraordinary discovery, thinks that the mutant genes are being repaired using RNA templates inherited from earlier generations.
Other biologists are astonished by the findings. "It's amazing," says David Baulcombe, an expert on plant RNA at the John Innes Centre in Norwich, UK. "The notion that RNA carries the information almost seems like the only way it could happen."
It is possible that the phenomenon is limited to this one plant. But in Nature (vol 434, p 505), Pruitt's team speculates that it might be a more widespread mechanism that allows plants to "experiment" with new mutations while keeping RNA spares as a back-up.
If the mutations prove harmful, some plants in the next generation revert to their grandparents' DNA sequence with the help of the RNA. "It does make sense," Pruitt says.
Such a mechanism would be especially useful to plants that self-pollinate and so are not as genetically variable as other plants. But it might happen in all plants and even animals.
Pruitt's team made the discovery after finding that some Arabidopsis refused to "breed true". To Pruitt's irritation as many as 1 in 10 of the offspring grew normally despite their parents having a mutation in both copies of the hothead gene, which causes petals and leaves to stick to one another. He assumed that normal seeds or pollen were contaminating his trials.
But a series of experiments ruled out contamination. They also ruled out other possibilities, including the gene spontaneously mutating back to the normal form, the existence of more than two copies of the hothead gene, or closely related DNA sequences providing a template for repairs.
Eventually, Pruitt was left with one, unbelievable explanation: the normal offspring were somehow acquiring genetic information from ancestors other than their parents.
"It was our view that it was heresy when we started working on it, but we've had time to get used to the idea now," he says. "I'd say I've been the biggest sceptic all the way along, but every experiment has been done to find a conventional explanation and it's as foolproof as we can make it. I have every confidence in the data, but I'll feel better about it when other people have seen similar things."
The team has also found that in hothead mutants, other faulty genes mysteriously revert to the sequence of earlier generations too. It may be that the phenomenon is caused by the hothead mutation and restricted to plants that carry it, says Ottoline Leyser, who studies plant developmental genes at the University of York in the UK. "People have been working on mutants for years, and they all behave in a Mendelian way," she says.
"It's possible it is just related to this one gene," agrees Pruitt. "We can't rule it out, but I think it's unlikely." Other researchers may simply have dismissed mutants that revert to an ancestral form as the product of contamination, Leyser says. "Maybe it has been under the radar."
Pruitt's team is now trying to find the stash of RNAs from earlier generations that might provide the templates for repair, and work out how it is passed down. "My guess is that it is in the nucleus somehow, or hitchhikes on chromosomes, but that's just speculation," he says.
While the search goes on, Pruitt hopes other biologists will hunt for evidence of the phenomenon in plants, animals and even humans. "If we can understand how these templates are used, we might be able to make our own to order," he says. That might help improve existing methods for repairing genes, which are not yet efficient enough to be used to treat genetic diseases.
Journal reference: Nature (vol 434, p 505)