Can Plants "Evolve Backwards"?

Researchers at Purdue may have discovered a revolutionary new ability of organisms to correct their DNA. Using a mutant variety of the plant Arabidopsis, they found plant offspring that had apparently corrected various mutations in their DNA.

The rate at which the corrected mutations occurred ruled out chance as the explanation. The possibility that the correction came from another similar DNA segment acting as a template was also considered and ruled out. The researchers scanned the entire genome for similar sequences without result. Also, the fact that the correction was to a single nucleotide and no flanking DNA was different from the wild-type gene makes it unlikely that a similar but not identical sequence was used as the basis for the correction.

The authors speculate that the correction mechanism is based on a cache of ancestral sequences in RNA carried in the gamete. If true this would be a powerful new evolutionary mechanism that could help to explain how organisms can evolve at observed rates. The authors further speculate that the phenomenon may be related to some type of stress-recognition system.

Assuming that gametes carry a cache of ancestral RNA templates, when an organism detects that is undergoing stress, the new mechanism may use the cached templates to "evolve backwards" by correcting recently mutated genes thereby passing to offspring the ancestral DNA sequence.

Because it is generally thought that the vast majority of DNA mutations are detrimental, such a mechanism would allow a mutation to be "tested" in one generation and corrected in the next generation if it were determined to cause stress to the organism. So the evolving organism could avoid some detrimental mutations becoming fixed in the genome. And thus the overall rate of beneficial mutation in a population would increase.

Ref: Nature 24-Mar-2005 Pg 505