Plants display 'molecular amnesia'(ated. These are the genes carried by tra...)

The researchers' experiments with corn technically known as "maize" suggest the propensity to maintain epigenetic states can vary depending on the position of the transposons within the genome.

Many organisms, from worms to humans to plants, have learned to tame transposons by epigentically "silencing" them: if they can't express their genes they can't jump. If they can't jump for long enough, their DNA sequence slowly accumulates errors, and they become molecular fossils. Most transposons in most organisms are silenced in this way, but some remain quite active.

In previous studies from the laboratory of two of the article's authors, UC Berkeley professors Damon Lisch and Michael Freeling, with the support of the National Science Foundation at UC Berkeley, epigenetic silencing was triggered in maize. Once triggered, the maize plant "remembers," and keeps the transposon "silenced" generation after generation, even after the trigger is lost.

"However, we have found that at some positions in the genome, this is not the case. At these positions, although the trigger works fine, and the transposon is silenced, once the trigger is lost, the transposon reawakens," said Jaswinder Singh, a professor in the Plant Sciences Department at McGill University, and lead author of the new article. The study, "A Position Effect on the Heritability of Epigenetic Silencing," was published in October in the journal PLoS Genetics.

This "molecular amnesia" has never before been documented in plants and no one has seen it associated with a particular position in the genome of any species before. These data suggest the epigenetic landscape of plant genomes may be more subtle and interesting than previously thought, with the ability
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