Plant retrotransposons: Turned on by stress

Virtually all genomes contain transposable elements. In some organisms, especially plants, transposable elements or sequences derived from them can exceed 50 % of genomic DNA. Some people believe that these elements are simply parasitic entities that flourish because they can out-replicate their host, the genome of which provides numerous safe havens both within and between genes [1]. According to this view, any useful role assumed by the sequences of a transposable element is rare and fortuitous. In contrast, the idea that transposable elements might flourish because they benefit their host goes back to the discovery of such elements in maize by McClintock (discussed in [2]). In this model, the deleterious effects of transposition could be minimized by maintaining active elements in a quiescent state during normal growth and development. In life-threatening situations, elements could be activated, thereby increasing the mutation rate and restructuring the genome. Populations able to diversify their genomes rapidly in this manner are thought to be more likely to survive and produce progeny.