LTR-retrotransposons and MITEs: important players in the evolution of plant genomes.

Retrotransposons are an abundant and ancient component of plant genomes, yet recent evidence indicates that element activity in many modern plants is restricted to times of stress. Stress activation of plant retrotransposons may be a significant factor in somaclonal variation, in addition to providing an important means to isolate new active elements. Long terminal repeat retrotransposons and a second class of elements we have called miniature inverted-repeat transposable elements (MITEs) have recently been found to be associated with the genes of diverse plants where some contribute regulatory sequences. Because of their sequence diversity and small size, MITEs may be a valuable evolutionary tool for altering patterns of gene expression.