Maize Transposable Elements in Development and Evolution

Transposable elements were first discovered in maize by BarbaraMcClintock more than 40 years ago. Today it is apparent thattransposable elements are a common component of the geneticmaterial in virtually all organisms. The best studied maizetransposable elements belong to the Activator-Dissociation andSuppressor-mutator families. They are short DNA sequences thatconsist of genes required for mobility and regulation. Boththe expression and the mobility of transposable elements areregulated in development by a mechanism that relies on the methylationof element sequences critical for expression. Elements can bestably inactivated by the same mechanism, persisting in thegenome in a cryptic form for long periods. The ability of thehost organism to regulate the highly mutagenic transposableelements may be critical to their survival, as well as theirutility as agents of genomic change.