Heritable transposon silencing initiated by a naturally occurring transposon inverted duplication.

ABSTRACT

It has been suggested that gene silencing evolved as a defense against genomic parasites such as transposons. This idea is based on analysis of mutations that reactivate transposons that are stably silenced they affect maintenance rather than initiation of silencing. Here we describe the cloning and characterization of a naturally occurring locus able to heritably silence the otherwise highly active MuDR transposon in maize. This locus, Mu killer (Muk), results from the inverted duplication of a partially deleted autonomous MuDR element located at the breakpoint of a genomic deletion. Muk produces a hybrid hairpin transcript that is processed into small RNAs, which are amplified when the target MuDR transcript is present. Muk provides the first example of a naturally occurring transposon derivative capable of initiating the heritable silencing of an active transposon family. Further, transposon-generated inverted duplications may be important for the generation of double-stranded RNAs used in gene silencing.