An RNA-dependent RNA Polymerase is Required for Paramutation in Maize

How maize bends the rules Paramutation, first discovered in maize in the 1950s and since found in other plants, fungi, and even mice, is an inheritance pattern that breaks the rules. Most of the time Mendel's law holds sway, and gene pairs sort independently. Paramutation is an interaction in which one silent allele of a gene 'mutates' the actively expressed allele, so that it too is silenced. New work in maize now shows that paramutation is RNA-directed. Stability of the chromatin states associated with paramutation and transposon silencing requires the mop1 gene, which encodes an RNA-dependent RNA polymerase.