Mu killer Causes the Heritable Inactivation of the Mutator Family of Transposable Elements in Zea mays

Mu killer Causes the Heritable Inactivation of the Mutator Family of Transposable Elements in Zea mays

R. Keith Slotkin^a, Michael Freeling^a, and Damon Lisch^a
^a Department of Plant and Microbial Biology, University of California, Berkeley, California 94720

Corresponding author: Damon Lisch, Berkeley, CA 94720., dlisch{at}uclink.berkeley.edu (E-mail)

Communicating editor: D. VOYTAS

Mutations in a number of genes responsible for the maintenanceof transposon silencing have been reported. However, the initiationof epigenetic silencing of transposable elements is poorly characterized.Here, we report the identification of a single dominant locus,Mu killer (Muk), that acts to silence MuDR, the autonomous regulatorytransposon of the Mutator family of transposable elements inmaize. Muk results in the methylation of MuDR TIRs and is competentto silence one or several active MuDR elements. Silencing byMuk is not dependent on the position of the MuDR element andoccurs gradually during plant development. Transcript levelsof the MuDR transposase, mudrA, decrease substantially whenMuk is present. The other transcript encoded by MuDR, mudrB,also fails to accumulate in the poly(A) RNA fraction when MuDRand Muk are combined. Additionally, plants undergoing MuDR silencingproduce small, mudrA-homologous $~$ 26-nt RNAs, suggesting a rolefor RNA-directed DNA methylation in MuDR silencing. MuDR elementssilenced by Muk remain silenced even in plants that do not inheritMuk, suggesting that Muk is required for the initiation of MuDRsilencing but not for its maintenance.

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