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An RNA-dependent RNA polymerase is required for paramutation in maize
Mary Alleman1, Lyudmila Sidorenko, Karen McGinnis
1Department of Plant Sciences, 303 Forbes Hall, University of Arizona, Tucson, Arizona 85721, USA.
Nature
|July 21, 2006
Summary
Mediator of paramutation1 (mop1) is an RNA-dependent RNA polymerase essential for epigenetic silencing in maize. The mop1 gene maintains repeat RNA levels, establishing heritable chromatin states for paramutation.
Area of Science:
- Epigenetics
- Plant Genetics
- Molecular Biology
Background:
- Paramutation involves heritable epigenetic silencing of alleles.
- In maize, paramutation at the b1 locus is mediated by tandem repeats.
- The mediator of paramutation1 (mop1) gene is crucial for this process.
Purpose of the Study:
- To identify and characterize the mop1 gene.
- To understand the molecular mechanism of paramutation at the b1 locus.
- To investigate the role of mop1 in epigenetic information transfer.
Main Methods:
- Map-based cloning of the mop1 gene.
- Characterization of mop1 as an RNA-dependent RNA polymerase (RDRP).
- Nuclear run-on assays to study transcription of tandem repeats.
Main Results:
- mop1 was cloned and identified as an RDRP similar to those involved in siRNA production.
- Tandem repeats at the b1 locus are transcribed from both strands.
- No siRNAs were detected, but mop1 RDRP is proposed to maintain repeat RNA levels.
Conclusions:
- The mop1 RDRP is essential for establishing and maintaining paramutation.
- mop1 likely functions by maintaining a threshold of repeat RNA for trans-acting silencing.
- This mechanism underpins heritable chromatin state changes in paramutation.
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