An RNA-dependent RNA polymerase is required for paramutation in maize

@article{Alleman2006AnRR,
  title={An RNA-dependent RNA polymerase is required for paramutation in maize},
  author={Mary M. Alleman and Lyudmila V Sidorenko and Karen M. McGinnis and Vishwas Seshadri and Jane E. Dorweiler and Joshua P. White and Kristin L Sikkink and Vicki L. Chandler},
  journal={Nature},
  year={2006},
  volume={442},
  pages={295-298}
}
Paramutation is an allele-dependent transfer of epigenetic information, which results in the heritable silencing of one allele by another. Paramutation at the b1 locus in maize is mediated by unique tandem repeats that communicate in trans to establish and maintain meiotically heritable transcriptional silencing. The mop1 (mediator of paramutation1) gene is required for paramutation, and mop1 mutations reactivate silenced Mutator elements. Plants carrying mutations in the mop1 gene also… 
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RNA-mediated trans-communication can establish paramutation at the b1 locus in maize
TLDR
A role for mop1 is uncovered in the biogenesis of a subset of microRNAs (miRNAs) and it is uncovered that it functions at the level of production of the primary miRNA transcripts.
RNA-Dependent RNA Polymerase Is Required for Enhancer-Mediated Transcriptional Silencing Associated With Paramutation at the Maize p1 Gene
TLDR
It is demonstrated that RNA-mediated gene-silencing mechanisms play key roles in p1 paramutation and the spectrum of roles for MOP1 is broadened to include tissue-specific expression patterns.
Initiation, Establishment, and Maintenance of Heritable MuDR Transposon Silencing in Maize Are Mediated by Distinct Factors
TLDR
It is shown that this gene, Mop1 (Mediator of paramutation1) codes for a putative RNA-dependent RNA polymerase, whose activity is required for the production of small RNAs that correspond to the MuDR transposon sequence, suggesting that the establishment and maintenance of MuDR silencing have distinct requirements.
Specific Tandem Repeats Are Sufficient for Paramutation-Induced Trans-Generational Silencing
TLDR
Paramutation was achieved using multiple transgenes containing the b1 tandem repeats, including events with tandem repeats of only one half of the repeat unit, demonstrating that these sequences are sufficient for paramutation and an allelic position is not required for the repeats to communicate.
RNA-directed DNA methylation prevents rapid and heritable reversal of transposon silencing under heat stress in Zea mays
TLDR
It is demonstrated that although DNA methylation is not required to maintain silencing of the MuDR element, it is essential for preventing heat-induced, stable and heritable changes in both H3K9me2 and H3k27me3 at this element, and for concomitant changes in transcriptional activity.
Paramutation in Drosophila linked to emergence of a piRNA-producing locus
TLDR
It is shown that clusters of P-element-derived transgenes that induce strong TSE can convert other homologous transgene clusters incapable of TSE into strong silencers, which transmit the acquired silencing capacity through 50 generations.
Paramutagenicity of a p1 epiallele in maize
TLDR
This work proposes a model in which P1-pr paramutation is triggered by changing epigenetic states of transposons immediately adjacent to a P2-rr enhancer sequence, which could have a significant impact on breeding agronomically important traits.
Production and Processing of siRNA Precursor Transcripts from the Highly Repetitive Maize Genome
TLDR
It is shown that RMR1 is necessary for the accumulation of a majority of 24 nt small RNAs, including those derived from Long-Terminal Repeat (LTR) retrotransposons, the most common repetitive feature in the maize genome.
A Novel Snf2 Protein Maintains trans-Generational Regulatory States Established by Paramutation in Maize
TLDR
The RNA component of maize paramutation maintains small heterochromatic-like domains that can affect the stability of nascent transcripts from adjacent genes by way of a cotranscriptional repression process, highlighting a mechanism by which alleles of endogenous loci can acquire novel expression patterns that are meiotically transmissible.
Diverse Gene-Silencing Mechanisms with Distinct Requirements for RNA Polymerase Subunits in Zea mays
TLDR
A speculative hypothesis of locus-specific deployment of Pol II, Mop2-containing Pol V, or alternative versions of Pol V with second largest subunits other than MOP2 is proposed to explain the mechanistic differences in silencing at specific loci, including one example associated with paramutation.
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References

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TLDR
The observation that mop1 affects paramutation at multiple loci, despite major differences between these loci in their gene structure, correlations with DNA methylation, and stability of the paramutant state, suggests that a common mechanism underlies paramutation.
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TLDR
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TLDR
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TLDR
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TLDR
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TLDR
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TLDR
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