A Dominant Mutation in mediator of paramutation2, One of Three Second-Largest Subunits of a Plant-Specific RNA Polymerase, Disrupts Multiple siRNA Silencing Processes

Autor: Sidorenko, Lyudmila, Dorweiler, Jane E., Cigan, A. Mark, Arteaga-Vazquez, Mario, Vyas, Meenal, Kermicle, Jerry, Jurcin, Diane, Brzeski, Jan, Cai, Yu, Chandler, Vicki L.
Jazyk: angličtina
Rok vydání: 2009
Předmět:
Zdroj: PLoS Genetics
ISSN: 1553-7404
1553-7390
Popis: Paramutation involves homologous sequence communication that leads to meiotically heritable transcriptional silencing. We demonstrate that mop2 (mediator of paramutation2), which alters paramutation at multiple loci, encodes a gene similar to Arabidopsis NRPD2/E2, the second-largest subunit of plant-specific RNA polymerases IV and V. In Arabidopsis, Pol-IV and Pol-V play major roles in RNA–mediated silencing and a single second-largest subunit is shared between Pol-IV and Pol-V. Maize encodes three second-largest subunit genes: all three genes potentially encode full length proteins with highly conserved polymerase domains, and each are expressed in multiple overlapping tissues. The isolation of a recessive paramutation mutation in mop2 from a forward genetic screen suggests limited or no functional redundancy of these three genes. Potential alternative Pol-IV/Pol-V–like complexes could provide maize with a greater diversification of RNA–mediated transcriptional silencing machinery relative to Arabidopsis. Mop2-1 disrupts paramutation at multiple loci when heterozygous, whereas previously silenced alleles are only up-regulated when Mop2-1 is homozygous. The dramatic reduction in b1 tandem repeat siRNAs, but no disruption of silencing in Mop2-1 heterozygotes, suggests the major role for tandem repeat siRNAs is not to maintain silencing. Instead, we hypothesize the tandem repeat siRNAs mediate the establishment of the heritable silent state—a process fully disrupted in Mop2-1 heterozygotes. The dominant Mop2-1 mutation, which has a single nucleotide change in a domain highly conserved among all polymerases (E. coli to eukaryotes), disrupts both siRNA biogenesis (Pol-IV–like) and potentially processes downstream (Pol-V–like). These results suggest either the wild-type protein is a subunit in both complexes or the dominant mutant protein disrupts both complexes. Dominant mutations in the same domain in E. coli RNA polymerase suggest a model for Mop2-1 dominance: complexes containing Mop2-1 subunits are non-functional and compete with wild-type complexes.
Author Summary How an individual's genes are activated or silenced is an essential question impacting all fields of biology. Usually gene expression patterns, i.e., which genes are on and which are off in different tissues and during development, are highly reproducible; and those patterns are efficiently reset in the next generation of progeny. Paramutation represents an exception to these genetic rules, in that for certain genes the silencing that is established in an individual is efficiently transmitted to their progeny. Importantly, in these subsequent generations, the silenced gene continues to silence active versions of that gene. Prior work has demonstrated that these heritable gene expression changes are not accompanied by changes in DNA sequence: they are epigenetic. Understanding mechanisms for heritable changes in gene expression has major implications for researchers studying complex traits, including diseases. In this manuscript we demonstrate that a subunit of a RNA polymerase is required for paramutation in maize and other gene silencing processes that also involve RNA–mediated chromatin changes. We show that the multiple, closely related, plant-specific RNA polymerases mediating gene silencing have diverged functions in maize. Results from our experiments suggest testable models for the role of these polymerases in multiple gene-silencing processes.
Databáze: OpenAIRE
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