Abstract
Posttranscriptional gene silencing via 21-nucleotide (nt) trans-acting small interfering RNAs (tasiRNAs) is a plant-specific RNA silencing mechanism. tasiRNAs are generated by RNA-DEPENDENT RNA POLYMERASE 6, SUPPRESSOR OF GENE SILENCING 3, and DICER-LIKE 4 using TAS transcripts as templates and degrade their target mRNA in a manner similar to micro-RNA. TAS gene-derived small RNAs also trigger cytosine methylation in cis together with known components of RNA-directed DNA methylation (RdDM). RdDM is known to be required for silencing of repetitive elements and transposons via a 24-nt small interfering RNA complementary to the target DNA. Plant-specific DNA-dependent RNA polymerase V (Pol V) is thought to be required for the recruitment of other RdDM components to the target region, together with the DDR complex, which contains DEFECTIVE IN RNA-DIRECTED DNA METHYLATION 1, DEFECTIVE IN MERISTEM SILENCING 3, and RNA-DIRECTED DNA METHYLATION 1. Although genome-wide studies indicate that Pol V and the DDR complex mostly share endogenous targets, the requirement for each component of RdDM at TAS genes remains obscure. Here, we investigated the involvement of components of the DDR complex in RdDM triggered by TAS gene-derived small RNAs. Our results show that methylation of the TAS3a gene was reduced in dms3 and drd1, whereas methylation of the TAS1c gene was decreased in dms3 but not in drd1. These findings indicate that Pol V and components of the DDR complex act separately in a locus-specific manner.
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Acknowledgments
We thank Steve Jacobsen for providing the double and triple mutant seeds of dcl2-1, dcl3-1, or dcl4-2. We thank Akiko Fudouji and Aeni Hosaka for DNA sequencing and assistance with plant work. We thank Helen Rothnie, Peter McKeown, and Charles Spillane for their critical reading of the manuscript and useful comments on it. This work was supported by the Japan Science and Technology Agency [PRESTO program (to TK)] and the Japan Society for the Promotion of Science [Grant-in-Aid for Scientific Research number 23616007 (to MY)].
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The authors declare that they have no conflict of interest.
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Kanno, T., Yoshikawa, M. & Habu, Y. Locus-Specific Requirements of DDR Complexes for Gene-Body Methylation of TAS Genes in Arabidopsis thaliana . Plant Mol Biol Rep 31, 1048–1052 (2013). https://doi.org/10.1007/s11105-012-0554-z
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DOI: https://doi.org/10.1007/s11105-012-0554-z