Published in
Oxford University Press, Nucleic Acids Research, 17(38), p. 5844-5850, 2010
DOI: 10.1093/nar/gkq348
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siRNAs compete with miRNAs for methylation by HEN1 in Arabidopsis
,
Manu Agarwal,
Shengben Li,
Qingfa Wu,
Shou-Wei Ding,
Blake C. Meyers ,
Hervé Vaucheret,
Xuemei Chen
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Abstract
Plant microRNAs (miRNAs) and small interfering RNAs (siRNAs) bear a 2′-O-methyl group on the 3′-terminal nucleotide. This methyl group is post-synthetically added by the methyltransferase protein HEN1 and protects small RNAs from enzymatic activities that target the 3′-OH. A mutagenesis screen for suppressors of the partial loss-of-function hen1-2 allele in Arabidopsis identified second-site mutations that restore miRNA methylation. These mutations affect two subunits of the DNA-dependent RNA polymerase IV (Pol IV), which is essential for the biogenesis of 24 nt endogenous siRNAs. A mutation in RNA-dependent RNA polymerase 2, another essential gene for the biogenesis of endogenous 24-nt siRNAs, also rescued the defects in miRNA methylation of hen1-2, revealing a previously unsuspected, negative influence of siRNAs on HEN1-mediated miRNA methylation. In addition, our findings imply the existence of a negative modifier of HEN1 activity in the Columbia genetic background.