title: Cytoplasmic assembly and selective nuclear import of Arabidopsis Argonaute4/siRNA complexes.
abstract: In plants, DNA methylation can be mediated by a class of Argonaute4 (AGO4)-associated heterochromatic siRNAs (hc-siRNAs), through a pathway termed RNA-directed DNA methylation (RdDM). It has been thought that RdDM is solely a nuclear process, as both the biogenesis and functioning of hc-siRNAs take place in the nucleus. In this study, we unexpectedly found that hc-siRNAs are predominantly present in the cytoplasm. We demonstrated that AGO4 is loaded with hc-siRNAs in the cytoplasm and the formation of mature AGO4/siRNA complexes requires HSP90 and the cleavage activity of AGO4. Intriguingly, siRNA binding facilitates the redistribution of AGO4 into the nucleus, likely through inducing conformational change that leads to the exposure of the nuclear localization signal (NLS). Our findings reveal an unsuspected cytoplasmic step in the RdDM pathway. We propose that selective nuclear import of mature AGO4/siRNA complexes is a key regulatory point prior to the effector stage of RdDM.
authors.affiliation: State Key Laboratory of Rice Biology, Institute of Biotechnology, Zhejiang University, Zhejiang 310029, China.
authors.forename: Ruiqiang
authors.initials: R
authors.lastname: Ye
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Taichiro
authors.initials: T
authors.lastname: Iki
authors.forename: Chang
authors.initials: C
authors.lastname: Liu
authors.forename: Yang
authors.initials: Y
authors.lastname: Wu
authors.forename: Masayuki
authors.initials: M
authors.lastname: Ishikawa
authors.forename: Xueping
authors.initials: X
authors.lastname: Zhou
authors.forename: Yijun
authors.initials: Y
authors.lastname: Qi
mesh_terms: D021581:Active Transport, Cell Nucleus; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060565:Argonaute Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D019175:DNA Methylation; D018744:DNA, Plant / Q000235:genetics / Q000378:metabolism; D020868:Gene Silencing; D018841:HSP90 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D008954:Models, Biological; D019913:Nuclear Localization Signals; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism*
chemical_list: C471209:AGO4 protein, Arabidopsis; D029681:Arabidopsis Proteins; D060565:Argonaute Proteins; D018744:DNA, Plant; D018841:HSP90 Heat-Shock Proteins; D019913:Nuclear Localization Signals; D018749:RNA, Plant; D034741:RNA, Small Interfering