title: Degradation of the antiviral component ARGONAUTE1 by the autophagy pathway.
abstract: Posttranscriptional gene silencing (PTGS) mediated by siRNAs is an evolutionarily conserved antiviral defense mechanism in higher plants and invertebrates. In this mechanism, viral-derived siRNAs are incorporated into the RNA-induced silencing complex (RISC) to guide degradation of the corresponding viral RNAs. In Arabidopsis, a key component of RISC is ARGONAUTE1 (AGO1), which not only binds to siRNAs but also carries the RNA slicer activity. At present little is known about posttranslational mechanisms regulating AGO1 turnover. Here we report that the viral suppressor of RNA silencing protein P0 triggers AGO1 degradation by the autophagy pathway. Using a P0-inducible transgenic line, we observed that AGO1 degradation is blocked by inhibition of autophagy. The engineering of a functional AGO1 fluorescent reporter protein further indicated that AGO1 colocalizes with autophagy-related (ATG) protein 8a (ATG8a) positive bodies when degradation is impaired. Moreover, this pathway also degrades AGO1 in a nonviral context, especially when the production of miRNAs is impaired. Our results demonstrate that a selective process such as ubiquitylation can lead to the degradation of a key regulatory protein such as AGO1 by a degradation process generally believed to be unspecific. We anticipate that this mechanism will not only lead to degradation of AGO1 but also of its associated proteins and eventually small RNAs.
authors.affiliation: Institut de Biologie Moléculaire des Plantes, Centre National de la Recherche Scientifique, Unité Propre de Recherche 2357,  Conventionné avec l'Université de Strasbourg, 67084 Strasbourg,  France.
authors.forename: Benoît
authors.initials: B
authors.lastname: Derrien
authors.forename: Nicolas
authors.initials: N
authors.lastname: Baumberger
authors.forename: Mikhail
authors.initials: M
authors.lastname: Schepetilnikov
authors.forename: Corrado
authors.initials: C
authors.lastname: Viotti
authors.forename: Julia
authors.initials: J
authors.lastname: De Cillia
authors.forename: Véronique
authors.initials: V
authors.lastname: Ziegler-Graff
authors.forename: Erika
authors.initials: E
authors.lastname: Isono
authors.forename: Karin
authors.initials: K
authors.lastname: Schumacher
authors.forename: Pascal
authors.initials: P
authors.lastname: Genschik
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060565:Argonaute Proteins / Q000235:genetics / Q000378:metabolism*; D001343:Autophagy; D020868:Gene Silencing; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism; D010942:Plant Viruses / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism / Q000821:virology; D059748:Proteolysis; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D012367:RNA, Viral / Q000235:genetics / Q000378:metabolism; D034743:RNA-Induced Silencing Complex / Q000235:genetics / Q000378:metabolism; D054875:Ubiquitination / Q000235:genetics
chemical_list: C117457:AGO1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D060565:Argonaute Proteins; D035683:MicroRNAs; D018749:RNA, Plant; D012367:RNA, Viral; D034743:RNA-Induced Silencing Complex