title: The CaMV transactivator/viroplasmin interferes with RDR6-dependent trans-acting and secondary siRNA pathways in Arabidopsis.
abstract: Several RNA silencing pathways in plants restrict viral infections and are suppressed by distinct viral proteins. Here we show that the endogenous trans-acting (ta)siRNA pathway, which depends on Dicer-like (DCL) 4 and RNA-dependent RNA polymerase (RDR) 6, is suppressed by infection of Arabidopsis with Cauliflower mosaic virus (CaMV). This effect was associated with overaccumulation of unprocessed, RDR6-dependent precursors of tasiRNAs and is due solely to expression of the CaMV transactivator/viroplasmin (TAV) protein. TAV expression also impaired secondary, but not primary, siRNA production from a silenced transgene and increased accumulation of mRNAs normally silenced by the four known tasiRNA families and RDR6-dependent secondary siRNAs. Moreover, TAV expression upregulated DCL4, DRB4 and AGO7 that mediate tasiRNA biogenesis. Our findings suggest that TAV is a general inhibitor of silencing amplification that impairs DCL4-mediated processing of RDR6-dependent double-stranded RNA to siRNAs. The resulting deficiency in tasiRNAs and other RDR6-/DCL4-dependent siRNAs appears to trigger a feedback mechanism that compensates for the inhibitory effects.
authors.affiliation: Institute of Botany, University of Basel, Schönbeinstrasse 6, 4056 Basel, Switzerland.
authors.forename: Padubidri V
authors.initials: PV
authors.lastname: Shivaprasad
authors.forename: Rajendran
authors.initials: R
authors.lastname: Rajeswaran
authors.forename: Todd
authors.initials: T
authors.lastname: Blevins
authors.forename: James
authors.initials: J
authors.lastname: Schoelz
authors.forename: Frederick
authors.initials: F
authors.lastname: Meins
authors.forename: Thomas
authors.initials: T
authors.lastname: Hohn
authors.forename: Mikhail M
authors.initials: MM
authors.lastname: Pooggin
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000821:virology*; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors*; D017796:Caulimovirus / Q000378:metabolism; D034622:RNA Interference; D012322:RNA Precursors / Q000096:biosynthesis; D012330:RNA, Double-Stranded / Q000096:biosynthesis; D034741:RNA, Small Interfering / Q000096:biosynthesis* / Q000737:chemistry; D012324:RNA-Dependent RNA Polymerase / Q000037:antagonists & inhibitors*; D043244:Ribonuclease III; D012260:Ribonucleases / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism*; D019076:Transgenes; D014764:Viral Proteins / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D012322:RNA Precursors; D012330:RNA, Double-Stranded; D034741:RNA, Small Interfering; D015534:Trans-Activators; D014764:Viral Proteins; C095687:gene VI protein, Cauliflower mosaic virus; C065790:viroplasmin protein, Cauliflower mosaic virus; C514575:RDR6 protein, Arabidopsis; D012324:RNA-Dependent RNA Polymerase; C504982:DCL4 protein, Arabidopsis; D012260:Ribonucleases; D043244:Ribonuclease III
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