title: Four plant Dicers mediate viral small RNA biogenesis and DNA virus induced silencing.
abstract: Like other eukaryotes, plants use DICER-LIKE (DCL) proteins as the central enzymes of RNA silencing, which regulates gene expression and mediates defense against viruses. But why do plants like Arabidopsis express four DCLs, a diversity unmatched by other kingdoms? Here we show that two nuclear DNA viruses (geminivirus CaLCuV and pararetrovirus CaMV) and a cytoplasmic RNA tobamovirus ORMV are differentially targeted by subsets of DCLs. DNA virus-derived small interfering RNAs (siRNAs) of specific size classes (21, 22 and 24 nt) are produced by all four DCLs, including DCL1, known to process microRNA precursors. Specifically, DCL1 generates 21 nt siRNAs from the CaMV leader region. In contrast, RNA virus infection is mainly affected by DCL4. While the four DCLs are partially redundant for CaLCuV-induced mRNA degradation, DCL4 in conjunction with RDR6 and HEN1 specifically facilitates extensive virus-induced silencing in new growth. Additionally, we show that CaMV infection impairs processing of endogenous RDR6-derived double-stranded RNA, while ORMV prevents HEN1-mediated methylation of small RNA duplexes, suggesting two novel viral strategies of silencing suppression. Our work highlights the complexity of virus interaction with host silencing pathways and suggests that DCL multiplicity helps mediate plant responses to diverse viral infections.
authors.affiliation: Institute of Botany, University of Basel, Schönbeinstrasse 6, 4056 Basel, Switzerland.
authors.forename: Todd
authors.initials: T
authors.lastname: Blevins
authors.forename: Rajendran
authors.initials: R
authors.lastname: Rajeswaran
authors.forename: Padubidri V
authors.initials: PV
authors.lastname: Shivaprasad
authors.forename: Daria
authors.initials: D
authors.lastname: Beknazariants
authors.forename: Azeddine
authors.initials: A
authors.lastname: Si-Ammour
authors.forename: Hyun-Sook
authors.initials: HS
authors.lastname: Park
authors.forename: Franck
authors.initials: F
authors.lastname: Vazquez
authors.forename: Dominique
authors.initials: D
authors.lastname: Robertson
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 / Q000201:enzymology / Q000235:genetics / Q000821:virology; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D017796:Caulimovirus / Q000235:genetics; D017791:Geminiviridae / Q000235:genetics; D020868:Gene Silencing; D035683:MicroRNAs / Q000378:metabolism; D009154:Mutation; D010935:Plant Diseases / Q000821:virology*; D010942:Plant Viruses / Q000235:genetics*; D012330:RNA, Double-Stranded / Q000378:metabolism; D034741:RNA, Small Interfering / Q000145:classification / Q000378:metabolism*; D012367:RNA, Viral / Q000145:classification / Q000378:metabolism; D043244:Ribonuclease III / Q000235:genetics / Q000378:metabolism*; D017898:Tobamovirus / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D035683:MicroRNAs; D012330:RNA, Double-Stranded; D034741:RNA, Small Interfering; D012367:RNA, Viral; D043244:Ribonuclease III