title: Infection cycle of Artichoke Italian latent virus in tobacco plants: meristem invasion and recovery from disease symptoms.
abstract: Nepoviral infections induce recovery in fully expanded leaves but persist in shoot apical meristem (SAM) by a largely unknown mechanism. The dynamics of infection of a grapevine isolate of Artichoke Italian latent virus (AILV-V, genus Nepovirus) in tobacco plants, including colonization of SAM, symptom induction and subsequent recovery of mature leaves from symptoms, were characterized. AILV-V moved from the inoculated leaves systemically and invaded SAM in 7 days post-inoculation (dpi), remaining detectable in SAM at least up to 40 dpi. The new top leaves recovered from viral symptoms earliest at 21 dpi. Accumulation of viral RNA to a threshold level was required to trigger the overexpression of RDR6 and DCL4. Consequently, accumulation of viral RNA decreased in the systemically infected leaves, reaching the lowest concentration in the 3rd and 4th leaves at 23 dpi, which was concomitant with recovery of the younger, upper leaves from disease symptoms. No evidence of virus replication was found in the recovered leaves, but they contained infectious virus particles and were protected against re-inoculation with AILV-V. In this study we also showed that AILV-V did not suppress initiation or maintenance of RNA silencing in transgenic plants, but was able to interfere with the cell-to-cell movement of the RNA silencing signal. Our results suggest that AILV-V entrance in SAM and activation of RNA silencing may be distinct processes since the latter is triggered in fully expanded leaves by the accumulation of viral RNA above a threshold level rather than by virus entrance in SAM.
authors.affiliation: Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Bari, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Santovito
authors.affiliation: Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Bari, Italy; Istituto di Virologia vegetale del Consiglio Nazionale della Ricerca, Unità Operativa di Supporto di Bari, Bari, Italy.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Mascia
authors.affiliation: Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland.
authors.forename: Shahid A
authors.initials: SA
authors.lastname: Siddiqui
authors.affiliation: Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Bari, Italy.
authors.forename: Serena Anna
authors.initials: SA
authors.lastname: Minutillo
authors.affiliation: Department of Agricultural Sciences, University of Helsinki, Helsinki, Finland.
authors.forename: Jari P T
authors.initials: JP
authors.lastname: Valkonen
authors.affiliation: Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università degli Studi di Bari Aldo Moro, Bari, Italy; Istituto di Virologia vegetale del Consiglio Nazionale della Ricerca, Unità Operativa di Supporto di Bari, Bari, Italy.
authors.forename: Donato
authors.initials: D
authors.lastname: Gallitelli
mesh_terms: D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D054884:Host-Pathogen Interactions / Q000235:genetics; D008018:Life Cycle Stages; D018519:Meristem / Q000821:virology; D010641:Phenotype; D010935:Plant Diseases / Q000235:genetics / Q000821:virology*; D018515:Plant Leaves / Q000821:virology; D010942:Plant Viruses / Q000502:physiology*; D034622:RNA Interference; D012367:RNA, Viral / Q000235:genetics; D014026:Nicotiana / Q000235:genetics / Q000821:virology*; D059467:Transcriptome; D014779:Virus Replication
chemical_list: D012367:RNA, Viral