Infection cycle of Artichoke Italian latent virus in tobacco plants: meristem invasion and recovery from disease symptoms

• Published in: PloS one Vol. 9; no. 6; p. e99446
• Main Authors: Santovito, Elisa, Mascia, Tiziana, Siddiqui, Shahid A, Minutillo, Serena Anna, Valkonen, Jari P T, Gallitelli, Donato
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 09.06.2014; Public Library of Science (PLoS)
• Subjects: Accumulation; Biology and Life Sciences; Colonization; Cynara scolymus; Flowers & plants; Gene expression; Gene Expression Profiling; Gene Expression Regulation, Plant; Gene Silencing; Genetic engineering; Health aspects; Host-Pathogen Interactions - genetics; Infection; Infections; Inoculation; Leaves; Life Cycle Stages; Medicine and Health Sciences; Meristem - virology; Nicotiana - genetics; Nicotiana - virology; Nicotiana benthamiana; Phenotype; Plant diseases; Plant Diseases - genetics; Plant Diseases - virology; Plant Leaves - virology; Plant viruses; Plant Viruses - physiology; Recovery; Recovery (Medical); Ribonucleic acid; RNA; RNA Interference; RNA polymerase; RNA, Viral - genetics; RNA-mediated interference; Tobacco; Tomatoes; Transcriptome; Transgenic plants; Viral infections; Virus Replication; Viruses; Italy
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0099446

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.