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Revisiting the roles of replicase complex proteins in tobamovirus replication and suppression of RNA silencing

Nachelli Malpica López, Hortensia. Revisiting the roles of replicase complex proteins in tobamovirus replication and suppression of RNA silencing. 2017, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_12389

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Abstract

Tobamoviral replicase possesses an RNA-dependent RNA polymerase (RDR) domain and is translated from genomic (g)RNA via a stop codon readthrough mechanism at a one-to-ten ratio relative to a shorter protein lacking the RDR domain. The two proteins share methyltransferase and helicase domains and form a heterodimer implicated in gRNA replication. The shorter protein is also implicated in suppressing RNA silencing based antiviral defenses. Using a stop codon mutant of Oilseed rape mosaic tobamovirus (ORMV), we demonstrate that the readthrough replicase (p182) is sufficient for gRNA replication and for subgenomic RNA transcription during systemic infection in Nicotiana benthamiana and Arabidopsis thaliana. However, the mutant virus displays milder symptoms and does not interfere with HEN1-mediated methylation of viral short interfering (si)RNAs or plant small (s)RNAs. The mutant virus tends to revert the stop codon, thereby restoring expression of the shorter protein (p125), even in the absence of plant Dicer-like activities that generate viral siRNAs. Plant RDR activities that generate endogenous siRNA precursors do not prevent replication or movement of the mutant virus, and double-stranded precursors of viral siRNAs representing the entire virus genome are likely synthesized by p182. Transgenic expression of p125 partially recapitulates the ORMV disease symptoms associated with overaccumulation of plant sRNAs. Taken together, the readthrough replicase p182 is sufficient for viral replication and transcription but not for silencing suppression. By contrast, the shorter p125 protein suppresses silencing, provokes severe disease symptoms, causes overaccumulation of unmethylated viral and plant sRNAs but it is not an essential component of the viral replicase complex.
Advisors:Boller, Thomas and Pooggin, Mikhail M. and Blevins, Todd
Faculties and Departments:05 Faculty of Science > Departement Umweltwissenschaften > Botanik > Pflanzenphysiologie Pathogenabwehr (Boller)
UniBasel Contributors:Boller, Thomas
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:12389
Thesis status:Complete
Bibsysno:Link to catalogue
Number of Pages:1 Online-Ressource (vii, 127 Blätter)
Language:English
Identification Number:
Last Modified:22 Jan 2018 15:53
Deposited On:13 Dec 2017 12:49

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