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BMC Evol Biol. 2009 May 21;9:112. doi: 10.1186/1471-2148-9-112.

Geminiviruses: a tale of a plasmid becoming a virus.

Author information

1
Department of Biological and Environmental Sciences and Institute of Biotechnology, Biocenter 2, PO Box 56 (Viikinkaari 5), FIN-00014 University of Helsinki, Helsinki, Finland. mart.krupovic@helsinki.fi

Abstract

BACKGROUND:

Geminiviruses (family Geminiviridae) are small single-stranded (ss) DNA viruses infecting plants. Their virion morphology is unique in the known viral world - two incomplete T = 1 icosahedra are joined together to form twinned particles. Geminiviruses utilize a rolling-circle mode to replicate their genomes. A limited sequence similarity between the three conserved motifs of the rolling-circle replication initiation proteins (RCR Reps) of geminiviruses and plasmids of Gram-positive bacteria allowed Koonin and Ilyina to propose that geminiviruses descend from bacterial replicons.

RESULTS:

Phylogenetic and clustering analyses of various RCR Reps suggest that Rep proteins of geminiviruses share a most recent common ancestor with Reps encoded on plasmids of phytoplasmas, parasitic wall-less bacteria replicating both in plant and insect cells and therefore occupying a common ecological niche with geminiviruses. Capsid protein of Satellite tobacco necrosis virus was found to be the best template for homology-based structural modeling of the geminiviral capsid protein. Good stereochemical quality of the generated models indicates that the geminiviral capsid protein shares the same structural fold, the viral jelly-roll, with the vast majority of icosahedral plant-infecting ssRNA viruses.

CONCLUSION:

We propose a plasmid-to-virus transition scenario, where a phytoplasmal plasmid acquired a capsid-coding gene from a plant RNA virus to give rise to the ancestor of geminiviruses.

PMID:
19460138
PMCID:
PMC2702318
DOI:
10.1186/1471-2148-9-112
[Indexed for MEDLINE]
Free PMC Article

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