Geminiviruses: a tale of a plasmid becoming a virus

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


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Bayes Theorem
  • Capsid Proteins / genetics*
  • Cluster Analysis
  • Evolution, Molecular*
  • Geminiviridae / genetics*
  • Genes, Viral
  • Genome, Viral
  • Likelihood Functions
  • Models, Molecular
  • Molecular Sequence Data
  • Phylogeny
  • Phytoplasma / genetics
  • Plasmids
  • Protein Structure, Secondary
  • Replicon*
  • Sequence Alignment


  • Capsid Proteins