A highly divergent South African geminivirus species illuminates the ancient evolutionary history of this family.

Arvind Varsani,Aderito L Monjane,Edward P Rybicki,Dionne N Shepherd,Darren P Martin,Kyle Dent

doi:10.1186/1743-422x-6-36

Arvind Varsani, Aderito L Monjane + Show 4 more

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https://doi.org/10.1186/1743-422x-6-36

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Abstract

BackgroundWe have characterised a new highly divergent geminivirus species, Eragrostis curvula streak virus (ECSV), found infecting a hardy perennial South African wild grass. ECSV represents a new genus-level geminivirus lineage, and has a mixture of features normally associated with other specific geminivirus genera.ResultsWhereas the ECSV genome is predicted to express a replication associated protein (Rep) from an unspliced complementary strand transcript that is most similar to those of begomoviruses, curtoviruses and topocuviruses, its Rep also contains what is apparently a canonical retinoblastoma related protein interaction motif such as that found in mastreviruses. Similarly, while ECSV has the same unusual TAAGATTCC virion strand replication origin nonanucleotide found in another recently described divergent geminivirus, Beet curly top Iran virus (BCTIV), the rest of the transcription and replication origin is structurally more similar to those found in begomoviruses and curtoviruses than it is to those found in BCTIV and mastreviruses. ECSV also has what might be a homologue of the begomovirus transcription activator protein gene found in begomoviruses, a mastrevirus-like coat protein gene and two intergenic regions.ConclusionAlthough it superficially resembles a chimaera of geminiviruses from different genera, the ECSV genome is not obviously recombinant, implying that the features it shares with other geminiviruses are those that were probably present within the last common ancestor of these viruses. In addition to inferring how the ancestral geminivirus genome may have looked, we use the discovery of ECSV to refine various hypotheses regarding the recombinant origins of the major geminivirus lineages.

Highlights

We have characterised a new highly divergent geminivirus species, Eragrostis curvula streak virus (ECSV), found infecting a hardy perennial South African wild grass
Discovery of a highly divergent geminivirus lineage Six Eragrostis curvula plants presenting with streak symptoms similar to those encountered in maize streak virus (MSV) infected grasses [see Additional file 1] were sampled within 40 km of one another in the KwaZulu Natal province of South Africa between December 2007 and May 2008
BLASTx searches using the full genome nucleotide sequences of these isolates indicated significant (E score < 10-4), albeit low, identity matches to both mastrevirus cp [best match = Wheat dwarf virus (WDV)] and begomovirus rep [best match = Corchorus golden mosaic virus (CoGMV)] translated amino acid sequences

Summary

Introduction

We have characterised a new highly divergent geminivirus species, Eragrostis curvula streak virus (ECSV), found infecting a hardy perennial South African wild grass. Vector specificities, genome organizations and genome-wide sequence similarities, the family Geminiviridae is split into the Begomovirus, Curtovirus, Topocuvirus and Mastrevirus genera. The mastreviruses are both the most divergent and the most distinctive of the four divisions: whereas the begomoviruses, curtoviruses and topocuviruses share superficially similar genome structures (Figure 1) and are only known to naturally infect dicotyledonous plants, mastreviruses have unique genomic features and have been found infecting both monocotyledonous and dicotyledonous plants [3]. Positional homologues of transcription activator (trap or trap-like), replication enhancer (ren) and symptom determinant or silencing suppressor (C4) genes which share either undetectable or only very low degrees of sequence similarity across different genera are only found in the begomoviruses, topocuviruses and curtoviruses

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