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

Varsani A, Shepherd DN, Dent K, Monjane AL, Rybicki EP, Martin DP - Virol. J. (2009)

Bottom Line: ECSV represents a new genus-level geminivirus lineage, and has a mixture of features normally associated with other specific geminivirus genera.Whereas 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. arvind.varsani@uct.ac.za

ABSTRACT

Background: We 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.

Results: Whereas 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.

Conclusion: Although 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.

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The arrangement of genes and open reading frames (ORFs) within various major geminivirus lineages. BCTIV = beet curley top Iran virus. ECSV = Eragrostis curvula streak virus (reported for the first time in this paper). In the case of begomoviruses only the DNA-A/DNA-A-like genome component sequence is represented. Arrows indicate the positions and orientations of numbered ORFs (V = virion sense and C = complementary sense) that are known or strongly suspected to encode expressed proteins. mp = movement protein gene [4-7], cp = coat protein gene, rep = replication associated protein gene, ren = replication enhancer gene, trap = transcription activator protein gene, ss = silencing suppressor encoding ORF [8-14], sd = symptom determinant encoding ORF [15,16]; reg = potentially encoding a protein that regulates relative ssDNA and dsDNA concentrations [4]. A question mark indicates that an ORFs function is either completely unknown or only suspected. The only genes shared between all genomes are rep (in blue) and cp (in red). Variations in the presence or size of ORFs between members of the different geminivirus groups are indicated in grey. Intergenic regions are represented as open blocks and the probable hairpin structure at the origin of virion strand replication is indicated at the 12 o'clock position.
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Figure 1: The arrangement of genes and open reading frames (ORFs) within various major geminivirus lineages. BCTIV = beet curley top Iran virus. ECSV = Eragrostis curvula streak virus (reported for the first time in this paper). In the case of begomoviruses only the DNA-A/DNA-A-like genome component sequence is represented. Arrows indicate the positions and orientations of numbered ORFs (V = virion sense and C = complementary sense) that are known or strongly suspected to encode expressed proteins. mp = movement protein gene [4-7], cp = coat protein gene, rep = replication associated protein gene, ren = replication enhancer gene, trap = transcription activator protein gene, ss = silencing suppressor encoding ORF [8-14], sd = symptom determinant encoding ORF [15,16]; reg = potentially encoding a protein that regulates relative ssDNA and dsDNA concentrations [4]. A question mark indicates that an ORFs function is either completely unknown or only suspected. The only genes shared between all genomes are rep (in blue) and cp (in red). Variations in the presence or size of ORFs between members of the different geminivirus groups are indicated in grey. Intergenic regions are represented as open blocks and the probable hairpin structure at the origin of virion strand replication is indicated at the 12 o'clock position.

Mentions: Based on host ranges, 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].


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

Varsani A, Shepherd DN, Dent K, Monjane AL, Rybicki EP, Martin DP - Virol. J. (2009)

The arrangement of genes and open reading frames (ORFs) within various major geminivirus lineages. BCTIV = beet curley top Iran virus. ECSV = Eragrostis curvula streak virus (reported for the first time in this paper). In the case of begomoviruses only the DNA-A/DNA-A-like genome component sequence is represented. Arrows indicate the positions and orientations of numbered ORFs (V = virion sense and C = complementary sense) that are known or strongly suspected to encode expressed proteins. mp = movement protein gene [4-7], cp = coat protein gene, rep = replication associated protein gene, ren = replication enhancer gene, trap = transcription activator protein gene, ss = silencing suppressor encoding ORF [8-14], sd = symptom determinant encoding ORF [15,16]; reg = potentially encoding a protein that regulates relative ssDNA and dsDNA concentrations [4]. A question mark indicates that an ORFs function is either completely unknown or only suspected. The only genes shared between all genomes are rep (in blue) and cp (in red). Variations in the presence or size of ORFs between members of the different geminivirus groups are indicated in grey. Intergenic regions are represented as open blocks and the probable hairpin structure at the origin of virion strand replication is indicated at the 12 o'clock position.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2666655&req=5

Figure 1: The arrangement of genes and open reading frames (ORFs) within various major geminivirus lineages. BCTIV = beet curley top Iran virus. ECSV = Eragrostis curvula streak virus (reported for the first time in this paper). In the case of begomoviruses only the DNA-A/DNA-A-like genome component sequence is represented. Arrows indicate the positions and orientations of numbered ORFs (V = virion sense and C = complementary sense) that are known or strongly suspected to encode expressed proteins. mp = movement protein gene [4-7], cp = coat protein gene, rep = replication associated protein gene, ren = replication enhancer gene, trap = transcription activator protein gene, ss = silencing suppressor encoding ORF [8-14], sd = symptom determinant encoding ORF [15,16]; reg = potentially encoding a protein that regulates relative ssDNA and dsDNA concentrations [4]. A question mark indicates that an ORFs function is either completely unknown or only suspected. The only genes shared between all genomes are rep (in blue) and cp (in red). Variations in the presence or size of ORFs between members of the different geminivirus groups are indicated in grey. Intergenic regions are represented as open blocks and the probable hairpin structure at the origin of virion strand replication is indicated at the 12 o'clock position.
Mentions: Based on host ranges, 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].

Bottom Line: ECSV represents a new genus-level geminivirus lineage, and has a mixture of features normally associated with other specific geminivirus genera.Whereas 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.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand. arvind.varsani@uct.ac.za

ABSTRACT

Background: We 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.

Results: Whereas 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.

Conclusion: Although 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.

Show MeSH
Related in: MedlinePlus