Maintaining the structural integrity of the Bamboo mosaic virus 3' untranslated region is necessary for retaining the catalytic constant for minus-strand RNA synthesis

Role of an RNA pseudoknot involving the polyA tail in replication of Pepino mosaic potexvirus and related plant viruses

Pepino mosaic virus (PepMV) is a potexvirus of the family Alphaflexiviridae within the order of Tymovirales that threatens tomato production worldwide. PepMV possesses a positive-strand RNA genome with a 5′-methylguanosine cap and a 3′-polyA tail. Previously, using partially-purified viral RNA polymerase important secondary structures within the 3′-untranslated region (UTR) of PepMV RNA were identified. Here we show that an RNA pseudoknot can be formed in the 3′-UTR that includes part of the polyA tail. Using protoplasts, we demonstrate that the pseudoknot is required for replication of PepMV RNA. Mutational analysis and native gel electrophoresis further show that the pseudoknot is stabilized by UAU base triples, as is the human telomerase RNA pseudoknot. The presence of a pseudoknot in several other members of the Alpha- and Betaflexiviridae is supported by covariance analysis and native gel electrophoresis of other potexvirus, capillovirus and trichovirus RNAs. The ubiquitous presence of the pseudoknot in viruses of the Betaflexiviridae, suggests that the pseudoknot is a typical trait of the Betaflexiviridae that may have been adopted by many potexviruses during evolution.

First Report of Distinct Bamboo mosaic virus (BaMV) Isolates Infecting Bambusa funghomii in Vietnam and the Identification of a Highly Variable Region in the BaMV Genome

New isolates of the Bamboo mosaic virus (BaMV) were identified in Bambusa funghomii bamboo in Vietnam. Sequence analyses revealed that the Vietnam isolates are distinct from all known BaMV strains, sharing the highest sequence identities (about 77%) with the Yoshi isolates reported in California, USA. Unique satellite RNAs were also found to be associated with the BaMV Vietnam isolates. A possible recombination event was detected in the genome of BaMV-VN2. A highly variable region was identified in the ORF1 gene, in between the methyl transferase domain and helicase domain. These results revealed the presence of unique BaMV isolates in an additional bamboo species in one more country, Vietnam, and provided evidence in support of the possible involvement of environmental or host factors in the diversification and evolution of BaMV.

Genetic variability within the Polish tomato torrado virus Kra isolate caused by deletions in the 3'-untranslated region of genomic RNA1

Tomato torrado virus (ToTV) is in the genus Torradovirus in the family Secoviridae. ToTV contains a single-stranded, positive-sense, bipartite RNA genome encapsidated in icosahedral particles. It is a serious tomato pathogen causing significant crop reductions. Its occurrence has been reported from many countries worldwide. However, the state of knowledge of ToTV epidemiology, sequences and phylogeny is still rather poor. In this study we found that the Polish ToTV isolates are characterized by significant genetic variability of the 3'-untranslated region (UTR) of RNA1. The high resolution melting real-time PCR approach showed the presence of genetic variants within Polish ToTV isolates purified from Nicotiana benthamiana. Further sequencing of Kra ToTV revealed five genetic variants of RNA1 within the isolate differing in the 3'-untranslated region length resulting from deletions ranging from 6 to 163 nucleotides. In light of the published studies, the genetic variability of ToTV associated with large deletions within an isolate may not necessarily be rare and may influence the virus evolution and adaptation.