Distinct circular single-stranded DNA viruses exist in different soil types.

The potential dependence of virus populations on soil types was examined by electron microscopy, and the total abundance of virus particles in four soil types was similar to that previously observed in soil samples. The four soil types examined differed in the relative abundances of four morphological groups of viruses. Machair, a unique type of coastal soil in western Scotland and Ireland, differed from the others tested in having a higher proportion of tailed bacteriophages.

Novel bacteriophages containing a genome of another bacteriophage within their genomes.

A novel bacteriophage infecting Staphylococus pasteuri was isolated during a screen for phages in Antarctic soils. The phage named SpaA1 is morphologically similar to phages of the family Siphoviridae. The 42,784 bp genome of SpaA1 is a linear, double-stranded DNA molecule with 3' protruding cohesive ends.

Resistance of transgenic tobacco plants incorporating the putative 57-kDa polymerase read-through gene of Tobacco rattle virus against rub-inoculated and nematode-transmitted virus.

Nicotiana tabacum plants were transformed with the 57-kDa read-through domain of the replicase gene of Tobacco rattle virus (TRV) isolate SYM. From a total of six lines containing the viral transgene, four displayed various levels of resistance to TRV infection. Transgenic plants from line 81G were highly resistant to foliar rub-inoculation with the homologous isolate, or with isolates TRV-PpK20 and TRV-PLB, which are almost identical to TRV-SYM in RNA1 sequence.

Caspase-resistant VirD2 protein provides enhanced gene delivery and expression in plants.

Agrobacterium tumefaciens VirD2 protein is one of the key elements of Agrobacterium-mediated plant transformation, a process of transfer of T-DNA sequence from the Agrobacterium tumour inducing plasmid into the nucleus of infected plant cells and its integration into the host genome. The VirD2 protein has been shown to be a substrate for a plant caspase-like protease activity (PCLP) in tobacco. We demonstrate here that mutagenesis of the VirD2 protein to prevent cleavage by PCLP increases the efficiency of reporter gene transfer and expression.

Heterologous expression of plant virus genes that suppress post-transcriptional gene silencing results in suppression of RNA interference in Drosophila cells.

Background: RNA interference (RNAi) in animals and post-transcriptional gene silencing (PTGS) in plants are related phenomena whose functions include the developmental regulation of gene expression and protection from transposable elements and viruses. Plant viruses respond by expressing suppressor proteins that interfere with the PTGS system.

Results: Here we demonstrate that both transient and constitutive expression of the Tobacco etch virus HC-Pro silencing suppressor protein, which inhibits the maintenance of PTGS in plants, prevents dsRNA-induced RNAi of a lacZ gene in cultured Drosophila cells.

Functional replacement of the tobacco rattle virus cysteine-rich protein by pathogenicity proteins from unrelated plant viruses.

Mutation of the 16K gene encoded by RNA1 of Tobacco rattle virus (TRV) greatly reduced the levels of viral RNA that accumulated in both infected protoplasts and plants, showing that the 16K cysteine-rich protein (CRP) is required for efficient multiplication of TRV. Overexpression of the 16K protein, either from an additional copy of the gene carried on TRV RNA2 or from a PVX vector, led to an increase in the severity of disease symptoms, suggesting that the protein has a role in the pathogenicity of the virus. Mutation of the 16K gene could be overcome by expression from RNA2 of the Cucumber mosaic virus 2b gene, the Soil-borne wheat mosaic virus 19K gene, or the Barley stripe mosaic virus gammab gene, indicating that the proteins encoded by these diverse genes may have similar functions.

A naturally occurring deleted form of RNA 2 of Potato mop-top virus.

A spontaneous deletion in RNA 2 of Potato mop-top virus (PMTV) was identified by RT-PCR. The deletion occurred reproducibly during manual passage of two isolates of PMTV and during fungal inoculation of plants with viruliferous soil. The borders of the deletion were conserved in all instances and sequence analyses showed that a contiguous segment of 2113 nucleotides was deleted internally from the genomic RNA 2, leaving the 5'- and 3'-terminal sequences.