RESUMO
The complete nucleotide sequence of an Albanian isolate of grapevine leafroll-associated virus 7 (GLRaV-7-Alb) was determined. The viral genome consists of 16,404 nucleotides and has nine open reading frames (ORFs) that potentially encode proteins, most of which are typical for members of the family Closteroviridae. Only the 25-kDa (ORF8) and 27-kDa (ORF9) proteins had no apparent similarity to other viral proteins in the sequence databases. The genome structure of GLRaV-7-Alb closely resembles that of little cherry virus 1 and cordyline virus 1. In phylogenetic trees constructed with HSP70h sequences, these three viruses cluster together in a clade next to that comprising members of the genus Crinivirus, to which they are more closely related than to the clostero- and ampeloviruses. The molecular properties of these three viruses differ sufficiently from those of members of the three extant genera of the family Closteroviridae to warrant their classification in a novel genus.
Assuntos
Closteroviridae/classificação , Closteroviridae/isolamento & purificação , Genoma Viral , Doenças das Plantas/virologia , Vitis/virologia , Albânia , Closteroviridae/genética , Dados de Sequência Molecular , Fases de Leitura Aberta , FilogeniaRESUMO
Virus-resistant transgenic plants have been created primarily through the expression of viral sequences. It has been hypothesized that recombination between the viral transgene mRNA and the RNA of an infecting virus could generate novel viruses. As mRNA/viral RNA recombination can occur in virus-resistant transgenic plants, the key to testing this risk hypothesis is to compare the populations of recombinant viruses generated in transgenic and non-transgenic plants. This has been done with two cucumoviral systems, involving either two strains of cucumber mosaic virus (CMV), or CMV and the related tomato aspermy virus (TAV). Although the distribution of the sites of recombination in the CMV/CMV and TAV/CMV systems was quite different, equivalent populations of recombinant viruses were observed in both cases. These results constitute the first comparison of the populations of recombinants in transgenic and non-transgenic plants, and suggest that there is little risk of emergence of recombinant viruses in these plants, other than those that could emerge in non-transgenic plants.
Assuntos
Cucumovirus/genética , Genes Virais , Vírus de Plantas/genética , Plantas Geneticamente Modificadas/genética , Recombinação Genética , Sequência de Bases , Dados de Sequência Molecular , Plantas/genética , Plantas/virologia , Plantas Geneticamente Modificadas/virologia , Reprodutibilidade dos Testes , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Sensibilidade e EspecificidadeRESUMO
The genetic variability and population structure of a collection of 45 Grapevine leafroll-associated virus 3 (GLRaV-3) isolates were studied by single-stranded conformation polymorphism (SSCP) and sequence analysis of the RNA-dependent RNA polymerase (RdRp), heat-shock protein 70 homologue (HSP-70) and coat protein (CP) genes. The distribution of SSCP profiles was not correlated with the geographical origin of the isolates, indicating that GLRaV-3 is a single, undifferentiated population. The majority of the isolates showed an SSCP profile and a population structure that were composed of a single predominant variant. However, 10% of the isolates for the RdRp and HSP-70 genes and 15% for the CP gene were composed of a combination of two or more variants. Estimation of genetic diversity and phylogenetic analysis disclosed the possible existence of vines with mixed infections by diverging sequence variants, showing, in some cases, possible recombination events. Furthermore, differences in the genetic diversity and constraints existing in the three regions analysed indicated a higher variability in the CP gene. The epidemiological and biological implications of this finding are discussed.