RESUMO
RNA silencing mediated by small RNAs (sRNAs) is a conserved regulatory process with key antiviral and antimicrobial roles in eukaryotes. A widespread counter-defensive strategy of viruses against RNA silencing is to deploy viral suppressors of RNA silencing (VSRs), epitomized by the P19 protein of tombusviruses, which sequesters sRNAs and compromises their downstream action. Here, we provide evidence that specific Nicotiana species are able to sense and, in turn, antagonize the effects of P19 by activating a highly potent immune response that protects tissues against Tomato bushy stunt virus infection. This immunity is salicylate- and ethylene-dependent, and occurs without microscopic cell death, providing an example of "extreme resistance" (ER). We show that the capacity of P19 to bind sRNA, which is mandatory for its VSR function, is also necessary to induce ER, and that effects downstream of P19-sRNA complex formation are the likely determinants of the induced resistance. Accordingly, VSRs unrelated to P19 that also bind sRNA compromise the onset of P19-elicited defense, but do not alter a resistance phenotype conferred by a viral protein without VSR activity. These results show that plants have evolved specific responses against the damages incurred by VSRs to the cellular silencing machinery, a likely necessary step in the never-ending molecular arms race opposing pathogens to their hosts.
Assuntos
Resistência à Doença/fisiologia , Nicotiana/metabolismo , Interferência de RNA/fisiologia , RNA de Plantas/metabolismo , Tombusvirus/metabolismo , Proteínas Virais/metabolismo , Morte Celular/genética , Plantas Geneticamente Modificadas/genética , Plantas Geneticamente Modificadas/metabolismo , Plantas Geneticamente Modificadas/virologia , Ligação Proteica , RNA de Plantas/genética , Nicotiana/genética , Nicotiana/virologia , Tombusvirus/genética , Proteínas Virais/genéticaRESUMO
Conventional broad range RT-PCR and real time RT-PCR assays designed to detect human noroviruses (NoVs) also efficiently detect swine NoVs. Investigation of the primers and probe binding sites revealed strong homologies between swine NoVs genomic sequences and human primer sequences. These findings have a serious impact on food diagnostic methods and laboratories.
Assuntos
Infecções por Caliciviridae/diagnóstico , Contaminação de Alimentos/análise , Gastroenterite/diagnóstico , Norovirus/isolamento & purificação , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Animais , Sequência de Bases , Infecções por Caliciviridae/virologia , Primers do DNA , Microbiologia de Alimentos , Gastroenterite/virologia , Amplificação de Genes , Humanos , Norovirus/classificação , RNA Viral/análise , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Reação em Cadeia da Polimerase Via Transcriptase Reversa/normas , Sensibilidade e Especificidade , Alinhamento de Sequência , Homologia de Sequência do Ácido Nucleico , Especificidade da Espécie , SuínosRESUMO
This study reports the molecular characterization of novel caliciviruses, the St-Valérien-like viruses, which were isolated from pig feces in the province of Quebec, Canada between 2005 and 2007. The genomes of St-Valérien-like viruses contain 6409 nucleotides and include two main open reading frames (ORFs). ORF1 encodes the non structural (NS) polyprotein and the major capsid protein (VP1) while ORF2 encodes the putative basic minor capsid protein. Typical conserved amino acid motifs predict a gene order reminiscent of calicivirus genomes. Phylogenetic, pairwise homology, and distance analyses performed on complete genomic sequences and partial amino acid sequences from the NTPase, polymerase, and major capsid protein segregated the St-Valérien-like viruses in a unique cluster sharing a common root with the Tulane virus and the noroviruses. Based on the genomic analyses presented, the St-Valérien-like viruses are members of a new genus of Caliciviridae for which we propose the name Valovirus.
Assuntos
Infecções por Caliciviridae/veterinária , Caliciviridae/classificação , Caliciviridae/genética , Doenças dos Suínos/virologia , Animais , Caliciviridae/isolamento & purificação , Infecções por Caliciviridae/virologia , Análise por Conglomerados , Genoma Viral , Dados de Sequência Molecular , Fases de Leitura Aberta , Filogenia , Quebeque , RNA Viral/genética , Análise de Sequência de DNA , Homologia de Sequência , Suínos , Proteínas Virais/genéticaRESUMO
Noroviruses and sapoviruses are members of the family Caliciviridae and emerging enteric pathogens of humans and animals. Since their discovery and characterization in swine, relatively few strains have been described in detail. In order to investigate their genetic diversity, a total of 266 fecal samples collected in the province of Quebec, Canada, between 2005 and 2007 were screened for the presence of caliciviruses by RT-PCR using broadly reactive primers. Genetically heterogeneous caliciviruses were detected on the majority of farms. Typical noroviruses related to known swine genotypes were present on 20% of the farms. Sapoviruses were detected on 75% of the farms and were the most heterogeneous group. Further characterization of selected strains in their 3' end parts was carried out for their classification and unveiled possibly new clusters of sapoviruses. No human-like noroviruses or sapoviruses were detected in the present study.