RESUMO
Citrus tristeza virus (CTV) strains were previously catalogued as seedling-yellows (SY) and non-SY (nSY) types, according to their yellowing and stunting effects on indicator seedlings. Among subisolates of the VT strain, which were selected from chronically infected Alemow plants, there was a correlation between the presence of 2.4-, 2.7- and 4.5-kb D-RNAs, and SY and nSY reactions, respectively. Similarly, plants infected with Mor-T subisolates, which cause SY, contained D-RNAs of 2.6 to 2.8 kb, while nSY subisolates from recovered sour orange tissue contained a major D-RNA of 5.1 kb. Plants harboring the 2.7-kb D-RNA were protected against challenge inoculation with a subisolate harboring the 4.5-kb D-RNA. This study suggests that the nSY reaction results either from the absence of SY gene(s) in the genomes of certain CTV strains or through the suppression of the effects of SY gene(s) by D-RNAs with 5' parts larger than 4000nt.
Assuntos
Citrus/virologia , Closterovirus/genética , Doenças das Plantas/virologia , Closterovirus/isolamento & purificação , Variação Genética , Genoma Viral , Hibridização de Ácido Nucleico , RNA de Cadeia Dupla/análise , RNA Viral/análise , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
The fusion sites between the termini of naturally occurring defective RNAs (D-RNAs) from three citrus tristeza virus (CTV) isolates were sequenced. Seven of eight clones showed a common 3' terminus of 940 nucleotides (nt) fused to 5' termini with different sizes. An extra cytosine nucleotide was found at the junction site of the majority of the common 3' D-RNAs. Molecular analysis of the plus and minus strands of the 0.9-kbp double-stranded RNA, corresponding to the CTV open reading frame 11 subgenomic RNA (sgRNA), showed that they were identical in length and sequence to the common 3' sequence of the D-RNAs. These results imply that viral sgRNA messengers also function as building components for genomic rearrangement and exchange of complete viral genes.
Assuntos
Citrus/virologia , Closterovirus/genética , Vírus Defeituosos/genética , Variação Genética , RNA Mensageiro , RNA Viral , Fusão Gênica Artificial , DNA Viral/análise , Genoma Viral , Reação em Cadeia da PolimeraseRESUMO
Groups of rabbits and young lambs were immunized subcutaneously and intramuscularly with a recombinant citrus tristeza virus (CTV) coat protein (rCTV-CP) antigen. Three weeks after primary immunization the animals were divided into two groups that were boosted either with rCTV-CP or with a partially purified preparation of CTV particles (ppCTV). Twelve and 15 days after the last injection, the animals were bled and the binding capacity of the antisera for CTV detection was examined for capture antibodies by the indirect ELISA. Considerably higher ELISA titers were obtained from animals that were boosted with ppCTV than with rCP. Boosting with partially purified native antigens after priming with recombinant antigens is expected to extend the applicability of the antisera for detecting other structural and non-structural viral antigens by trapping ELISA.
Assuntos
Anticorpos Antivirais/imunologia , Antígenos Virais/imunologia , Citrus/virologia , Closterovirus/imunologia , Ensaio de Imunoadsorção Enzimática/métodos , Animais , Anticorpos Antivirais/biossíntese , Anticorpos Antivirais/sangue , Antígenos Virais/genética , Capsídeo/genética , Capsídeo/imunologia , Galinhas , Closterovirus/genética , Closterovirus/isolamento & purificação , Imunização Secundária , Coelhos , Proteínas Recombinantes de Fusão , OvinosRESUMO
The complete, 19,226 nt sequence of the RNA genome from VT, a seedling yellows strain of citrus tristeza virus (CTV), was determined and found to have a genome organization identical with that of the previously determined CTV-T36 isolate, except that ORF 1 of CTV-VT was 70 nt shorter due to two widely separated 18 nt deletions. Sequence comparison of CTV-VT and CTV-T36 revealed approximately 89% identity throughout the ten 3' ORFs, but only 60-70% identity throughout ORF 1. The 5' nontranslated regions were only 60% identical whereas the 3' nontranslated regions were 97% identical. The transition between regions of similarity and deviation was gradual, suggesting that the sequence similarities and differences compared to CTV-T36 were unlikely to have arisen from a recent recombination event between a close T36 relative and a distantly related CTV isolate. This is the first attempt to compare in detail the variation between the genomes of two strains of a member of the closterovirus group. The observed deviation between the large RNA genomes of the two CTV strains is greater than that among different viruses of most other groups, raising the question of how to define the taxonomy of these viruses.
