RESUMEN
The nucleotide sequence and secondary structure of two representative variants from the Group III citrus viroids. CVd-IIIa (297 bases) and CVd-IIIb (294 bases) were determined. The variants are related to the apple scar skin viroid (ASSVd) family. Although smaller in size than any of the ASSVd-related viroids, the central conserved region as well as most of the terminal conserved region of ASSVd is retained. The rod-like structural configuration (characteristic of ASSVd) of the variants as predicted by minimum free energy analysis is presented.
Asunto(s)
Citrus/virología , ARN Viral/genética , Viroides/genética , Composición de Base , Secuencia de Bases , Secuencia Conservada , Frutas/virología , Datos de Secuencia Molecular , Conformación de Ácido Nucleico , Reacción en Cadena de la Polimerasa , ARN Viral/química , Análisis de Secuencia de ADN , Análisis de Secuencia de ARN , Homología de Secuencia de Ácido NucleicoRESUMEN
Infectivity of linear monomeric viroid RNA transcripts is known to be dependent on the site of cloning of the viroid and the viroid and vector sequences at the termini of the RNA transcripts. We report here the further characterization of cloning site and sequence requirements using 11 different monomeric cDNA constructs of citrus exocortis viroid; these differed from one another by the site of cloning and by nonviroid residues adjacent to the 5' and 3' termini of the viroid sequence in the RNA transcript. The infectivity of these transcripts was assayed by inoculation onto tomato seedlings; all infectious transcripts were wild type, indicating accurate processing. The basic requirement for infectivity appeared to be the ability of the RNA transcripts to form a short double-stranded region of viroid and vector sequences at the junction of the two termini. The site of cloning of the viroid RNA used for cloning was not important as cDNA clones prepared at seven sites provided infectious transcripts.
Asunto(s)
Virus de Plantas/patogenicidad , ARN Mensajero/toxicidad , ARN Viral/toxicidad , Viroides/patogenicidad , Composición de Base , Secuencia de Bases , Datos de Secuencia Molecular , Virus de Plantas/genética , ARN Mensajero/química , ARN Viral/química , Relación Estructura-Actividad , Viroides/genéticaRESUMEN
An unusual variant of citrus exocortis viroid (CEV) was detected when an inoculum source from Gynura aurantiaca D.C. was used to infect a hybrid tomato (Lycopersicon esculentum Mill. x L. peruvianum). The 92 nucleotide larger variant, CEV D-92, which displayed the characteristic circular and linear viroid structural forms, contained two repeated sequences spanning the V and T2 domains. A dramatic moderation of symptom expression in Gynura accompanied the incorporation of these repeated sequences. A comparison of the sequence and structure of CEV D-92 with coconut cadang-cadang viroid revealed similarities in the regions generating the naturally occurring terminal repeats suggesting a possible preferred site for RNA recombination between viroids.
Asunto(s)
Variación Genética/genética , Secuencias Repetitivas de Ácidos Nucleicos/genética , Viroides/genética , Secuencia de Bases , Datos de Secuencia Molecular , Plantas/microbiología , ARN Viral/aislamiento & purificación , Alineación de Secuencia , Análisis de Secuencia de ADN , Viroides/crecimiento & desarrolloRESUMEN
Isolates of citrus exocortis viroid (CEV) from a single sweet orange citrus source have been selected by sequential passage through the alternative hosts citron, Gynura aurantiaca, a hybrid tomato Lycopersicon esculentum x L. peruvianum, and from disorganized callus culture of the hybrid tomato. The distinctions in symptom expression, titre and electrophoretic mobility among the CEV isolates, operationally termed CEVc (citron), CEVg (Gynura), CEVt (tomato) and CEVcls (callus) are supported by characteristically different nucleotide sequences. The nucleotide sequence of full-length cDNA clones of CEVc purified from citron shows exchanges not reported for any previously described CEV variant. An unusual number of exchanges have been localized in the terminal domains of all the isolates analysed here. A common pattern of nucleotide exchanges, described as a 'tomato signature', can be detected in all of the isolates derived from hybrid tomato tissues.
Asunto(s)
Citrus/microbiología , Virus de Plantas/aislamiento & purificación , Viroides/aislamiento & purificación , Secuencia de Bases , Datos de Secuencia Molecular , Virus de Plantas/genética , ARN Viral/química , Especificidad de la Especie , Verduras/microbiología , Viroides/genética , Cultivo de VirusRESUMEN
The nucleotide sequences of 16 variants of the 247 nucleotide avocado sunblotch viroid (ASBV), purified from leaves of three avocado trees in separate locations, have been determined and compared with that of the previously published ASBV SB-1 sequence (Symons, R. H., Nucl. Acids Res. 9, 6527-6537, 1981). Most of the nucleotide differences were found to occur in the left- and right-hand loops of the ASBV molecule. The number of residues in the sequence variants varied from 246 to 251. Two sequence variants contained nucleotide changes in the double hammerhead-like self-cleaving structure identified in ASBV RNA. RNA transcripts of dimeric cDNA clones of these sequence variants retained their in vitro self-cleavage activity.