RESUMEN
Agrobacterium rhizogenes and Agrobacterium tumefaciens are plant pathogenic bacteria capable of transferring DNA fragments [transfer DNA (T-DNA)] bearing functional genes into the host plant genome. This naturally occurring mechanism has been adapted by plant biotechnologists to develop genetically modified crops that today are grown on more than 10% of the world's arable land, although their use can result in considerable controversy. While assembling small interfering RNAs, or siRNAs, of sweet potato plants for metagenomic analysis, sequences homologous to T-DNA sequences from Agrobacterium spp. were discovered. Simple and quantitative PCR, Southern blotting, genome walking, and bacterial artificial chromosome library screening and sequencing unambiguously demonstrated that two different T-DNA regions (IbT-DNA1 and IbT-DNA2) are present in the cultivated sweet potato (Ipomoea batatas [L.] Lam.) genome and that these foreign genes are expressed at detectable levels in different tissues of the sweet potato plant. IbT-DNA1 was found to contain four open reading frames (ORFs) homologous to the tryptophan-2-monooxygenase (iaaM), indole-3-acetamide hydrolase (iaaH), C-protein (C-prot), and agrocinopine synthase (Acs) genes of Agrobacterium spp. IbT-DNA1 was detected in all 291 cultigens examined, but not in close wild relatives. IbT-DNA2 contained at least five ORFs with significant homology to the ORF14, ORF17n, rooting locus (Rol)B/RolC, ORF13, and ORF18/ORF17n genes of A. rhizogenes. IbT-DNA2 was detected in 45 of 217 genotypes that included both cultivated and wild species. Our finding, that sweet potato is naturally transgenic while being a widely and traditionally consumed food crop, could affect the current consumer distrust of the safety of transgenic food crops.
Asunto(s)
Agrobacterium/genética , Genoma de Planta , Ipomoea batatas/genética , Plantas Modificadas Genéticamente , ADN Bacteriano/genética , ADN de Plantas/genética , Inocuidad de los Alimentos , Transferencia de Gen Horizontal , Sistemas de Lectura Abierta , Filogenia , Hojas de la Planta/metabolismo , Raíces de Plantas/metabolismo , Brotes de la Planta/metabolismo , Tallos de la Planta/metabolismo , ARN Interferente Pequeño/genética , Análisis de Secuencia de ADNRESUMEN
The complete nucleotide sequence of the isolate C1 of Sweet potato feathery mottle virus (SPFMV) strain C and the 5' region of several other strains were determined and analyzed together with the sequences of isolates representing the EA, RC and O strains. This provided molecular evidence for the reclassification of SPFMV strains into two species and the occurrence of a complex recombinant isolate. Analysis also revealed a hypervariable domain in the P1 protein, which separates an N-terminal region unique to SPFMV and members of the ipomovirus species Sweet potato mild mottle virus from the C-terminal protease domain, which is conserved among all potyviruses.
Asunto(s)
Ipomoea batatas/virología , Enfermedades de las Plantas/virología , Potyvirus/clasificación , Potyvirus/genética , Regiones no Traducidas 5' , Análisis por Conglomerados , Genoma Viral , Datos de Secuencia Molecular , Filogenia , Potyvirus/aislamiento & purificación , Estructura Terciaria de Proteína , ARN Viral/genética , Alineación de Secuencia , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Proteínas Virales/genéticaRESUMEN
We report the first identification of novel viruses, and sequence of an entire viral genome, by a single step of high-throughput parallel sequencing of small RNAs from diseased, as well as symptomless plants. Contigs were assembled from sequenced total siRNA from plants using small sequence assembly software and could positively identify RNA, ssDNA and dsDNA reverse transcribing viruses and in one case spanned the entire genome. The results present a novel approach which cannot only identify known viral pathogens, occurring at extremely low titers, but also novel viruses, without the necessity of any prior knowledge.