RESUMO

The newly discovered Citrus leprosis virus cytoplasmic type 2 (CiLV-C2) is one of the causal virus of citrus leprosis disease complex; which leads to substantial loss of citrus production in the states of Meta and Casanare of Colombia. Specific and sensitive detection methods are needed to monitor the dissemination of CiLV-C2 in Colombia, and to prevent introduction of CiLV-C2 to other citrus growing countries. Toward this end, putative coat protein gene (CPG) of CiLV-C2 was amplified from CiLV-C2 infected citrus tissues. The CPG was cloned, expressed and purified a recombinant coat protein of ∼31kDa which used to generate monoclonal antibodies and polyclonal antisera. Four monoclonal antibodies and two polyclonal antisera were selected as being specific following Western blotting. The monoclonal antibody MAb E5 and polyclonal antiserum PAb UF715 were selected testing with an extract of CiLV-C2 infected leaves using triple antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA). In addition, an immunocapture RT-PCR was standardized using MAb E5 for specific and sensitive detection of CiLV-C2. The standardized TAS-ELISA and IC-RT-PCR were able to detect CiLV-C2 in the extracts of symptomatic citrus leprosis tissues up to the dilutions of 1:160 and 1:2580, respectively. Result demonstrated that CiLV-C2 is present in citrus orchards in Meta and Casanare citrus growing areas of Colombia. TAS-ELISA could be used for routine detection of CiLV-C2, epidemiological studies, and for border inspections for quarantine purposes. IC-RT-PCR could be valuable for CiLV-C2 validation and viral genome analysis.

Assuntos

Citrus/virologia , Ensaio de Imunoadsorção Enzimática/métodos , Doenças das Plantas/virologia , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Rhabdoviridae/isolamento & purificação , Colômbia , Rhabdoviridae/imunologia , Sensibilidade e Especificidade

RESUMO

Citrus leprosis virus C (CiLV-C), a causal agent of the leprosis disease in citrus, is mostly present in the South and Central America and spreading toward the North America. To enable better diagnosis and inhibit the further spread of this re-emerging virus a quantitative (q) real-time reverse transcription polymerase chain reaction (qRT-PCR) assay is needed for early detection of CiLV-C when the virus is present in low titer in citrus leprosis samples. Using the genomic sequence of CiLV-C, specific primers and probe were designed and synthesized to amplify a 73 nt amplicon from the movement protein (MP) gene. A standard curve of the 73 nt amplicon MP gene was developed using known 10(10)-10(1) copies of in vitro synthesized RNA transcript to estimate the copy number of RNA transcript in the citrus leprosis samples. The one-step qRT-PCR detection assays for CiLV-C were determined to be 1000 times more sensitive when compared to the one-step conventional reverse transcription polymerase chain reaction (RT-PCR) CiLV-C detection method. To evaluate the quality of the total RNA extracts, NADH dehydrogenase gene specific primers (nad5) and probe were included in reactions as an internal control. The one-step qRT-PCR specificity was successfully validated by testing for the presence of CiLV-C in the total RNA extracts of the citrus leprosis samples collected from Belize, Costa Rica, Mexico and Panama. Implementation of the one-step qRT-PCR assays for CiLV-C diagnosis should assist regulatory agencies in surveillance activities to monitor the distribution pattern of CiLV-C in countries where it is present and to prevent further dissemination into citrus growing countries where there is no report of CiLV-C presence.

Assuntos

Citrus/virologia , Doenças das Plantas/virologia , Vírus de Plantas/isolamento & purificação , Vírus de RNA/isolamento & purificação , Reação em Cadeia da Polimerase em Tempo Real/métodos , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , América Central , Primers do DNA/genética , Sondas de Oligonucleotídeos/genética , Proteínas do Movimento Viral em Plantas/genética , Reação em Cadeia da Polimerase em Tempo Real/normas , Padrões de Referência , Reação em Cadeia da Polimerase Via Transcriptase Reversa/normas , Sensibilidade e Especificidade

RESUMO

Citrus leprosis in Colombia was previously shown to be caused by cytoplasmic Citrus leprosis virus (CiLV-C). In 2011, enzyme-linked immunosorbent assay and reverse-transcription polymerase chain reaction (RT-PCR)-based diagnostic methods failed to identify CiLV-C from citrus samples with symptoms similar to citrus leprosis; however, virions similar to CiLV-C were observed in the cytoplasm of the symptomatic leaves by transmission electron microscopy. Furthermore, the causal organism was transmitted by the false spider mite, Brevipalpus phoenicis, to healthy citrus seedlings. A library of small RNAs was constructed from symptomatic leaves and used as the template for Illumina high-throughput parallel sequencing. The complete genome sequence and structure of a new bipartite RNA virus was determined. RNA1 (8,717 nucleotides [nt]) contained two open reading frames (ORFs). ORF1 encoded the replication module, consisting of five domains: namely, methyltransferase (MTR), cysteine protease-like, FtsJ-MTR, helicase (Hel), and RNA-dependent RNA polymerase (RdRp); whereas ORF2 encoded the putative coat protein. RNA2 (4,989 nt) contained five ORFs that encode the movement protein (MP) and four hypothetical proteins (p7, p15, p24, and p61). The structure of this virus genome resembled that of CiLV-C except that it contained a long 3' untranslated terminal region and an extra ORF (p7) in RNA2. Both the RNA1 and RNA2 of the new virus had only 58 and 50% nucleotide identities, respectively, with known CiLV-C sequences and, thus, it appears to be a novel virus infecting citrus. Phylogenetic analyses of the MTR, Hel, RdRp, and MP domains also indicated that the new virus was closely related to CiLV-C. We suggest that the virus be called Citrus leprosis virus cytoplasmic type 2 (CiLV-C2) and it should be unambiguously classified as a definitive member of the genus Cilevirus. A pair of CiLV-C2 genome-specific RT-PCR primers was designed and validated to detect its presence in citrus leprosis samples collected from the Casanare and Meta states in Colombia.

Assuntos

Vetores Aracnídeos/virologia , Citrus/virologia , Ácaros/virologia , Doenças das Plantas/virologia , Vírus de RNA/isolamento & purificação , Sequência de Aminoácidos , Animais , Citrus/ultraestrutura , Colômbia , Frutas , Biblioteca Gênica , Genoma Viral/genética , Sequenciamento de Nucleotídeos em Larga Escala , Microscopia Eletrônica de Transmissão , Dados de Sequência Molecular , Filogenia , Folhas de Planta/virologia , Vírus de RNA/classificação , Vírus de RNA/genética , RNA Viral/genética , RNA Polimerase Dependente de RNA/genética , Plântula/ultraestrutura , Plântula/virologia , Alinhamento de Sequência , Análise de Sequência de DNA

RESUMO

In September 1998, tomato plants in Barbados exhibited symptoms of severe leaf curling without marginal chlorosis. These symptoms were often associated with an increase in whitefly (Bemisia tabaci) populations. DNA was extracted from leaf tissue from symptomatic tomato plants. Polymerase chain reaction (PCR) was performed with DNA-A degenerate primer pair PAC1v1978/PAV1c715, which amplifies part of the rep gene, the cp gene, and the common region (CR), and with DNA-B primer pair PBC1v2039/PBV1c800, which amplifies part of the bc1 and bv1 genes and the CR (2). The amplified PCR fragments of DNA-A and DNA-B were 1.3 and 1.4 kb, respectively, which are the expected sizes from bipartite, whitefly-transmitted geminiviruses of the Western Hemisphere (2). DNA sequence of the cloned fragments of DNA-A and DNA-B are available as GenBank No. AF213013 and AF213014, respectively. The 181 nucleotides of the CR of DNA-A had a nucleotide identity of 96% with the CR of DNA-B, which indicates that this is a bipartite begomovirus. Pairwise comparisons using DNASTAR (DNASTAR, Madison, WI) of the sequenced part of DNA-A was most similar to Cabbage leaf curl virus (CaLCuV, 69%, U65529) and Squash leaf curl virus extended host range isolate (SqLCV-E, 64%, M38183), and <59% to 13 other bipartite Western Hemisphere geminiviruses and Tomato yellow leaf curl virus from Israel (X15656). Pairwise comparisons of the DNA-B fragment sequence was 59 and 55% similar to CaLCuV (U65530) and SqLCV-E (M38182), respectively. Phylogenetic analysis of DNA-A of the major groups of Western Hemisphere begomoviruses placed the Barbados tomato-infecting geminivirus in the cluster with CaLCuV and SqLCV-E (1), while DNA-B analysis placed it with CaLCuV. The DNA-A amplified fragment was used as a probe at high stringency with the dot blot hybridization assay using the Genius II labeling and detection kit (Boeringer Mannheim) to detect this geminivirus in tomato and several other plant species, which had typical geminiviral symptoms. Strong hybridization signals were obtained for all 23 tomato plants with symptoms, weak signals were observed for two of three muskmelon and two of seven watermelon plants, all with leaf curling symptoms. No hybridization signals were observed for peppers with leaf curling symptoms and two weed species, Macroptilium lathyroides and Rhynchosia minima, with golden mosaic symptoms or with the symptomless plant species used as negative controls. The weak signals observed from watermelon and muskmelon samples indicated the presence of low virus titer or geminiviruses distinct from this tomato virus. The presence of viral DNA in these two plant species was confirmed by PCR with degenerate primers described above. Resulting database searches of sequences in the GenBank revealed that the Barbados tomato virus appears to be a previously unreported virus. This new virus is given the provisional name Tomato leaf curl Barbados virus (ToLCBBV). References: (1) J. C. Faria et al. Phytopathology 84:321, 1994. (2) M. R. Rojas et al. Plant Dis. 77:340, 1993.

RESUMO

Rhynchosia minima was suspected to be a weed host of Bean golden yellow mosaic virus (BGYMV, previously designated Bean golden mosaic virus type II). Leaf tissue that exhibited yellow mosaic foliar symptoms characteristic of a geminivirus infection was collected in the Comayagua Valley in Honduras in July 1999. Extraction of viral DNA from the symptomatic leaves was accomplished with the DNeasy Plant Mini Kit (Qiagen Inc., Valencia, CA). Subsequent viral DNA amplification was accomplished with degenerative primers for the cp gene (AV494/AC1048) (4). The 570-bp fragment was cloned into the pGEM T-Easy vector (Promega Corp., Madison, WI) producing the recombinant plasmid pRhyb5. The viral insert was sequenced, and from this sequence, specific primers (RHc549 and RHv29) were designed to amplify the remaining part of DNA-A. The 2.1-kb-amplified polymerase chain reaction (PCR) fragment was cloned into the pGEM T-Easy vector producing the recombinant plasmid (pRhya-sp), and the viral insert was sequenced. Nucleotide sequence comparison (GAP program, Wisconsin Package Version 10.0, Genetics Computer Group, Madison, WI) of the complete 2,624-bp DNA-A (GenBank accession no. AF239671) to geminiviruses representing the major phylogenetic clusters (1) showed nucleotide identities ranging from 63 to 82%. Sequence comparisons for the common region and rep, trap, ren, and cp genes with the most closely related geminivirus, Pepper hausteco virus (PHV, X70418), gave 76, 82, 79, 81, and 82% nucleotide identities, respectively. There is a direct repeat (TATCGGT) of 7 nt 5' (viral sense polarity) of the conserved TATA box, and this repeat is most analogous to that in PHV (1). Specific primers were designed in the complementary sense (RGBc2414, BGBc2553) from the common region DNA-A sequence and used with a degenerative viral sense primer for the DNA-B (PBC1v2039) (3) to amplify a 647-bp fragment. Sequence comparison for the common region (134 nt from the rep gene start codon toward the 3' end) from the DNA-B sequence had 88% nt identity to the DNA-A sequence, thus indicating that this geminivirus is bipartite. These sequence analyses indicated that this geminivirus isolated from R. minima is distinct from previously described geminiviruses, and we propose the name Rhynchosia golden mosaic virus (RGMV). From rep gene sequence alignments, RGMV has an apparent genome recombination between Old and New World geminiviruses (Tomato yellow leaf curl virus and Bean dwarf mosaic virus) as previously noted for PHV (2). Our results indicate that RGMV is a distinct geminivirus from BGYMV, and, thus, additional studies are needed to establish the importance of R. minima as a reservoir for vegetable-infecting geminiviruses. This study is the first report of another virus in the PHV phylogenetic cluster and is thus of importance in the understanding of recombinant viruses and their phylogenetic relationship to other characterized geminiviruses. References: (1) J. C. Faria et al. Phytopathology 84:321, 1994. (2) M. Padidam et al. Virology 265:218, 1999. (3) M. R. Rojas et al. Plant Dis. 77:340, 1993. (4) S. Wyatt and J. K. Brown. Phytopathology 86:1288, 1996.