Sequence and identification of the barley yellow dwarf virus coat protein gene

Improvement of Barley yellow dwarf virus-PAV detection in single aphids using a fluorescent real time RT-PCR

One of the major factors determining the incidence of Barley yellow dwarf virus (BYDV) on autumn-sown cereals is the viruliferous state of immigrant winged aphids. This variable is assessed routinely using the enzyme-linked immunosorbant assay (ELISA). However, the threshold for virus detection by ELISA can lead to false negative results for aphids carrying less than 10(6) particles. Although molecular detection techniques enabling the detection of lower virus quantities in samples are available, the relatively laborious sample preparation and data analysis have restricted their use in routine applications. A gel-free real-time one-step reverse transcription polymerase chain reaction (RT-PCR) protocol is described for specific detection and quantitation of BYDV-PAV, the most widespread BYDV species in Western Europe. This new assay, based on TaqMan technology, detects and quantifies from 10(2) to 10(8) BYDV-PAV RNA copies. This test is 10 and 10(3) times more sensitive than the standard RT-PCR and ELISA assays published previously for BYDV-PAV detection and significantly improves virus detection in single aphids. Extraction of nucleic acids from aphids using either phenol/chloroform or chelatin resin-based protocols allow the use of pooled samples or of a small part (up to 1/1600th) of a single aphid extract for efficient BYDV-PAV detection.

Biolistic-mediated inoculation of immature wheat embryos with Barley yellow dwarf virus-PAV

Successful mechanical inoculation of plant with viruses requires an efficient method to introduce the viral pathogen into the appropriate cells of the plant. Barley yellow dwarf virus-PAV (BYDV-PAV, Luteovirus), transmitted naturally by aphids, must be inoculated into the phloem tissue to infect systemically inoculated hosts. The particle bombardment method used widely for nucleic acid transfer into plant tissues was adapted to inoculate immature embryos of winter and spring wheat cultivars with either BYDV-PAV particles or viral full-length RNAs. DAS-ELISA and RT-PCR were carried out on extracts of developed leaves at 7 weeks post-bombardment and revealed that up to 14% of bombarded embryos produced BYDV-infected wheat plants. This is the first report of an aphid-free inoculation method for BYDV.

In Situ Localization of Barley Yellow Dwarf Virus-PAV 17-kDa Protein and Nucleic Acids in Oats

ABSTRACT Barley yellow dwarf virus strain PAV (BYDV-PAV) RNA and the 17-kDa protein were localized in BYDV-PAV-infected oat cells using in situ hybridization and in situ immunolocalization assays, respectively. The in situ hybridization assay showed labeling of filamentous material in the nucleus, cytoplasm, and virus-induced vesicles with both sense and antisense nucleic acid probes, suggesting that the filamentous material found in BYDV-PAV-infected cells contains viral RNA. BYDV-PAV negative-strand RNA was detected before virus particles were observed, which indicates that RNA replication is initiated before synthesis of viral coat protein in the cytoplasm. The 17-kDa protein was associated with filamentous material in the cytoplasm, nucleus, and virus-induced vesicles. The labeling densities observed using antibodies against the 17-kDa protein were similar in the nucleus and cytoplasm. No labeling of the 17-kDa protein was observed in plasmodesmata, but filaments in the nuclear pores occasionally were labeled. Since BYDV-PAV RNA and 17-kDa protein colocalized within infected cells, it is possible that single-stranded viral RNA is always associated with the 17-kDa protein in vivo. The 17-kDa protein may be required for viral nucleic acid filaments to traverse the nuclear membrane or other membrane systems.

Barley yellow dwarf viruses

Barley yellow dwarf viruses represent one of the most economically important and ubiquitous groups of plant viruses. This review focuses primarily on four research areas in which progress has been most rapid. These include (a) evidence supporting reclassification of BYDVs into two genera; (b) elucidation of gene function and novel mechanisms controlling gene expression; (c) initial forays into understanding the complex interactions between BYDV virions and their aphid vectors; and (d) replication of a BYDV satellite RNA. Economic losses, symptomatology, and means of control of BYD are also discussed.

Molecular cloning and nucleotide sequence of the coat protein gene of a Cuban isolate of potato leafroll virus and its expression in Escherichia coli

Total RNA from infected Physalis floridana was isolated to generate complementary DNA corresponding to the coat protein (GP) gene of a Cuban isolate of potato leaf roll virus (PLRV). This cDNA was amplified by the polymerase chain reaction (PCR) and cloned into the bacterial expression vectors pEX(1-3) for fusion protein expression in E. coli. The product was detected by antibodies specific for the PLRV CP. The coding sequence of the CP gene was determined, and the predicted length of the CP was 208 amino acids (23 kD). The nucleotide sequences and deduced amino acid sequences were compared with the other PLRV isolates and found to be 97-99.5% identical at both the nucleotide and amino acid sequence level of other isolates. Comparison of the deduced amino acid sequences of the PLRVcub CP revealed considerable homology to other luteoviruses. We believe that the protocol described could be applicable to other plant viruses of low abundance or of cumbersome isolation, since this method is less time consuming than the traditional methods of cloning coat protein genes of plant viruses with known sequences.

Nucleotide sequence of a circular single-stranded DNA associated with coconut foliar decay virus

A circular single-stranded (ss) covalently closed (ccc) DNA associated with coconut foliar decay virus (CFDV) was purified, amplified by the polymerase chain reaction, and subcloned and its sequence established by analysis of overlapping subgenomic cDNA clones. The complete CFDV sequence comprised 1291 nucleotides and contained open reading frames for six proteins of molecular weight larger than 5 kDa. One of these (ORF1, 33.4 kDa) codes for a leucine-rich protein with the nucleoside triphosphate-binding motif GXGKS and may possibly participate in virus replication. The putative viral protein encoded by ORF3 (6.4 kDa) is a positively charged arginine-rich protein with homology to the capsid protein of nuclear polyhedrosis virus, and may represent the CFDV coat protein. CFDV DNA can form a stable stem structure of 10 GC base pairs subtending a loop sequence which in one orientation closely resembles the motif TAATATTAC conserved in a similar structural arrangement within the geminivirus group. Otherwise no sequence homology to DNA-containing plant viruses of the gemini- or caulimovirus groups was found. CFDV therefore represents a new taxonomic group of plant viruses.

Cloning of the gene for the capsid protein of potato leafroll virus

DNA complementary to the RNA of purified potato leafroll virus (PLRV) was synthesized and cloned into the lambda insertion vector NM1149. Overlapping PLRV-specific cDNA clones were isolated that represent some 80% of the viral genome. Sequences coding for the capsid protein were identified by subcloning size-selected cDNAs into the lambda expression vector gt11 and screening with PLRV-specific antisera. The gene for the viral capsid protein was shown to reside in the 3' terminal half of the genomic RNA. Sequence comparisons with the recently published genomes of the beet western yellows virus (BWYV) and the barely yellow dwarf virus (BYDV) reveal some 65% protein sequence homology between the capsid proteins of BWYV and PLRV and some 45% homology between BYDV and PLRV. Furthermore, it is evident that the structural organization of the PLRV genome in the CP gene region is similar to that of BWYV and BYDV.

Nucleotide sequence and organization of potato leafroll virus genomic RNA

The nucleotide sequence of the genomic RNA of potato leafroll virus was determined and its genetic organization deduced. The RNA is 5882 nucleotides long and contains 6 open reading frames (ORFs) encoding proteins of 70, 70, 56, 28, 23 and 17 kDa. The putative genes for the coat protein (23 kDa) and the RNA-dependent RNA polymerase (70 kDa) were identified by interviral amino acid sequence homologies. For expression of the different ORFs, translational frameshift and readthrough events are proposed.

Nucleotide sequence of beet western yellows virus RNA

The nucleotide sequence of the genomic RNA (5641 nt) of beet western yellow virus (BWYV) isolated from lettuce has been determined and its genetic organization deduced. The sequence of the 3'terminal 2208 nt of RNA of a second BWYV isolate, obtained from sugarbeet, was also determined and was found to be very similar but not identical to that of the lettuce isolate. The complete sequence of BWYV RNA contains six long open reading frames (ORFs). A cluster of three of these ORFs, including the coat protein cistron, display extensive amino acid sequence homology with corresponding ORFs of a second luteovirus, the PAV isolate of barley yellow dwarf virus (BYDV) (1,2). The ORF corresponding to the putative viral RNA-dependant RNA polymerase, on the other hand, resembles that of southern bean mosaic virus. There is circumstantial evidence that expression of the BWYV RNA polymerase ORF may involve a translational frameshift mechanism. The ORF immediately following the coat protein cistron may be translated by in-frame readthrough of the coat protein cistron amber termination codon. Similar mechanisms have been proposed for expression of the corresponding ORFs of BYDV(PAV) (1).