Purification and coat protein gene sequence of a Montana RMV-like isolate of barley yellow dwarf virus

The complete nucleotide sequence of the genome of Barley yellow dwarf virus-RMV reveals it to be a new Polerovirus distantly related to other yellow dwarf viruses

The yellow dwarf viruses (YDVs) of the Luteoviridae family represent the most widespread group of cereal viruses worldwide. They include the Barley yellow dwarf viruses (BYDVs) of genus Luteovirus, the Cereal yellow dwarf viruses (CYDVs) and Wheat yellow dwarf virus (WYDV) of genus Polerovirus. All of these viruses are obligately aphid transmitted and phloem-limited. The first described YDVs (initially all called BYDV) were classified by their most efficient vector. One of these viruses, BYDV-RMV, is transmitted most efficiently by the corn leaf aphid, Rhopalosiphum maidis. Here we report the complete 5612 nucleotide sequence of the genomic RNA of a Montana isolate of BYDV-RMV (isolate RMV MTFE87, Genbank accession no. KC921392). The sequence revealed that BYDV-RMV is a polerovirus, but it is quite distantly related to the CYDVs or WYDV, which are very closely related to each other. Nor is BYDV-RMV closely related to any other particular polerovirus. Depending on the gene that is compared, different poleroviruses (none of them a YDV) share the most sequence similarity to BYDV-RMV. Because of its distant relationship to other YDVs, and because it commonly infects maize via its vector, R. maidis, we propose that BYDV-RMV be renamed Maize yellow dwarf virus-RMV (MYDV-RMV).

Genetic structure in natural populations of barley/cereal yellow dwarf virus isolates from Alaska

The genetic structure of natural populations of Alaskan barley yellow dwarf virus (BYDV)-PAV, BYDV-PAS, and cereal yellow dwarf virus (CYDV)-RPV from barley (Hordeum vulgare L.) and oats (Avena sativa L.) in Alaska were analyzed between 2002 and 2004. PCR products spanning the viral coat protein gene of 187 isolates were cloned and sequenced. The majority (78%) were similar to BYDV-PAS, 19% were similar to CYDV-RPV, and only about 3% resembled BYDV-PAV. The CYDV-RPV isolates clustered in three groups: 44, 17, and 39% resembled RPS-like CP from Mexico, resembled RPV-like CP from New York, or formed a unique clade that was RPV/RPS recombinant CP, respectively. The patterns of genetic variation of PAS and RPV varied little over time or with respect to host plant. The difference in spatial and temporal population genetic structures of the PAS and RPV isolates suggests that these two viruses are influenced by different agroecological factors. Sequence of PCR products spanning the carboxyl terminus of the polymerase gene, the intergenic region, and most of the coat protein gene of RPV revealed two probable ancestral recombination events for some isolates.

Genetic analysis of a novel Alaska barley yellow dwarf virus in the family Luteoviridae

A new plant virus belonging to the family Luteoviridae and isolated from diseased oat (Avena sativa L.) plants was discovered in Alaska in 2003. Even though plants with red/orange leaves were indicative of barley yellow dwarf disease, they were not reactive to specific antibodies corresponding to barley yellow dwarf virus (BYDV)-MAV, -PAV, -SGV, and cereal yellow dwarf virus-RPV from enzyme-linked immunosorbent assays (ELISA). An alternative RT-PCR assay that incorporated Shu-F/Yan-R primers for detection of BYDV-MAV, -PAS, -PAV, and SGV was effective in producing approximately 830-nt fragments that contained genomic sequences to the 3'-terminus of the polymerase gene (ORF 2), the intergenic region ( approximately 113 nt), the coat protein gene (ORF 3), and the putative movement gene (ORF 4). The Alaskan isolates were most similar to BYDV-MAV with only about 77 and 80% amino acid identity in the CP and ORF 4, respectively. The Alaska isolates coat protein gene sequences differed in several regions that otherwise are conserved among BYDV-MAV isolates, and may be important in serological variations, accounting for the negative ELISA results. Based upon sequence and serological differences, we concluded that the Alaskan BYDV-MAV-like isolates formed a novel species tentatively in the genus Luteovirus, and propose the name BYDV-ORV (oat red-leaf virus).

Variation in Transmission Efficiency Among Barley yellow dwarf virus-RMV Isolates and Clones of the Normally Inefficient Aphid Vector, Rhopalosiphum padi

The RMV strain of Barley yellow dwarf virus (BYDV-RMV) is an unassigned member of the Luteoviridae that causes barley yellow dwarf in various cereal crops. The virus is most efficiently vectored by the aphid Rhopalosiphum maidis, but can also be vectored with varying efficiency by R. padi and Schizaphis graminum. Field collections of alate aphids migrating into the emerging winter wheat crop in the fall of 1994 in central New York identified a high proportion of R. padi transmitting BYDV-RMV. This prompted a comparison of the BYDV-RMV isolates and the R. padi populations found in the field with type virus and aphid species maintained in the laboratory. A majority of the field isolates of BYDV-RMV were similar to each other and to the type BYDV-RMV isolate in disease severity on oat and in transmission by the laboratory-maintained population of R. maidis and a field-collected population of R. maidis. However, several field populations of R. padi differed in their ability to transmit the various BYDV-RMV isolates. The transmission efficiency of the R. padi clones was increased if acquisition and inoculation feeding periods were allowed at higher temperatures. In addition, the transmission efficiency of BYDV-RMV was significantly influenced by the aphid that inoculated the virus source tissue. In general, BYDV-RMV transmission by R. padi was higher when R. padi was the aphid that inoculated the source tissue than when R. maidis was the inoculating aphid. The magnitude of the change varied among virus isolates and R. padi clones. These results indicate that, under certain environmental conditions, R. padi can play a significant role in the epidemiology of BYDV-RMV. This may be especially significant in regions where corn is a major source of virus and of aphids that can carry virus into a fall-planted wheat crop.

Molecular and Biological Characterization of a Trackable Illinois Isolate of Barley yellow dwarf virus-PAV

In consecutive annual statewide surveys of the incidence of Barley yellow dwarf viruses (BYDVs) in Illinois wheat and oat fields, 27 BYDV-PAV-like isolates were identified. Using polymerase chain reaction (PCR), the coat protein regions of all 27 isolates were analyzed for restriction fragment length polymorphisms. The PCR products of two isolates, one from each year, had restriction fragment profiles after digestion with HaeIII that differed from the other isolates. The nucleotide sequences of the coat protein regions of a laboratory isolate, BYDV-PAV-IL (PAV-IL), two of the isolates with the common restriction profile, and the two isolates with polymorphic profiles were more than 98% identical. The relatively rare isolate identified during the first year was designated BYDV-PAV-DK1 (PAV-DK1) and further characterized biologically. PAV-DK1 and PAV-IL did not differ significantly in symptom expression, but did differ significantly in rates of transmission by two of the three biotypes of Rhopalosiphum padiexamined. Since PAV-DK1 does not occur in high levels in the state of Illinois, and its PCR products have a unique restriction enzyme profile, it has the potential to be used as a traceable isolate in field epidemiological experiments.

Asymmetrical Distribution of Barley Yellow Dwarf Virus PAV Variants Between Host Plant Species

ABSTRACT A large epidemiological study of the genetic variation of barley yellow dwarf virus (BYDV) serotype PAV involving different host plant species was conducted. French BYDV PAV isolates were collected from barley and ryegrass, and their capsid protein gene sequences characterized using restriction fragment length polymorphism, single-strand conformation polymorphism, and sequence analyses. The data show that BYDV PAV isolates from five different continents are separated into two distinct groups named cpA and cpB, which are distributed irrespective of geographical location. Amino acid identity of the capsid proteins ranged from 93 to 99.5% in group cpA and from 95 to 99.5% in group cpB, while this value was only from 82 to 88% between the groups. Moreover, isolates from each group were found preferentially (up to 98%) in one of the two plant species examined. These results show that host plant species play a role in isolate selection and maintenance and that they contribute to the genetic diversity of BYDV PAV.

Purification and coat protein gene sequence of a Montana RMV-like isolate of barley yellow dwarf virus

A Montana barley yellow dwarf virus (BYDV) isolate, BYDV-RMV-MT, is serologically identical to the New York RMV type isolate (RMV-NY) but differs in aphid transmission phenotype. A purification procedure for BYDV-RMV-MT was developed and cDNAs encompassing the entire coat protein gene and a portion of the putative polymerase gene of both RMV-MT and RMV-NY were cloned and sequenced. Diameters of RMV-MT virions averaged 24.7 nm. Average virus yield was 4.2 mg/kg plant tissue. There was 81% sequence identity between the clones of MT and NY RMV isolates at the nucleotide level. At the amino acid level the polymerase genes were 91% identical to each other and 74% homologous with that of beet western yellow virus. The coat protein amino acid sequences of the two RMV isolates were only 81% identical and, compared to other sequenced luteoviruses, both were most similar to cucurbit aphid-borne yellows virus.