The nucleotide sequence of Indian peanut clump virus RNA 2: sequence comparisons among pecluviruses

Tropical food legumes: virus diseases of economic importance and their control

Diverse array of food legume crops (Fabaceae: Papilionoideae) have been adopted worldwide for their protein-rich seed. Choice of legumes and their importance vary in different parts of the world. The economically important legumes are severely affected by a range of virus diseases causing significant economic losses due to reduction in grain production, poor quality seed, and costs incurred in phytosanitation and disease control. The majority of the viruses infecting legumes are vectored by insects, and several of them are also seed transmitted, thus assuming importance in the quarantine and in the epidemiology. This review is focused on the economically important viruses of soybean, groundnut, common bean, cowpea, pigeonpea, mungbean, urdbean, chickpea, pea, faba bean, and lentil and begomovirus diseases of three minor tropical food legumes (hyacinth bean, horse gram, and lima bean). Aspects included are geographic distribution, impact on crop growth and yields, virus characteristics, diagnosis of causal viruses, disease epidemiology, and options for control. Effectiveness of selection and planting with virus-free seed, phytosanitation, manipulation of crop cultural and agronomic practices, control of virus vectors and host plant resistance, and potential of transgenic resistance for legume virus disease control are discussed.

Targeting highly conserved 3'-untranslated region of pecluviruses for sensitive broad-spectrum detection and quantitation by RT-PCR and assessment of phylogenetic relationships

The 3'-end region of many virus isolates has been shown to possess conserved sequences in addition to the presence of numerous genomic and subgenomic RNAs. Utilizing these sequences, a broad-spectrum reverse transcription-polymerase chain reaction protocol has been developed to detect all the known Indian peanut clump virus and Peanut clump virus isolates, that cause peanut clump diseases in West Africa and India. The primers were targeted at the highly conserved 3'-untranslated regions of the PCV RNA-1 and RNA-2. The conservation was confirmed by sequencing these untranslated regions of RNA-1 for six isolates and RNA-2 for one isolate. The conserved structure of the RNA-1 and RNA-2 was observed and the importance of this region for the virus survival was confirmed. The primers were also designed for virus quantitation using a Taqman(®)-based real-time RT-PCR. The use of RT-PCR and real-time quantitative RT-PCR improved the sensitivity of PCV detection compared to ELISA. RT-PCR also led to the detection of IPCV and PCV on two new natural hosts: Oldenlandia aspera and Vigna subterranea. Real-time RT-PCR is considered to be an ideal tool for identifying resistant sources to both IPCV and PCV.

Genome Structure and Production of Biologically Active In Vitro Transcripts of Cucurbit-Infecting Zucchini green mottle mosaic virus

ABSTRACT The complete nucleotide sequence of the Zucchini green mottle mosaic virus (ZGMMV), a new member of the genus Tobamovirus, has been determined. The genome of ZGMMV is 6,513 nucleotides long and contains four open reading frames coding for proteins of 131, 189, 28, and 17 kDa from the 5' to 3' end, respectively. The 5'- and 3'-non-translated regions consist of 59 and 163 residues, respectively. The sequences of the viral proteins exhibit high identity to the proteins of the members of the genus Tobamovirus and are distinct from other viruses within the subgroup of cucurbit-infecting tobamoviruses. Results from phylogenetic trees of the coding regions demonstrated that ZGMMV is a very close relative of Kyuri green mottle mosaic virus and Cucumber fruit mottle mosaic virus and is less similar to Cucumber green mottle mosaic virus. Full-length cDNA of ZGMMV was directly amplified by reverse-transcription polymerase chain reaction (RT-PCR) using the 5'-end primer containing a T7 RNA promoter sequence and 3'-end primer. Capped in vitro transcript from the RT-PCR products was infectious on zucchini squash, cucumber, and Nicotiana benthamiana plants. This cell-free system to produce infectious transcripts from uncloned cDNA copies is useful for quick assessment of infectivity of transcripts from plant RNA viruses prior to cloning. Synthesized capped transcript from a full-length cDNA clone of the virus was highly infectious. Progeny virus derived from infectious transcripts had the same biological and biochemical properties as wild-type virus. To our knowledge, this is the first report of a biologically active transcript from a cucurbit-infecting tobamovirus.

The valine anticodon and valylatability of Peanut clump virus RNAs are not essential but provide a modest competitive advantage in plants

The role of valine aminoacylation of the two genomic RNAs of Peanut clump virus (PCV) was studied by comparing the amplification in vivo of RNAs with GAC, GDeltaC, or CCA anticodons in the tRNA-like structure (TLS) present at the 3' end of each viral RNA. The PCV RNA1 TLS of isolate PCV2 possesses a GAC anticodon and is capable of highly efficient valylation, whereas the RNA2 TLS has a GDeltaC anticodon that does not support valylation. The presence in RNA1 of GDeltaC or CCA anticodons that conferred nonvalylatability resulted in about 2- to 4-fold and a 14- to 24-fold reduction, respectively, in RNA accumulations in tobacco BY-2 protoplasts inoculated with the RNA1 variants together with wild-type RNA2(GDeltaC). No differences in RNA levels were observed among protoplasts inoculated with the three variant RNA2s in the presence of wild-type RNA1(GAC). All combinations of valylatable and nonvalylatable RNAs 1 and 2 were similarly infectious in Nicotiana benthamiana plants, and viral RNAs accumulated to similar levels; all input TLS sequences were present unchanged in apical leaves. In direct competition experiments in N. benthamiana plants, however, both RNA1 and RNA2 with GAC valylatable anticodons outcompeted the nonvalylatable variants. We conclude that valylation provides a small but significant replicational advantage to both PCV RNAs. Sequence analysis of the TLS from RNA2 of a second PCV isolate, PO2A, revealed the presence of an intact GAC valine anticodon, suggesting that the differential valylation of the genomic RNAs of isolate PCV2 is not a general characteristic of PCV.