The genome of the Tenuivirus, Rice stripe virus (RSV) comprises four RNAs, the smallest three of which each contain two open reading frames (ORFs) arranged in an ambisense manner. The expression of the ORFs from RNAs 2-4 in plants and the insect vector, Laodelphax striatellus, was studied using antisera raised against the gene products. In Western blotting of the proteins from infected plants, the molecular masses of p2, p3, pc3 (nucleocapsid protein, N) and p4 (major non-structural protein, NCP) were as expected; that of pc4 appeared larger than expected. Antisera to the N- and C-terminal parts of the complementary ORF on RNA 2, analogous to that encoding glycoproteins on genomes of bunyaviruses and tospoviruses, revealed banding patterns suggestive of processing of the product; the possible processing is discussed. Four types of inclusion bodies were identified by immunofluorescent and immunogold microscopy of thin sections of infected leaves. Most electron-dense amorphous semi-electron-opaque inclusion bodies (dASO) contained only p4 while some contained at least p2, pc2-N, p3, pc3 as well as p4. A ring-like structure containing at least pc2-N, p4 and pc4 was also identified in infected plant cells. Fibrillar amorphous semi-electron-opaque inclusion bodies (fASO) contained only p4. Filamentous electron-opaque inclusion bodies (FEO), which consist of pc2-N(.)and p4, were found both in infected plant cells and in the mid-gut lumen and mid-gut epithelial cells of L. striatellus. This suggests an interaction between p4 and pc2-N and a function of pc2-N distinct from that of its-homologue in Bunyaviridae. Our results confirm the in vivo ambisense coding strategy of Tenuivirus RNA 2 and provide further evidence that RSV does not produce enveloped virions in infected rice plants.

A viral disease with dwarfing symptoms is associated with severe damage of different cereal crops including rice, maize, wheat and sorghum grown in China. It is believed that the pathogenic agent of the disease on rice and sorghum is rice black streaked dwarf virus (RBSDV), however, the cause of maize dwarf disease in China is still inconclusive. In this report, dsRNA was isolated from virus particles obtained from the diseased plants of rice, maize, wheat and sorghum from two Chinese provinces. Full-length cDNAs of genome segments 9 (S9) and 10 (S 10) were obtained through a RT-PCR approach. Sequence analysis showed that the S9 sequences of Chinese isolates and Japanese RBSDV isolate were very similar to each other (89.1-89.6% identity at the nucleotide level, 92.3-92.9% and 95.8-98.6% identity at the amino acid level for ORF1 and ORF2, respectively). In addition, the S10 sequences of Chinese isolates and Japanese RBSDV were very similar to each other (93.0-95.4% identical nucleotides and 96.2-97.0% identical amino acids, respectively). However, there were lower similarities for S9 and S10 sequences between Chinese isolates and an Italian Maize Rough Dwarf Virus (MRDV) isolate. Phylogenetic analysis indicates that Chinese viral isolates found to infect rice, maize, wheat and sorghum and leading to similar cereal dwarfing manifestations could be grouped to the same virus species, RBSDV.

GST fusion proteins of the six gene products from RNAs 2,3 and 4 of the tenuivirus, Rice stripe virus (RSV), were used to study the nucleic acid binding activities in vitro. Three of the proteins, p3, pc3 and pc4, bound both single- and double-stranded cDNA of RSV RNA4 and also RNA3 transcribed from its cDNA clone, while p2, pc2-N (the N-terminal part of pc2) nor p4 bound the cDNA or RNA transcript. The binding activity of p3 is located in the carboxyl-terminus amino acid 154-194, which contains basic amino acid rich beta-sheets. The acidic amino acid-rich amino-terminus (amino acids 1-100) of p3 did not have nucleic acid binding activity. The related analogous gene product of the tenuivirus, Rice hoja blanca virus, is a suppressor of gene silencing and the possibility of the nucleic acid binding ability of RSV p3 being associated with this property is discussed. The C-terminal part of the RSV nucleocapsid protein, which also contains a basic region, binds nucleic acids, which is consistent with its function. The central and C-terminal regions of pc4 bind nucleic acid. It has been suggested that this protein is a cell-to-cell movement protein and nucleic acid binding would be in accord with this function.