The results of the meetings of the International Committee on Taxonomy of Viruses, held in Madrid, September 1975, are briefly reported: rules of viral nomenclature, composition of the new Executive Committee, and a list of the names so far officially agreed. Introduction The International Committee on the Taxonomy of Viruses (ICTV), which is a committee of the Section on Virology of the International Association of Microbiological Societies (IAMS), completed a round of meetings during the Third International Congress for Virology that was held in Madrid from September 10--17, 1975. Since ICTV only meets during these conferences, which are held every four years, the meetings are important occasions for reviewing the classification and nomenclature of viruses. Decisions on new names, which encapsulate the recognition of natural "groups" of viruses, evolve slowly. Official approval for new names depends upon a series of sequential steps ; recommendations by one or more of the subcommittees of the Executive Committee of ICTV (subcommittees on Bacterial, Invertebrate, Plant and Vertebrate Viruses respectively, and for some of the larger viral groups which span several kinds of hos t s the Coordination Subcommittee), which are considered by the Executive Committee of ICTV and may finally be submitted for approval by ICTV itself. Only after this final approval does a name become "official". The results of the last five years of work by ICTV and its committees will be published early this year as a separate volume of "Intervirology", the official journal of the Section on Virology of IAMS, and additional copies will be produced for sale as separates. This "Second P~eport" will include, besides "approved" and common names of virus groups, a brief description of the properties of each

Classification and Nomenclature of Viruses

The majority of described plant viruses are transmitted by insects of the Hemipteroid assemblage that includes aphids, whiteflies, leafhoppers, planthoppers, and thrips. In this review we highlight progress made in research on vector interactions of the more than 200 plant viruses that are transmitted by hemipteroid insects beginning a few hours or days after acquisition and for up to the life of the insect, i.e., in a persistentcirculative or persistent-propagative mode. These plant viruses move through the insect vector, from the gut lumen into the hemolymph or other tissues and finally into the salivary glands, from which these viruses are introduced back into the plant host during insect feeding. The movement and/or replication of the viruses in the insect vectors require specific interactions between virus and vector components. Recent investigations have resulted in a better understanding of the replication sites and tissue tropism of several plant viruses that propagate in insect vectors. Furthermore, virus and insect proteins involved in overcoming transmission barriers in the vector have been identified for some virus-vector combinations.

Insect Vector Interactions with Persistently Transmitted Viruses

As a first step towards development of insect resistant rice we have introduced a truncated δ-endotoxin gene, cryIA(b) of Bacillus thuringiensis (B.t.) which has specific biological activity against lepidopteran insects into a japonica rice. To highly express the cryIA(b) gene in rice the coding sequence was extensively modified based on the codon usage of rice genes. Transgenic plants efficiently expressed the modified cryIA(b) gene at both mRNA and protein levels. Bioassays using R2 generation plants with two major rice insect pests, striped stemborer (Chilo suppressalis) and leaffolder (Cnaphalocrosis medinalis), indicated that transgenic rice plants expressing the CrylA(b) protein are more resistant to these pests than untransformed control plants. Our results suggest that the B.t. endotoxin genes will be useful for the rational development of new rice varieties resistant to major insect pests.

Insect Resistant Rice Generated by Introduction of a Modified δ-endotoxin Gene of Bacillus thuringiensis

We introduced the potato proteinase inhibitor II (PINII) gene (pin2) into several Japonica rice varieties, and regenerated a large number of transgenic rice plants. Wound-inducible expression of the pin2 gene driven by its own promoter, together with the first intron of the rice actin 1 gene (act1), resulted in high-level accumulation of the PINII protein in the transgenic plants. The introduced pin2 gene was stably inherited in the second, third, and fourth generations, as shown by molecular analyses. Based on data from the molecular analyses, several homozygous transgenic lines were obtained. Bioassay for insect resistance with the fifth-generation transgenic rice plants showed that transgenic rice plants had increased resistance to a major rice insect pest, pink stem borer (Sesamia inferens). Thus, introduction of an insecticidal proteinase inhibitor gene into cereal plants can be used as a general strategy for control of insect pests.

Transgenic rice plants harboring an introduced potato proteinase inhibitor II gene are insect resistant

Relationships among the amino acid sequences of viral movement proteins related to the 30 kDa ('30K') movement protein of tobacco mosaic virus - the 30K superfamily - were explored. Sequences were grouped into 18 families. A comparison of secondary structure predictions for each family revealed a common predicted core structure flanked by variable N- and C-terminal domains. The core consisted of a series of b-elements flanked by an a-helix on each end. Consensus sequences for each of the families were generated and aligned with one another. From this alignment an overall secondary structure prediction was generated and a consensus sequence that can recognize each family in database searches was obtained. The analysis led to criteria that were used to evaluate other virus-encoded proteins for possible membership of the 30K superfamily. A rhabdoviral and a tenuiviral protein were identified as 30K superfamily members, as were plant- encoded phloem proteins. Parsimony analysis grouped tubule-forming movement proteins separate from others. Establishment of the alignment of residues of diverse families facilitates comparison of mutagenesis experiments done on different movement proteins and should serve as a guide for further such experiments.

https://www.researchgate.net/profile/Ulrich_Melcher/publication/200036577_The_30K_superfamily_of_viral_movement_proteins/links/02e7e53be9a1e4722c000000.pdf

The '30K' superfamily of viral movement proteins.

The coat protein (CP) gene of rice stripe virus was introduced into two japonica varieties of rice by electroporation of protoplasts. The resultant transgenic plants expressed the CP at high levels (up to 0.5% of total soluble protein) and exhibited a significant level of resistance to virus infection. Plants derived from selfed progeny of the primary transformants also expressed the CP and showed viral resistance, indicating stable transmission of the CP gene and the trait of resistance to the next generation. Moreover, the virally encoded strip disease-specific protein was not detected in transgenic plants expressing CP 8 weeks after inoculation, indicating protection before viral multiplication. These studies demonstrated that CP-mediated resistance to virus infection can be extended to cereals and to the viruses transmitted by an insect vector (planthopper).

https://www.pnas.org/content/pnas/89/20/9865.full.pdf

Genetically engineered rice resistant to rice stripe virus, an insect-transmitted virus.

The complete nucleotide sequence of RNA 1, the largest genomic segment of rice stripe virus (RSV), was determined using two sets of overlapping cDNA clones. RNA segment 1 comprises 8970 nucleotides and on the viral complementary sequence has a single long open reading frame coding for a protein of 2919 amino acids with an estimated M r of 336860. Amino acid sequence comparisons of the putative protein indicated strong homology (30% amino acid identity over about 1500 residues) with the L protein of the genus Phlebovirus of the Bunyaviridae, but no detectable similarity with other members of the Bunyaviridae. However, weak similarity was detected with the L protein of Tacaribe arenavirus. The highly homologous sequence domain includes the conserved motifs of the putative RNA-dependent RNA polymerase. The data presented here, along with previous work clearly show significant similarities in genome organization, structure and expression between RSV and members of the genus Phlebovirus of the Bunyaviridae. Taken together, we propose that tenuiviruses should be included in the Bunyaviridae under the genus Tenuivirus.

Nucleotide sequence of RNA 1, the largest genomic segment of rice stripe virus, the prototype of the tenuiviruses

The complete nucleotide sequence (3514 nucleotides) of RNA segment 2 of rice stripe virus (RSV), the prototype member of tenuivirus group, was determined. In the virus-sense RNA an open reading frame (ORF) is present which encodes a 199 amino acid protein of M
r 22762. Another long ORF encoding an 834 amino acid protein with M
r 94047 (94K) exists in the virus-complementary RNA. Between these two ORFs, there is a long non-coding intergenic region of 299 nucleotides. The sequence suggests that RNA 2 has an ambisense coding strategy as found for RSV RNAs 3 and 4. The putative 94K protein carries stretches with an amino acid sequence showing weak similarity to parts of the membrane glycoproteins of Punta Toro and Uukuniemi phleboviruses of the family Bunyaviridae, suggesting a possible distinct evolutionary relationship between the animal phleboviruses and the plant tenuiviruses.

Nucleotide sequence and possible ambisense coding strategy of rice stripe virus RNA segment 2

The RNA 3 of rice stripe virus (RSV) isolate T was cloned and its nucleotide sequence was determined. The complete primary structure was found to consist of 2504 nucleotides. One putative open reading frame (ORF), between nucleotides 2412 and 1444 in the 5′-proximal region of the virus complementary-sense RNA, encoded a 322 amino acid protein with an M
r of 35134 that was identified as the coat protein. The other ORF, between nucleotides 66 and 701 in the 5′-proximal region of the virus-sense RNA, encoded a 211 amino acid protein with an M
r of 23 874. An intergenic non-coding region (742 nucleotides) between the two ORFs contains oligo(A)- and oligo(U)-rich regions that can be arranged into a 126 base pair stem configuration. These results suggest that RSV RNA 3 has an ambisense coding strategy.

Complete nucleotide sequence of RNA 3 of rice stripe virus: an ambisense coding strategy.

The complete nucleotide sequence of RNA 4 of rice stripe virus isolate T (RSV-T) was determined and found to consist of 2157 nucleotides, containing two open reading frames (ORFs). One, deduced to be present in the 5′-proximal region of the viral-sense RNA, encodes the stripe disease-specific protein with M
r 20541, and the other ORF, in the 5′-proximal region of the viral complementary sense RNA, encodes an unknown protein with M
r 32474. Between these two ORFs there is an intergenic non-coding region that could form a secondary structure with two base-paired hairpin configurations. These characteristics indicate that RSV-T RNA 4 has an ambisense coding strategy. Comparison of the two ORFs of RSV-T with those of another isolate revealed 97.2% and 98.0% identity for the nucleotide sequences, and 98.3% and 98.2% identity for the amino acid sequences. The leader sequences of these two isolates were the same. However, an insertion was found in the intergenic non-coding region of RSV-T. Furthermore, comparison of the nucleotide and amino acid sequences of RSV-T RNA 4 with those of RNA 4 of maize stripe virus, which is another member of the tenuivirus group, revealed greater identity, suggesting a close phylogenetic relationship between these two viruses.

Shigemitsu Toriyama

Papers

Genetically engineered rice resistant to rice stripe virus, an insect-transmitted virus.

Nucleotide sequence of RNA 1, the largest genomic segment of rice stripe virus, the prototype of the tenuiviruses

Nucleotide sequence and possible ambisense coding strategy of rice stripe virus RNA segment 2

Complete nucleotide sequence of RNA 3 of rice stripe virus: an ambisense coding strategy.

Complete nucleotide sequence of RNA 4 of rice stripe virus isolate T, and comparison with another isolate and with maize stripe virus.