M. A. Mayo

A summary of taxonomic changes recently approved by ICTV.

A number of taxonomic proposals were approved by the Executive Committee of the International Committee on Taxonomy of Viruses (ICTV) at its meeting in Houston earlier this year. These are listed in [1]. These proposals have now been approved by a vote of the full ICTV, as required by ICTV Statutes [2]. The resulting changes include the creation of 6 new families and 8 new genera. These are listed below in Tables 1 and 2 respectively. Names of three genera were also changed (Table 3). The other changes are to the lists, and in a few instances the names, of species classified in particular genera. For a listing of these changes, the reader is referred to the detailed listing of the proposals in [1].

Virus taxonomy - Houston 2002.

The 30th meeting of the Executive Committee of the International Committee on Taxonomy of Viruses (ICTV) was held at Baylor College of Medicine, Texas Medical Center, Houston, Texas on the 7th and 8th of March of this year. In addition to the regular reviews of ICTV circumstances and procedures, there were three main items of business. These were taxonomic proposals, the ICTV database and ICTV activities at the coming International Virology Congress. The taxonomic proposals discussed are listed below. Most of these had been available for public inspection for some time on the ICTVnet public message board. The proposals are now being examined by the full ICTV membership who will vote to accept or reject them. Those accepted will be reported in future notes in Virology Division News. The taxonomic proposals were:

Distribution of Determinants for Symptom Production, Host Range and Nematode Transmissibility between the two RNA Components of Raspberry Ringspot Virus

Summary Raspberry ringspot virus has two RNA species, of mol. wt. about 2.4 × 106 (RNA-1) and 1.4 × 106 (RNA-2). In experiments with four naturally occurring strains, virus hybrids were made by mixing RNA-1 and RNA-2 preparations from different strains. Parent strains were regenerated by crossing appropriate hybrids. In the crosses, both serological specificity and transmissibility by the nematode Longidorus elongatus were determined by RNA-2, suggesting that the protein surface of the virus particles is involved in the transmission process. Ability of isolates to cause systemic yellowing in Petunia hybrida, previously found to be also controlled by RNA-2, was shown to be associated with distinctive ultrastructural changes in the chloroplasts. Severity of systemic symptoms in Chenopodium quinoa and other herbaceous hosts, ability to infect Lloyd George raspberry and ability to invade the non-inoculated leaves of Phaseolus vulgaris, were all determined by RNA-1. Both RNA species played a part in determining lesion type in inoculated leaves of Chenopodium amaranticolor and C. quinoa, and in some crosses the two kinds of hybrid were respectively less virulent and more virulent than either parent. The determinant for systemic symptoms in Petunia hybrida that is carried by RNA-2 was not expressed when in association with RNA-1 from the strain able to infect Lloyd George raspberry. Some genes of raspberry ringspot virus are probably pleiotropic.

Virus nomenclature: consensus versus chaos.

A recent, highly polemical contribution to these columns [10] criticized the workings of the International Committee on Taxonomy of Viruses (ICTV) and suggested that the new Rules about the orthography of virus species names approved by ICTV were leading virus nomenclature into chaos. References to receding or impending chaos are frequently made by those who approve [6, 7] or disapprove [10] of the work done by the ICTV on behalf of the world community of virologists. In his one-sided and unbalanced diatribe against the work of the ICTV, Gibbs [10] raises several issues that need to be answered. We have gauged the opinions of the ICTV Executive Committee and of the ICTV Life Members regarding the various criticisms levelled by Gibbs and summarize the responses below. Several of the respondents deplored the derogatory tone used by Gibbs to refer to the activities of the ICTV, an organization of which he is a Life Member, and stated that they regard the ICTV as a valuable international body which, in spite of certain organizational concerns, has served virologists well.

Evidence that Potato Leafroll Virus RNA is Positive-stranded, is Linked to a Small Protein and Does Not Contain Polyadenylate

Summary RNA extracted from particles of potato leafroll virus (PLRV) infected tobacco mesophyll protoplasts. Treating the RNA with proteinase K did not abolish its infectivity. In messenger-dependent rabbit reticulocyte lysate, PLRV RNA induced the synthesis of specific polypeptides: a major product of mol. wt. 71000 but no product the size of coat protein. PLRV RNA is therefore positive-stranded. A genome-linked protein (apparent mol. wt. 7000) was detected in preparations of PLRV RNA but no polyadenylate sequence was found. These features may prove to be characteristic of luteoviruses.

Changes to virus taxonomy 2004

This note presents a compilation of recent changes to virus taxonomy decided by voting by the ICTV membership following recommendations from the ICTV Executive Committee. The changes are presented in the Table as decisions promoted by the Subcommittees of the EC and are grouped according to the major hosts of the viruses involved. These new taxa will be presented in more detail in the 8th ICTV Report scheduled to be published near the end of 2004 (Fauquet et al., 2004). Fauquet, C.M., Mayo, M.A., Maniloff, J., Desselberger, U., and Ball, L.A. (eds) (2004). Virus Taxonomy, VIIIth Report of the ICTV. Elsevier/Academic Press, London, pp. 1258.

Properties of Virus and RNA Components of Raspberry Ringspot Virus

Summary Particles of raspberry ringspot virus were homogeneous in immunoelectrophoresis tests but sedimented as three components, T, M and B, with sedimentation coefficients of 52, 92 and 130s respectively, and containing 0, 30 and about 44% RNA. The three components were serologically indistinguishable. In CsCl gradients, M and B were each homogeneous, with buoyant densities of 1.43 and 1.52 g./cm.3 respectively. Infectivity was associated with B. RNA extracted from the virus preparations was single-stranded and showed about 20% hyperchromicity in 0.1 m-sodium phosphate buffer at pH 7.0, indicating about 40% base-pairing. Analysis of RNA preparations by polyacrylamide gel electrophoresis revealed two predominant RNA species with mol. wt of 2.4 × 106 (RNA-1) or 1.4 × 106 (RNA-2); RNA-2 was indistinguishable in mol. wt from the RNA-2 of tobacco ringspot virus but RNA-1 migrated slightly more slowly than the RNA-1 of tobacco ringspot virus. M particles of raspberry ringspot virus contain one molecule of RNA-2; B particles contain either one molecule of RNA-1 or, probably, two molecules of RNA-2. Whereas B particles of raspberry ringspot virus were apparently homogeneous in CsCl gradients, B particles of tobacco ringspot virus formed two buoyant density classes.

Abbreviations for plant virus names – 1999

Whilst it is obvious that a bureaucratic fondness for abbreviations has exposed their use to sharp, and deserved, ridicule, they nonetheless can satisfy a genuine need. In virology, it is a commonplace that abbreviations for virus names make the literature both easier to read and more succinct to present. The International Committee for Taxonomy of Viruses (ICTV) is responsible for controlling, approving and recording the names of virus taxa and has a formal International Code that guides this activity. However, there is an important distinction between formal names for taxa and abbreviations, for which ICTV does not have a constitutional responsibility. ICTV does publish abbreviations in its Reports, and is often asked for guidance concerning the “correct” abbreviation to use. Nonetheless, these are advisory rather than mandatory. Traditionally, abbreviations have been regarded as strictly local to a particular paper, chapter or thesis. Thus at one time “AMV” was used equally for Arabis mosaic virus , Alfalfa mosaic virus and Avian myeloblastosis virus , but not in the same piece of writing. Equally, “CMV” is a commonly used abbreviation for Cucumber mosaic virus , but is also used for Cytomegalovirus. Currently, there are about 4000 virus names in the ICTV lists and it is impractical to define unique abbreviations for them all. But within a discipline it should be possible. And if abbreviations are to be used, it is obviously a great convenience if an agreed standard abbreviation can be used for any particular virus in all published work. For plant virology, a set of principles has been developed to guide in the creation of new abbreviations and in attempts to standardize usage. These principles have been published [1, 2], and those discussed here are based on them.

Polyadenylate in the RNA of Five Nepoviruses

Summary RNA extracted from particles of five nepoviruses [raspberry ringspot (RRV), strawberry latent ringspot, tobacco ringspot (TRSV), tomato black ring (TBRV) and tomato ringspot viruses] was bound to oligo(dT)-cellulose in buffers of high ionic strength (HS) whereas RNA from particles of tobacco mosaic virus or tobacco rattle virus was not. This suggests that nepovirus RNA molecules contain polyadenylate [poly(A)]. At least 97% of the infective RNA molecules of TRSV and TBRV were bound in HS buffer and eluted in buffer of low ionic strength. The two species of genome RNA of RRV and TBRV were bound equally to oligo(dT)-cellulose, but the satellite RNA (RNA-3) of TBRV was bound less avidly and to a smaller extent than the genome RNA. When 3H-borohydride-labelled TRSV RNA was digested with ribonucleases A + T1 about 29% of the radioactivity bound to oligo(dT)-cellulose, presumably as polyadenylate. Adenosine trialcohol was the only nucleoside trialcohol detected in alkali digests of borohydride-labelled RNA. Thus polyadenylate is probably located at the 3′-termini of the RNA molecules.

Replication of RNA-1 of tomato black ring virus independently of RNA-2.

Summary In hybridization experiments, using complementary DNA (cDNA) copies of the two genome parts of tomato black ring virus (TBRV RNA-1 and RNA-2), no sequence homology between the two RNA species was detected. When tobacco mesophyll protoplasts were inoculated with purified middle component particles, which contain only RNA-2, no replication of TBRV RNA could be detected. However, when they were inoculated with purified bottom component particles, which contain only RNA-1, extracts made 24 or 48 h later contained RNA that had the same mobility as RNA-1 in polyacrylamide-agarose gels, and that hybridized to cDNA copies of RNA-1. Thus RNA-1 can replicate in protoplasts that do not contain RNA-2. Moreover, this RNA-1 was capable, when mixed with nucleoprotein particles containing RNA-2, of inducing the formation of local lesions in Chenopodium amaranticolor leaves, and therefore was intact and attached to the genome-linked protein. The genome-linked protein of nepoviruses is probably virus-coded, and its production in protoplasts inoculated with bottom component particles therefore suggests that RNA-1 contains the gene for this protein.