In April 2023, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. The phylum was expanded by one new family, 14 new genera, and 140 new species. Two genera and 538 species were renamed. One species was moved, and four were abolished. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV.

In March 2022, following the annual International Committee on Taxonomy of Viruses (ICTV) ratification vote on newly proposed taxa, the phylum Negarnaviricota was amended and emended. The phylum was expanded by two new families (bunyaviral Discoviridae and Tulasviridae), 41 new genera, and 98 new species. Three hundred forty-nine species were renamed and/or moved. The accidentally misspelled names of seven species were corrected. This article presents the updated taxonomy of Negarnaviricota as now accepted by the ICTV.

Mosaic diseases caused by tobamoviruses have posed significant threats to tomato production. In this review, we overview studies of tomato mosaic diseases published over the past century, which have led to several important discoveries in plant virology, such as the application of attenuated strains. A resistance breeding program established in the 1970s successfully controlled tomato mosaic virus for over 40 years; however, newly emerging tobamoviruses are posing serious challenges in current tomato production. We introduce recent biotechnological attempts to engineer tobamovirus-resistant tomato plants, which offer promising technologies for eradicating the current outbreak.

Shiso (Perilla frutescens var. crispa) is widely grown as an important vegetable or herb crop in Japan. Beginning around the year 2000, occurrences of severe mosaic symptoms on shiso were documented and gradually spread across Kochi Prefecture, one of four major shiso production areas in Japan. Next generation sequencing and cloning indicated the presence of a previously unknown virus related to the members of the genus Emaravirus, for which we proposed the name Perilla mosaic virus (PerMV). The genome of PerMV consists of 10 RNA segments, each encoding a single protein in the negative-sense orientation. Of these proteins, P1, P2, P3a, P3b, P4, and P5 show amino acid sequence similarities with those of known emaraviruses, whereas no similarities were found in P6a, P6b, P6c, and P7. Characteristics of the RNA segments as well as phylogenetic analysis of P1 to P4 indicate that PerMV is a distinct and highly divergent emaravirus. Electron microscopy observations and protein analyses corresponded to presence of an emaravirus. Transmission experiments demonstrated that an eriophyid mite, Shevtchenkella sp. (family Eriophyidae), transmits PerMV with a minimum 30-min acquisition access period. Only plants belonging to the genus Perilla tested positive for PerMV, and the plant−virus−vector interactions were evaluated. The nucleotide sequences reported here are available in the DDBJ/ENA/GenBank databases under accession numbers LC496090 to LC496099.

RNA silencing functions as an antivirus defense strategy in plants, one that plant viruses counter by producing viral suppressors of RNA silencing (VSRs). VSRs have been identified in three members of the genus Crinivirus but they do not all share identical suppression mechanisms. Here, we used Agrobacterium co-infiltration assays to investigate the suppressor activity of proteins encoded by Lettuce chlorosis virus (LCV). Of 7 LCV proteins (1b, P23, HSP70 homolog, P60, CP, CPm, and P27) tested for the suppression of silencing of green fluorescent protein (GFP) expression in wild-type Nicotiana benthamiana plants, only P23 suppressed the onset of local silencing. Small-interfering (si)RNA accumulation was reduced in leaves co-infiltrated with P23, suggesting that P23 inhibited the accumulation or enhanced the degradation of siRNA. P23 also inhibited the cell-to-cell and systemic movement of RNA silencing in GFP-expressing transgenic N. benthamiana plants. Expression of P23 via agroinfiltration of N. benthamiana leaves induced local necrosis that increased in severity at elevated temperatures, a novelty given that a direct temperature effect on necrosis severity has not been reported for the other crinivirus VSRs. These results further affirm the sophistication of crinivirus VSRs in mediating the evasion of host’s antiviral defenses and in symptom modulation.