Scopolia mild mottle virus: a new tobamovirus isolated from a Scopolia japonica plant in Japan.

A tobamovirus was isolated from leaves of a Scopolia japonica plant showing mild yellowing. Back-inoculation of healthy Scopolia japonica with the isolated virus induced mild mottle on upper leaves. Phylogenetic analysis based on coat protein and replicase protein sequences revealed that the newly isolated tobamovirus was most closely related to yellow tailflower mild mottle virus (YTMMV). The newly isolated tobamovirus shared the highest nucleotide sequence identity (71%) with YTMMV, which is lower than the cutoff (90%) set for species demarcation in the genus Tobamovirus. Thus, our result suggested that scopolia mild mottle virus (SMMoV) is a new tobamovirus that infects Scopolia japonica plants in Japan.

Complete genome sequence of Sikte (Sitke) waterborne virus, a member of the genus Tombusvirus.

The 4704-nt genome sequence of Sikte waterborne virus (SWV), determined by fragmented and primer ligated dsRNA sequencing and by direct Sanger sequencing, is linear, nonsegmented and has the five ORFs of other tombusviruses. The 5' and 3' untranslated regions (UTRs) are 150 and 335 nt long, respectively. Phylogenetic analysis of the coat protein revealed that SWV is related to CymRSV and PNSV, but that of the SWV replicase protein, the p92 readthrough protein, indicated a close relationship to CNV. These phylogenetic analyses suggest the occurrence of recombination events in SWV, as reported previously for other tombusviruses.

Characterization of a new carmovirus isolated from an Adonis plant.

An isometric virus was isolated from a cultivated Adonis plant (A. ramosa). The purified virus particle is 28 nm in diameter and is composed of a single coat protein and a single RNA genome of 3,991 nucleotides. Sequence analysis showed that the virus is closely related to carnation mottle virus. The virus was used to mechanically infect healthy A. ramosa plants, resulting in mosaic and leaf curl symptoms; however, attempts to inoculate carnation plants did not result in infection. We propose the virus as a new carmovirus and have named it adonis mosaic virus (AdMV).

Complete genome sequences of two highly divergent Japanese isolates of Plantago asiatica mosaic virus.

Plantago asiatica mosaic virus (PlAMV) is a member of the genus Potexvirus and has an exceptionally wide host range. It causes severe damage to lilies. Here we report on the complete nucleotide sequences of two new Japanese PlAMV isolates, one from the eudicot weed Viola grypoceras (PlAMV-Vi), and the other from the eudicot shrub Nandina domestica Thunb. (PlAMV-NJ). Their genomes contain five open reading frames (ORFs), which is characteristic of potexviruses. Surprisingly, the isolates showed only 76.0-78.0 % sequence identity with each other and with other PlAMV isolates, including isolates from Japanese lily and American nandina. Amino acid alignments of the replicase coding region encoded by ORF1 showed that the regions between the methyltransferase and helicase domains were less conserved than other regions, with several insertions and/or deletions. Phylogenetic analyses of the full-length nucleotide sequences revealed a moderate correlation between phylogenetic clustering and the original host plants of the PlAMV isolates. This study revealed the presence of two highly divergent PlAMV isolates in Japan.

Control of Russet Crack Disease in Sweetpotato Plants Using a Protective Mild Strain of Sweet potato feathery mottle virus.

A mild isolate (designated as 10-O) of Sweet potato feathery mottle virus (SPFMV) was obtained from Ipomoea batatas. This isolate rarely caused skin discoloration and did not cause russet crack disease on the storage roots of I. batatas that are typical of infection with the severe strain of SPFMV (SPFMV-S). The yield of the 10-O-infected I. batatas ranged from 92 to 105% of the yield of healthy I. batatas. The coat protein gene of 10-O encodes 315 amino acids and has sequence identities of 91.1% at the nucleotide level and 95.6% at the amino acid level with the corresponding region of SPFMV-S. When I. batatas cuttings were inoculated with 10-O and later challenged with SPFMV-S, russet crack symptoms were much reduced and SPFMV-S was not detected in the challenged plants. These results indicate that 10-O can be an effective biological control agent against russet crack disease.

Molecular and Serological Characterization of Cucumber mottle virus, a New Cucurbit-Infecting Tobamo-like Virus.

A new tobamo-like virus was isolated from a greenhouse-grown cucumber that showed severe mosaic distortion on leaves and fruit, in the southern part of Japan. The virus was tentatively designated Cucumber mottle virus (CuMoV) and further characterized. The size and antigenicity of the coat protein (CP) and the complete sequence of the genome were compared with those of the known cucurbit-infecting tobamoviruses: the W and SH strains of Cucumber green mottle mosaic virus (CGMMV), the C and Y strains of Kyuri green mottle mosaic virus (KGMMV), Cucumber fruit mottle mosaic virus (CFMMV), and Zucchini green mottle mosaic virus (ZGMMV). The CP of CuMoV migrated more slowly than those of CGMMV-W and -SH and KGMMV-C and -Y in sodium dodecyl sulfate polyacrylamide gel electrophoresis. In Western blot analysis, the CP of CuMoV cross-reacted weakly with antisera against CGMMV-W and did not react with antisera against KGMMV-Y. The overall nucleotide sequence of CuMoV had 62.5 to 63.5% identity with those of CGMMV-W, -SH, KGMMV-Y, CFMMV, and ZGMMV. The genome organization was characteristic of tobamoviruses, encoding a 131-kb protein, a 188-kb protein, a movement protein (MP), and CP in 5' to 3' order. In the phylogenetic analyses of the CP, CuMoV was placed in a separate lineage from CGMMV-W, -SH, KGMMV-C, -Y, CFMMV, and ZGMMV. The results indicate that CuMoV is a distinct tobamovirus species which represents a third sub-subgroup in the cucurbit-infecting tobamoviruses.

Cryptic polyadenylation of transcripts of an RNA virus gene introduced into tobacco plants.

We constructed an expression vector for the coat protein (CP) gene and the 3' untranslated region (3' UTR) of RNA virus (sweet potato feathery mottle virus severe strain (SPFMV-S)) lacking a foreign terminator. Out of seven transgenic tobacco plants, expression of the transgene was observed in six plants. RT-PCR analysis revealed that the transcripts had a poly(A) tail, and in most of them, polyadenylation occurred on the 5' side of the 3' UTR. These results suggest that the viral sequence contains a cryptic polyadenylation signal that permits 3'-end processing of the transcripts.