Ichiro Fujisawa

Replication of Tomato spotted wilt virus After Ingestion by Adult Thrips setosus is Restricted to Midgut Epithelial Cells

ABSTRACT If acquisition access feeding (AAF) is first given after adult eclosion, none of the nine thrips species able to serve as tospovirus vectors can become infective. The previous cellular investigations of this phenomenon, carried out only in Frankliniella occidentalis, suggested that infectivity was prevented because the type member of the tospoviruses, Tomato spotted wilt virus (TSWV), was unable to enter the midgut of adult thrips. The present study extends a cellular view of tospovirus-thrips interactions to a species other than the western flower thrips, F. occidentalis. Our findings show that TSWV enters and replicates within the midgut of adult Thrips setosus, but does not infect cells beyond the midgut epithelia. After AAF as adult, TSWV replicated in T. setosus midgut cells as indicated by significant increases in nucleocapsid (N) protein detected by double-antibody sandwich enzyme-linked immunosorbent assay, and the presence of inclusions containing the S RNA-encoded nonstructural and N proteins revealed by microscopic observations. Electron microscopic observations of adult insects showed that no infection occurred in cells beyond the midgut epithelia, and insects subsampled from the same cohorts could not transmit TSWV. In contrast, electron microscopy observations of larval T. setosus revealed that TSWV infected the midgut and muscle cells, and adult insects developing from these cohorts had infected salivary glands and were able to transmit TSWV. Mature virions were observed only in the salivary glands of adults developing from infected larvae. Our findings suggest that the barrier to infectivity in T. setosus adults differs from that shown for F. occidentalis adults.

Characterization of Grapevine Algerian latent virus isolated from nipplefruit (Solanum mammosum) in Japan.

Alfalfa mosaic virus (AMV), Cucumber mosaic virus (CMV), Potato virus Y (PVY), Tomato bushy stunt virus nipplefruit strain (TBSV-Nf), and an unknown spherical virus were isolated from nipplefruit (Solanum mammosum) cultivated in Chiba Prefecture, Japan. The spherical virus was identified as Grapevine Algerian latent virus nipplefruit strain (GALV-Nf) from the genus Tombusvirus, based on its physical properties, serological relationships, and analysis of genomic RNA. The genomic RNA of GALV-Nf is 4731 nucleotides long and encodes five open reading frames as well as those of other tombusviruses. Nipplefruit infected with GALV-Nf had severe stunting, leaf deformation, and clear mosaic symptoms. This is the first report of an isolation of GALV in Japan.

Characterization of Tomato bushy stunt virus newly isolated from nipplefruit (Solanum mammosum) in Japan.

Tomato bushy stunt virus (TBSV) was isolated from nipplefruit (Solanum mammosum) in Chiba Prefecture, Japan, with mosaic symptoms, leaf deformation, and stunting. The genomic structure of the TBSV-nipplefruit strain (TBSV-Nf) is identical to that of the TBSV-cherry strain (TBSV-Ch). Transcripts from its full-length cDNA clone without a cap analog at the 5′ terminus infected Nicotiana glutinosa, Nicotiana benthamiana, S. mammosum, Lycopersicon esculentum, Chenopodium amaranticolor, and Chenopodium quinoa, which displayed symptoms identical to those of the parental virus. Although TBSV-Ch systemically infected nipplefruit, systemic symptoms caused by TBSV-Nf were more severe than those by TBSV-Ch. This virus is the first TBSV discovered in Japan and the first TBSV ever isolated from nipplefruit.