In Situ Localization and Tissue Distribution of the Replication-Associated Proteins of Cucumber Mosaic Virus in Tobacco and Cucumber

Abstract

The replication-associated proteins encoded by Cucumber mosaic virus (CMV), the 1a and 2a proteins, were detected by immunogold labeling in two host species of this virus, tobacco (Nicotiana tabacum) and cucumber (Cucumis sativus). In both hosts, the 1a and 2a proteins colocalized predominantly to the vacuolar membranes, the tonoplast. While plus-strand CMV RNAs were found distributed throughout the cytoplasm by in situ hybridization, minus-strand CMV RNAs were barely detectable but were found associated with the tonoplast. In both cucumber and tobacco, 2a protein was detected at higher densities than 1a protein. The 1a and 2a proteins also showed quantitative differences with regard to tissue distributions in tobacco and cucumber. About three times as much 2a protein was detected in CMV-infected cucumber tissues as in CMV-infected tobacco tissues. In tobacco, high densities of these proteins were observed only in vascular bundle cells of minor veins. In contrast, in cucumber, high densities of 1a and 2a proteins were observed in mesophyll cells, followed by epidermis cells, with only low levels being observed in vascular bundle cells. Differences were also observed in the distributions of 2a protein and capsid protein in vascular bundle cells of the two host species. These observations may represent differences in the relative rates of tissue infection in different hosts or differences in the extent of virus replication in vascular tissues of different hosts.

Differential Subnuclear Localization of RNA Strands of Opposite Polarity Derived from an Autonomously Replicating Viroid[W]

“…Immediately after synthesis and processing, the genomic but not the antigenomic Hepatitis delta virus RNAs are exported out of the nucleus in infected human hepatoma cultured cells . In an infected tobacco and cucumber cell, the Cucumber mosaic virus (ϩ)-strand RNA is localized throughout the cytoplasm, whereas the (Ϫ)-strand RNA is localized predominantly to the tonoplast (Cillo et al, 2002). Although the role of virusencoded proteins in the differential subcellular localization of viral RNAs of opposite polarity remains to be elucidated, it is possible that cellular factors also are involved.…”

Molecular Population Genetics of Cucumber Mosaic Virus in California: Evidence for Founder Effects and Reassortment

“…The 2b protein is related to long-distance movement and virulence and is a suppressor of RNA silencing (3,13). Unlike the conserved 1a-membrane, MP-plasmodesma, and CP-RNA and -aphid vector interactions (11,29), the 2b-host interaction has been suggested to be host specific. The fact that the 2b protein is essential for long-distance virus movement within cucumber plants but not for systemic spread in Nicotiana spp.…”

Arabidopsis tonoplast proteins TIP1 and TIP2 interact with the cucumber mosaic virus 1a replication protein

“…However, the wide variety of intracellular membrane compartments employed by different positive-strand RNA viruses, as well as the variance inherent in their specific targeting behaviour, indicates that individual viruses may require unique host factors which are associated with specific intracellular membranes (Tereba & Lai, 1982). Despite these expectations, specific information regarding such host factors is currently limited to only a few examples.Cucumber mosaic virus (CMV) replication occurs in association with the vacuolar membrane, also known as the tonoplast (Cillo et al, 2002). Protein 1a, encoded by RNA 1, has a putative methyltransferase domain and helicase domain, and has been recognized as a component of the isolated CMV replicase (Hayes & Buck, 1990).…”

“…Protein 1a, encoded by RNA 1, has a putative methyltransferase domain and helicase domain, and has been recognized as a component of the isolated CMV replicase (Hayes & Buck, 1990). It colocalizes to the tonoplast with protein 2a which harbours an RNA-dependent RNA polymerase motif (Cillo et al, 2002).The tobamovirus multiplication 1 (TOM1) protein and its homologues TOM3 and TOM2A are required for the efficient replication of Tobacco mosaic virus (TMV), but not for the multiplication of either CMV or Turnip crinkle virus in Arabidopsis. They are transmembrane proteins localized in the tonoplast, which interact with TMV virus replication factors, as well as with each other (Tsujimoto et al, 2003;Yamanaka et al, 2002).…”

“…Cucumber mosaic virus (CMV) replication occurs in association with the vacuolar membrane, also known as the tonoplast (Cillo et al, 2002). Protein 1a, encoded by RNA 1, has a putative methyltransferase domain and helicase domain, and has been recognized as a component of the isolated CMV replicase (Hayes & Buck, 1990).…”