Function of the 30 kd protein of tobacco mosaic virus: involvement in cell-to-cell movement and dispensability for replication

Abstract

We have investigated the function of the 30 kd protein of tobacco mosaic virus (TMV) by a reverse genetics approach. First, a point mutation of TMV Ls1 (a temperature‐sensitive mutant defective in cell‐to‐cell movement), that causes an amino acid substitution in the 30 kd protein, was introduced into the parent strain, TMV L. The generated mutant showed the same phenotype as TMV Ls1, and therefore the one‐base substitution in the 30 kd protein gene adequately explains the defectiveness of TMV Ls1. Next, four kinds of frame‐shift mutants were constructed, whose mutations are located at three different positions of the 30 kd protein gene. All the frame‐shift mutants were replication‐competent in protoplasts but none showed infectivity on tobacco plants. From these observations the 30 kd protein was confirmed to be involved in cell‐to‐cell movement. To clarify that the 30 kd protein is not necessary for replication, two kinds of deletion mutants were constructed; one lacking most of the 30 kd protein gene and the other lacking both the 30 kd and coat protein genes. Both mutants replicated in protoplasts and the former still produced the subgenomic mRNA for the coat protein. These results clearly showed that the 30 kd protein, as well as the coat protein, is dispensable for replication and that no cis‐acting element for replication is located in their coding sequences. It is also suggested that the signal for coat protein mRNA synthesis may be located within about 100 nucleotides upstream of the initiation codon of the coat protein gene.

Cell-to-cell Transport of Cowpea Mosaic Virus Requires Both the 58K/48K Proteins and the Capsid Proteins

“…With respect to the 58K and 48K proteins, this result was not unexpected. These proteins show a limited homology with the 30K transport protein of tobamoviruses (Meyer et al, 1986;Deom et al, 1987;Meshi et al, 1987). Furthermore the 48K protein is found in the membrane fraction of infected leaves (Wellink et al, 1987) and recent results with immunogold labelling of sections of infected leaves with anti-48K serum have revealed an association of this protein with tubular structures protruding from the cell wall (J. van Lent, unpublished results).…”

Nucleotide Sequence of the Genomic RNA of Pepper Mild Mottle Virus, a Resistance-breaking Tobamovirus in Pepper

“…The 30K proteins of tobamoviruses are responsible for cell-to-cell spread of the viral infection (Deom et al, 1987;Meshi et al, 1987), by modifying the plasmodesmata (Wolf et al, 1989). Although the exact mechanism of action is unknown (Hull, 1989), a domain responsible for binding to nucleic acids which maps between amino acid positions 65 and 87 has been defined (Citovsky et al, 1990).…”

“…The tobamoviral RNA encodes four different proteins: 126K, 183K, 30K and 17.5K, in that order. The 126K and 183K proteins are involved in the replication processes (Young et al, 1987;Quadt & Jaspars, 1989), the 30K protein participates in the cell-to-cell spread of the virus (Deom et al, 1987;Meshi et al, 1987) and the 17-5K protein is the coat protein. The 126K and 183K proteins are directly translated from the viral RNA, whereas the 30K protein and coat protein are translated from subgenomic RNAs (Palukaitis & Zaitlin, 1986).…”

Detection and identification of TMV infecting tomato under protected cultivation in Paraná State

“…The genome of TMV encodes at least four proteins (Goelet et al, 1982). The 3' proximal genes encode a 30-kDa cell-tocell movement protein, also called P30 protein, and a 17.5-kDa coat protein (Meshi et al, 1987, Citovsky et al, 1992. There are reports about Tobamovirus infection in tomato, mainly from São Paulo, Minas Gerais, and Federal District (Resende and Cupertino, 1996).…”