Search

The L11Y strain of Tomato mosaic virus (ToMV) causes severe chlorosis on infected tobacco leaves. Sequencing analysis for the genome showed that L11Y contained multiple nucleotide changes and that some led to amino acid substitutions, when compared with that of the common L strain of ToMV. The chimeric virus, which has the CP of L11Y in the context of the L strain RNA genome, caused severe chlorosis on infected tobacco plants, suggesting that the CP of L11Y containing three amino acid changes (E33S, A86T and E97K) was the determinant of the chlorosis. Two of these amino acid changes (A86T and E97K) were associated with the induction of chlorosis when present together in the CP. Severe destruction and deformation of chloroplasts and the formation of discrete dark-staining materials adjacent to chloroplasts were observed with electron microscopy in L11Y-infected plants. Fewer virus particles accumulated in the cytoplasm of L11Y-infected plant cells. The level of accumulation of CP subgenomic RNA and CP in the infected protoplasts was similar between L and L11Y. Fewer virus particles accumulated in L11Y-infected protoplasts, and many of them were shorter-than-full-length. [ABSTRACT FROM AUTHOR]

The tomato Tm-1 gene confers resistance to tomato mosaic virus (ToMV). Here, we report that the extracts of Tm-1 tomato cells (GCR237) have properties that inhibit the in vitro RNA replication of WT ToMV more strongly than that of the Tm-1-resistance-breaking mutant of ToMV, LT1. We purified this inhibitory activity and identified a polypeptide of ≈80 kDa (p80GCR237) using LC-tandem MS. The amino acid sequence of p80GCR237 had no similarity to any characterized proteins. The p80GCR237 gene cosegregated with Tm-1; transgenic expression of p80GCR237 conferred resistance to ToMV within tomato plants; and the knockdown of p80GCR237 sensitized Tm-1 tomato plants to ToMV, indicating that Tm-1 encodes p80GCR237 itself. We further show that in vitro-synthesized Tm-1 (p80GCR237) protein binds to the replication proteins of WT ToMV and inhibits their function at a step before, but not after, the viral replication complex is formed on the membrane surfaces. Such binding was not observed for the replication proteins of LT1. These results suggest that Tm-1 (p80GCR237) inhibits the replication of WT ToMV RNA through binding to the replication proteins. [ABSTRACT FROM AUTHOR]

Abstract: The Tm-2 gene of tomato and its allelic gene, Tm-2 2 , confer resistance to Tomato mosaic virus (ToMV) and encode a member of the coiled-coil/nucleotide binding-ARC/leucine-rich repeat (LRR) protein class of plant resistance (R) genes. Despite exhibiting only four amino acid differences between the products of Tm-2 and Tm-2 2 , Tm-2 2 confers resistance to ToMV mutant B7, whereas Tm-2 is broken by ToMV-B7. An Agrobacterium-mediated transient expression system was used to study the mechanism of differential recognition of the movement proteins (MPs), an avirulence factor for ToMV resistance, of ToMV-B7 by Tm-2 and Tm-22. Although resistance induced by Tm-2 and Tm-2 2 is not usually accompanied by hypersensitive response (HR), Tm-2 and Tm-2 2 induced HR-like cell death by co-expression with MP of a wild-type ToMV, a strain that causes resistance for these R genes, and Tm-2 2 but not Tm-2 induced cell death with B7-MP in this system. Site-directed amino acid mutagenesis revealed that Tyr-767 in the LRR of Tm-22 is required for the specific recognition of the B7-MP. These results suggest that the Tyr residue in LRR contributes to the recognition of B7-MP, and that Tm-2 and Tm-2 2 are involved in HR cell death. [Copyright &y& Elsevier]

Pepper mild mottle virus (PMM0V) infects pepper plants, causing mosaic symptoms on the upper developing leaves. We investigated the relationship between a virus pathogenicity determinant domain and the appearance of mosaic symptoms. Genetically modified PMMoV mutants were constructed, which had a base substitution in the 130K replication protein gene causing an amino acid change or a truncation of the 3߰ terminal pseudoknot structure. Only one substitution mutant (at amino acid residue 349) failed to cause symptoms, although its accumulation was relatively high. Conversely, the pseudoknot mutants showed the lower accumulation, but they still caused mosaic symptoms as severe as the wild-type virus. Therefore, the level of virus accumulation in a plant does not necessarily correlate with the development of mosaic symptoms. The activity to suppress posttranscriptional gene silencing (PIGS) was impaired in the asymptomatic mutant. Consequently, pathogenicity causing mosaic symptoms should be controlled by combat between host PTGS and its suppression by the 130K replication protein rather than virus accumulation. [ABSTRACT FROM AUTHOR]