The complete genome sequence of a Slovak SL-1 isolate of Tomato mosaic virus (ToMV) was determined from the next generation sequencing (NGS) data, further confirming a limited sequence divergence in this tobamovirus species. Tomato genotypes Monalbo, Mobaci and Moperou, respectively carrying the susceptible tm-2 allele or the Tm-1 and Tm-2 resistant alleles, were tested for their susceptibility to ToMV SL-1. Although the three tomato genotypes accumulated ToMV SL-1 to similar amounts as judged by semi-quantitative DAS-ELISA, they showed variations in the rate of infection and symptomatology. Possible differences in the intra-isolate variability and polymorphism between viral populations propagating in these tomato genotypes were evaluated by analysis of the capsid protein (CP) encoding region. Irrespective of genotype infected, the intra-isolate haplotype structure showed the presence of the same highly dominant CP sequence and the low level of population diversity (0.08–0.19%). Our results suggest that ToMV CP encoding sequence is relatively stable in the viral population during its replication in vivo and provides further demonstration that RNA viruses may show high sequence stability, probably as a result of purifying selection.

Summary. -Viruses use both material and energy sources of their hosts and redirect the production of disposable compounds in order to make viral replication more effi cient. Metabolism of infected organisms is modifi ed by these enhanced requirements as well by their own defense response. Resulting complex story consists of many regulation events on various gene expression levels. Elucidating these processes may contribute to the knowledge on virus-host interactions and to evolving new antiviral strategies. In our work we applied a subtractive cloning technique to compare the transcriptomes of healthy and plum pox virus (PPV)-infected Nicotiana benthamiana plants. Several genes were found to be induced or repressed by the PPV infection. Th e induced genes were mainly related to general stress response or photosynthesis, several repressed genes could be connected with growth defects evoked by the infection. Interestingly, some genes usually up-regulated by fungal or bacterial infection were found repressed in PPV-infected plants. Potential involvement of particular diff erently expressed genes in the process of PPV infection is discussed.Keywords: virus-host interaction; gene expression; subtractive hybridization * Corresponding author. E-mail: virusubr@savba.sk; phone: +421-2-59302447. Abbreviations: APX = ascorbate peroxidase; CAB = chlorophyll a/b-binding protein; DSPP = dentin sialophosphoprotein; FRL = Frigida-like protein; GCS = glycine cleavage system; HMGB = high mobility group B protein; JA = jasmonic acid; MLP = major latex protein; MT = metallothionein; PI-PLC = phosphoinositide-specifi c phospholipase C; PPV = plum pox virus; PRG = photosynthesis-related gene; PS II = photosystem II; ROS = reactive oxygen species; SNS = S-norcoclaurine synthase; SUMO = small ubiquitin-related modifi er; TLP = tetraspanin-like protein; Ub = ubiquitin

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The P1 protein is derived from the N terminus of potyvirus-coded polyprotein. In addition to the proteolytic activity essential for its maturation, it probably participates in suppression of host defense and/or in virus replication. Clear validation of the P1 in vivo function(s), however, is not yet available. We applied an infectious cDNA clone of plum pox virus (PPV), where the P1 was N-fused with a hexahistidine tag, to trace this protein in Nicotiana benthamiana plants during the PPV infection. Immunoblot analysis with the anti-his antibody showed a diffuse band corresponding to the molecular weight about 70-80 kDa (about twice larger than expected) in the root samples from early stage of infection. This signal culminated on the sixth day post inoculation, later it rapidly disappeared. Sample denaturation by boiling in SDS before centrifugal clarification was essential, indicating strong affinity of P1-his to some plant compound sedimenting with the tissue and cell debris.