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A series of novel pyrimidine-based derivative compounds were synthesized and evaluated for antiviral activity against Tobacco mosaic virus (TMV). All chemical structures of the prepared compounds were identified and characterized by IR, NMR, and elemental analysis. Under greenhouse conditions, the preliminary bioassays revealed that all compounds exhibited anti-TMV activity ranging from 23.5 % to 90.1% at 50 µg/mL concentration, indicating potential antiviral efficacy. Among the new compounds, the benzylidene derivative 3a was the most potent and demonstrated the highest inhibition effect of 90%, with a significant reduction in the TMV accumulation level of 91.4%. Furthermore, the curative activity of 3a was associated with a considerable decrease in H2O2 and MDA (nonenzymatic oxidative stress markers) compared to the TMV treatment. In addition, significant increases in the transcriptional levels of pathogenesis-related proteins (PR-1, PR-3, PR-4, and PR-5) at 4 and 6 dpi were shown to induce systemic resistance against TMV. Furthermore, molecular docking investigation demonstrated that the benzylidene derivative 3a was strongly lodged in the binding sites of TMV-coat protein at position 2. Consequently, the obtained results suggest that the new 3a compound could be applied as a safe control agent against plant viral infection.

Tobacco mosaic virus (TMV) causes severe damage and economic losses of tomato in crop yield production and quality worldwide. Tomato plants infected with TMV usually show a mosaic pattern and chlorosis symptoms that result from affected chloroplasts. To elucidate tomato–TMV interactions, the transcriptional profiles of tomato tissues at different time intervals were analysed using a differential display-polymerase chain reaction technique. Compared to mock-inoculated plants, and based on gene expression changes in tomato plants, the representative down- and up-regulated genes were selected for further analysis. The Basic Local Alignment Search Tool at the National Center for Biotechnology Information (NCBI-BLAST) analysis revealed that the three up-regulated gene transcripts at 15 days post-inoculation were coding for chloroplast (MG565980 and MG565979) and kinesin-like proteins (MG565981). Additionally, the down-regulated gene was a chloroplast-related gene (MG565978). Interestingly, the two chloroplast genes, MG565978 and MG565980, shared more than 96% sequence identity, and their transmembrane profiles were nearly identical. On the other hand, many protein kinase C phosphorylation, casein kinase II phosphorylation and N-myristoylation sites were detected within the MG565981 gene. Moreover, the high similarity between the kinesin gene and many Arabidopsis defensin genes indicated that it might play an important role in the plant defence system against TMV infection. It should be stressed that studies of the pathways in which chloroplast and kinesin-like protein genes are involved may elucidate the mechanisms of tomato tolerance to viral infection and can lead us to a more comprehensive understanding of tomato–TMV interactions.