Trans-acting small interfering RNAs (ta-siRNAs) are a class of endogenous small RNA, associated with posttranscriptional gene silencing. Their biogenesis requires an initial microRNA (miRNA)-mediated cleavage of precursor RNA. Around 20 different ta-siRNA-producing loci (TASs), whose sequences are conserved, are reported in plants. In tomato, two TAS gene families have been identified, which are found to target auxin response factor gene and bacterial spot disease resistance protein Bs4 gene. Using high-throughput computational and experimental approach, we identified a new locus-producing ta-siRNA in tomato. We have also identified the putative miRNA regulating the production of ta-siRNA from this locus. The ta-siRNAs generated from TAS4 were up-regulated upon infection with a DNA virus. The potential targets of ta-siRNAs were predicted to be variety of proteins including MYB transcription factors and cell cycle regulators for some of the ta-siRNAs produced.

The two biological evidences to endorse the antiviral activity of RNA interference (RNAi) are biogenesis ofviral-siRNA (v-siRNA) by the host and encoding of RNAi-suppressor protein by viral genome. It has beenrecently established that mammals and mammalian cell lines mount antiviral RNAi to defend themselvesagainst the invading viruses. The large part of viral pathogenicity is also due to the RNAi suppressor proteins.In this context it is only natural to ask what kinds of RNAi suppressors are encoded by the Severe AcuteRespiratory Syndrome Coronavirus 2 (SARS-CoV-2), the central character of the present pandemic. Thefollowing mini review addresses this question.