Cap-snatching as a possible contributor to photosynthesis shut-off

Cap-snatching is a mechanism applied by segmented, negative strand (-) RNA viruses (NSVs) to initiate genome transcription. So far, the cap donor source of cytoplasmic-replicating NSVs has remained elusive. Recently, studies pointed to processing body (P body, PB) as the potential source for providing capped RNAs but conclusive evidence is still lacking. To attempt identify-ing these sources, here the 5' non -viral leader sequences of Tomato spotted wilt virus (TSWV) N mRNAs were analysed by high -throughput sequencing (HTS) from plants subjected to normal and heat-stress conditions, and subsequently mapped on host donor transcripts. The majority of non -viral heterogenous, host-derived leader sequences ranged in size between similar to 10-20 nt and contained A or AG residues at the cleavage site and the presence of certain sequence motifs. Mapping the capped-leader sequences to the 5' UTR region of genes encoded by the Nicotiana tabacum genome, identified 348 donor genes and which were specifically enriched in cellular photosynthesis pathway. Nineteen of those were clearly expressed differentially at normal condition versus heat-stress conditions. Although the results did not point towards snatching of capped -RNA leader sequences from certain cytoplasmic RNA granules in particular, they indicated photosynthesis downregulation (and development of disease symptoms) partially result from cap-snatching.

Automated summary

Cap-snatching is a mechanism used by NSVs to initiate genome transcription, with the cap donor source still remaining elusive. Studies suggest that processing bodies may be a potential source for capped RNAs, but conclusive evidence is lacking. Experimental results indicate that downregulation of photosynthesis is partially due to cap-snatching.