Tospoviruses are plant-infecting viruses belonging to the family Bunyaviridae. We used a collection of wild-type, phylogenetically distinct tomato spotted wilt virus isolates and related silencing-suppressor defective mutants to study the effects on the small RNA (sRNA) accumulation during infection of Nicotiana benthamiana. Our data showed that absence of a functional silencing suppressor determined a marked increase of the total amount of viral sRNAs (vsRNAs), and specifically of the 21 nt class. We observed a common under-representation of vsRNAs mapping to the intergenic region of S and M genomic segments, and preferential mapping of the reads against the viral sense open reading frames, with the exception of the NSs gene. The NSs-mutant strains showed enrichment of NSm-derived vsRNA compared to the expected amount based on gene size. Analysis of 5' terminal nucleotide preference evidenced a significant enrichment in U for the 21 nt- and in A for 24 nt-long endogenous sRNAs in all the samples. Hotspot analysis revealed a common abundant accumulation of reads at the 5' end of the L segment, mostly in the antiviral sense, for the NSs-defective isolates, suggesting that absence of the silencing suppressor can influence preferential targeting of the viral genome.
Keywords: RNA interference; Silencing suppressor; Tospovirus.
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