Résumé
Tobamoviruses encode a silencing suppressor that binds small RNA (sRNA) duplexes
in vitro and supposedly in vivo to
counteract antiviral silencing. Here, we used sRNA deep-sequencing combined with
transcriptome profiling to determine the global impact of tobamovirus infection
on Arabidopsis sRNAs and their mRNA targets. We found that
infection of Arabidopsis plants with Oilseed rape
mosaic tobamovirus causes a global size-specific enrichment of
miRNAs, ta-siRNAs, and other phased siRNAs. The observed patterns of sRNA
enrichment suggest that in addition to a role of the viral silencing suppressor,
the stabilization of sRNAs might also occur through association with unknown
host effector complexes induced upon infection. Indeed, sRNA enrichment concerns
primarily 21-nucleotide RNAs with a 5′-terminal guanine. Interestingly,
ORMV infection also leads to accumulation of novel miRNA-like sRNAs from miRNA
precursors. Thus, in addition to canonical miRNAs and miRNA*s, miRNA
precursors can encode additional sRNAs that may be functional under specific
conditions like pathogen infection. Virus-induced sRNA enrichment does not
correlate with defects in miRNA-dependent ta-siRNA biogenesis nor with global
changes in the levels of mRNA and ta-siRNA targets suggesting that the enriched
sRNAs may not be able to significantly contribute to the normal activity of
pre-loaded RISC complexes. We conclude that tobamovirus infection induces the
stabilization of a specific sRNA pool by yet unknown effector complexes. These
complexes may sequester viral and host sRNAs to engage them in yet unknown
mechanisms involved in plant:virus interactions.