Project description:We investigated the role of A. thaliana RDRs in the RNAi-mediated viral immunity by using a mutant of cucumber mosaic virus (CMV) that does not express the VSR protein 2b. CMV contains three positive-strand genomic RNAs and the 2b protein encoded by RNA2 is essential for infection by suppressing antiviral silencing initiated by either DCL4 or DCL2. Our results demonstrate an essential role for the amplification of viral siRNAs by either RDR1 or RDR6 in antiviral silencing. Further analyses, including Illumina sequencing of more than 3.5 million viral siRNAs, indicated target specificity of the two antiviral RDRs.
Project description:We focused our analyses on the description of viral (CMV-?2b) and, based on genetic and molecular evidence, classified them and discussed their relevance in antiviral defense. Small RNAs from Arabidopsis plants from different genetic backgrounds infected with (CMV-?2b) were sequenced before or after immunoprecipitation with antibodies against key proteins involved in antiviral defense.
Project description:RNA silencing has an important role mediating sequence-specific virus resistance. Here, we analyzed in detail the interference of Cucumber Mosaic Virus (CMV) with the RNA silencing machinery of Arabidopsis thaliana. We detected that CMV infection induced the production of viral small interfering RNAs (vsiRNAs) that account for a significant part of the sRNome affecting the levels of other sRNA classes. Furthermore, we analyzed the incorporation of vsiRNAs into the main ARGONAUTE (AGO) proteins with a described antiviral role and the viral RNA silencing suppressor (VRS) 2b, by combining protein immunoprecipitation with sRNA high-throughput sequencing. vsiRNAs accumulated to high levels in AGO2, followed by AGO1, AGO5 and AGO7. Interestingly, vsiRNAs represented a significant percentage of AGO-loaded sRNAs and displaced other endogenous sRNAs. As a countermeasure, the VSR 2b loaded vsiRNAs and mRNA-derived siRNAs, which affected the expression of the genes they derived from. Additionally, we analyzed how vsiRNAs incorporated into the endogenous RNA silencing pathways by exploring their target mRNAs using parallel analysis of RNA end (PARE) sequencing. This strategy allowed us to identify 61 genes with degradome data supporting their vsiRNA-mediated cleavage. This work exemplifies the complex relationship of RNA viruses with the endogenous RNA silencing machinery and the multiple aspects of virus resistance and virulence that this interaction induces.