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Mlotshwa, Sizolwenkosi; Verver, J.; Sithole-Niang, Idah; Gopinath, K.; Carette, Jan E.; Kammen, A. van; Wellink, J.

doi:10.1023/a:1020122104651

Cited by 20 publications

(6 citation statements)

References 38 publications

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“…Unlike HC-Pro, which is a cytoplasmic protein and binds to siRNA duplex [63], βC1 of TYLCCNB primarily localizes in nuclei and binds to single- but not double-stranded RNA [41], [64]. It is unclear how structurally unrelated HC-Pro and βC1 have evolved independently to induce rgs-CaM .…”

Section: Discussionmentioning

confidence: 99%

Suppression of RNA Silencing by a Plant DNA Virus Satellite Requires a Host Calmodulin-Like Protein to Repress RDR6 Expression

et al. 2014

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In plants, RNA silencing plays a key role in antiviral defense. To counteract host defense, plant viruses encode viral suppressors of RNA silencing (VSRs) that target different effector molecules in the RNA silencing pathway. Evidence has shown that plants also encode endogenous suppressors of RNA silencing (ESRs) that function in proper regulation of RNA silencing. The possibility that these cellular proteins can be subverted by viruses to thwart host defense is intriguing but has not been fully explored. Here we report that the Nicotiana benthamiana calmodulin-like protein Nbrgs-CaM is required for the functions of the VSR βC1, the sole protein encoded by the DNA satellite associated with the geminivirus Tomato yellow leaf curl China virus (TYLCCNV). Nbrgs-CaM expression is up-regulated by the βC1. Transgenic plants over-expressing Nbrgs-CaM displayed developmental abnormities reminiscent of βC1-associated morphological alterations. Nbrgs-CaM suppressed RNA silencing in an Agrobacterium infiltration assay and, when over-expressed, blocked TYLCCNV-induced gene silencing. Genetic evidence showed that Nbrgs-CaM mediated the βC1 functions in silencing suppression and symptom modulation, and was required for efficient virus infection. Moreover, the tobacco and tomato orthologs of Nbrgs-CaM also possessed ESR activity, and were induced by betasatellite to promote virus infection in these Solanaceae hosts. We further demonstrated that βC1-induced Nbrgs-CaM suppressed the production of secondary siRNAs, likely through repressing RNA-DEPENDENT RNA POLYMERASE 6 (RDR6) expression. RDR6-deficient N. benthamiana plants were defective in antiviral response and were hypersensitive to TYLCCNV infection. More significantly, TYLCCNV could overcome host range restrictions to infect Arabidopsis thaliana when the plants carried a RDR6 mutation. These findings demonstrate a distinct mechanism of VSR for suppressing PTGS through usurpation of a host ESR, and highlight an essential role for RDR6 in RNA silencing defense response against geminivirus infection.

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Section: Discussionmentioning

confidence: 99%

Suppression of RNA Silencing by a Plant DNA Virus Satellite Requires a Host Calmodulin-Like Protein to Repress RDR6 Expression

et al. 2014

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“…One puzzle raised by the observation that HC-Pro, which is a cytoplasmic protein [60],[61], interacts with a host transcription factor is: How and where do the two proteins have the opportunity to meet? Although HC-Pro has been shown to accumulate in nuclear inclusions in certain potyviral infections, it is thought that such inclusions represent storage of excess protein [61].…”

Section: Discussionmentioning

confidence: 99%

Two Plant Viral Suppressors of Silencing Require the Ethylene-Inducible Host Transcription Factor RAV2 to Block RNA Silencing

et al. 2010

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RNA silencing is a highly conserved pathway in the network of interconnected defense responses that are activated during viral infection. As a counter-defense, many plant viruses encode proteins that block silencing, often also interfering with endogenous small RNA pathways. However, the mechanism of action of viral suppressors is not well understood and the role of host factors in the process is just beginning to emerge. Here we report that the ethylene-inducible transcription factor RAV2 is required for suppression of RNA silencing by two unrelated plant viral proteins, potyvirus HC-Pro and carmovirus P38. Using a hairpin transgene silencing system, we find that both viral suppressors require RAV2 to block the activity of primary siRNAs, whereas suppression of transitive silencing is RAV2-independent. RAV2 is also required for many HC-Pro-mediated morphological anomalies in transgenic plants, but not for the associated defects in the microRNA pathway. Whole genome tiling microarray experiments demonstrate that expression of genes known to be required for silencing is unchanged in HC-Pro plants, whereas a striking number of genes involved in other biotic and abiotic stress responses are induced, many in a RAV2-dependent manner. Among the genes that require RAV2 for induction by HC-Pro are FRY1 and CML38, genes implicated as endogenous suppressors of silencing. These findings raise the intriguing possibility that HC-Pro-suppression of silencing is not caused by decreased expression of genes that are required for silencing, but instead, by induction of stress and defense responses, some components of which interfere with antiviral silencing. Furthermore, the observation that two unrelated viral suppressors require the activity of the same factor to block silencing suggests that RAV2 represents a control point that can be readily subverted by viruses to block antiviral silencing.

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“…However, viral siRNAs appear to be processed by different Dicer proteins (e.g., DCL2) (7), which may function mainly in the cytoplasm, where most plant viral RNA replicates. HC-Pro is known to be localized in the cytoplasm (32) and may therefore preferentially interfere with the methylation of the cytoplasmically processed viral smRNAs.…”

Section: Discussionmentioning

confidence: 99%

Extensive 3′ modification of plant small RNAs is modulated by helper component-proteinase expression

Ebhardt

Thi

Wang

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

137

109

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RNA silencing ͉ silencing suppressor ͉ cucumber mosaic virus ͉ Y-satellite P lants have three overlapping but distinct RNA silencing pathways that involve small interfering RNAs (siRNAs) and micro RNAs (miRNAs) (1). In the siRNA-related pathways, perfectly complementary dsRNAs are cleaved into siRNAs having two distinct size classes, 21-22 and 24 nt, by RNase III-type Dicer enzymes (2). These siRNAs are then incorporated into RNAinduced silencing complexes (RISCs) that guide the specific degradation of RNA in the cytoplasm (and possibly the nucleus) and͞or cytosine methylation of DNA in the nucleus (1, 3, 4). miRNAs are predominately 21-22 nt in length and are formed by the Dicer-mediated cleavage of hairpin-structured RNAs (5, 6). Both siRNAs and miRNAs play important roles in the control of spatial and temporal expression of key regulatory genes and can act through RISC-mediated mRNA cleavage (6, 7). The different pathways leading to the biogenesis of siRNAs and miRNAs in plants involve multiple protein factors that include the Dicer-like proteins (7, 8) and RNA-dependent RNA polymerases (9). A recent study has revealed that the 3Ј-terminal nucleotides of miRNAs in plants are methylated at their 2Ј or 3Ј hydroxyls by HEN1 (10), a protein previously shown to be required for the accumulation of miRNAs and sense transgene-derived siRNAs in Arabidopsis (11). It remains unclear, however, whether siRNAs are also methylated in plants, because HEN1 fails to methylate perfectly complementary duplex siRNAs in vitro (10).RNA silencing, and the siRNA pathway in particular, is a natural antiviral defense mechanism in plants (12). Consequently, many plant viruses encode proteins that can suppress RNA silencing by a variety of mechanisms. These silencing suppressors have become important tools in the elucidation of RNA silencing pathways in plants because they act differentially on the silencing machinery.

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Cited by 20 publications

References 38 publications

Suppression of RNA Silencing by a Plant DNA Virus Satellite Requires a Host Calmodulin-Like Protein to Repress RDR6 Expression

Suppression of RNA Silencing by a Plant DNA Virus Satellite Requires a Host Calmodulin-Like Protein to Repress RDR6 Expression

Two Plant Viral Suppressors of Silencing Require the Ethylene-Inducible Host Transcription Factor RAV2 to Block RNA Silencing

Extensive 3′ modification of plant small RNAs is modulated by helper component-proteinase expression

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