The Sw5a gene confers resistance to ToLCNDV and triggers an HR response after direct AC4 effector recognition

Several attempts have been made to identify antiviral genes against Tomato leaf curl New Delhi virus (ToLCNDV) and related viruses. This has led to the recognition of Ty genes (Ty1-Ty6), which have been successful in developing virus-resistant crops to some extent. Owing to the regular appearance of resistance-breaking strains of these viruses, it is important to identify genes related to resistance. In the present study, we identified a ToLCNDV resistance (R) gene, SlSw5a, in a ToLCNDV-resistant tomato cultivar, H-88-78-1, which lacks the known Ty genes. The expression of SlSw5a is controlled by the transcription factor SlMyb33, which in turn is regulated by microRNA159 (sly-miR159). Virus-induced gene silencing of either SlSw5a or SlMyb33 severely increases the disease symptoms and viral titer in leaves of resistant cultivar. Moreover, in SlMyb33-silenced plants, the relative messenger RNA level of SlSw5a was reduced, suggesting SlSw5a is downstream of the sly-miR159-SlMyb33 module. We also demonstrate that SlSw5a interacts physically with ToLCNDV-AC4 (viral suppressor of RNA silencing) to trigger a hypersensitive response (HR) and generate reactive oxygen species at infection sites to limit the spread of the virus. The “RTSK” motif in the AC4 C terminus is important for the interaction, and its mutation completely abolishes the interaction with Sw5a and HR elicitation. Overall, our research reports an R gene against ToLCNDV and establishes a connection between the upstream miR159-Myb33 module and its downstream target Sw5a to activate HR in the tomato, resulting in geminivirus resistance.

Constrained Peptides Mimic a Viral Suppressor of RNA Silencing

The structure-based design of constrained alpha-helical peptides derived from the viral suppressor of RNA silencing TAV2b is described. We observe that the introduction of two inter-side chain crosslinks provides peptides with increased alpha-helicity and protease stability. One of these modified peptides (B3) shows high affinity for different double-stranded RNA structures including a palindromic siRNA as well as microRNA-21 and its precursor pre-miR-21. Notably, B3 binding to pre-miR-21 inhibits Dicer processing in a biochemical assay. As a further characteristic this peptide also exhibits cellular entry. <br>

Constrained Peptides Mimic a Viral Suppressor of RNA Silencing

The structure-based design of constrained alpha-helical peptides derived from the viral suppressor of RNA silencing TAV2b is described. We observe that the introduction of two inter-side chain crosslinks provides peptides with increased alpha-helicity and protease stability. One of these modified peptides (B3) shows high affinity for different double-stranded RNA structures including a palindromic siRNA as well as microRNA-21 and its precursor pre-miR-21. Notably, B3 binding to pre-miR-21 inhibits Dicer processing in a biochemical assay. As a further characteristic this peptide also exhibits cellular entry. <br>

Effect of RNA silencing suppression activity of chrysanthemum virus B p12 protein on small RNA species

Chrysanthemum virus B encodes a multifunctional p12 protein that acts as a transcriptional activator in the nucleus and as a suppressor of RNA silencing in the cytoplasm. Here, we investigated the impact of p12 on accumulation of major classes of small RNAs (sRNAs). The results show dramatic changes in the sRNA profiles characterised by an overall reduction in sRNA accumulation, changes in the pattern of size distribution of canonical siRNAs and in the ratio between sense and antisense strands, lower abundance of siRNAs with a U residue at the 5′-terminus, and changes in the expression of certain miRNAs, most of which were downregulated.

Interaction of dengue NS3 with human RNA silencing machinery through HSPA1A

Viruses encode multiple proteins that interact with different host factors to aid in their establishment inside the host. Viral Suppressor of RNA silencing (VSR) are one such class of proteins that have been shown to interact with components of host machinery involved in post transcriptional gene silencing, a known antiviral defence mechanism. In the present study, we showed that dengue NS3, a known VSR not only interacts with HSPA1A, a cellular chaperone, but also modulates its expression levels. Further, we revealed HSPA1A associated with host RNA silencing machinery through its interaction with Argonaute proteins; Ago1, Ago2 and co-localizes with them in the cytoplasm of the cell. Together, these results provide evidence for involvement of other host partners in mediating VSR function of dengue NS3 and aid in deeper understanding of mechanisms underlying viral suppression of RNA silencing.