Functional comparison of RNA silencing suppressor between the p5 protein of rice grassy stunt virus and the p3 protein of rice stripe virus

Apr 4, 2015Virus research

Comparing how two rice viruses block RNA silencing using their p5 and p3 proteins

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Abstract

RGSVp5 may suppress post-transcriptional gene silencing similarly to RSVp3, but with different mechanisms.

RGSVp5 was shown to suppress sense transgene-mediated, inverted-repeat transgene-induced, and systemic silencing of GFP.
Unlike RSVp3, RGSVp5 did not bind to 21-, 22-, or 24-nucleotide small interfering RNA duplexes.
The subcellular localization of RGSVp5 was primarily in the cytoplasm, contrasting with the nuclear and cytoplasmic localization of RSVp3.
These findings suggest that while RGSVp5 acts as a viral suppressor of RNA silencing, its functional mechanism differs from that of RSVp3.

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Rice grassy stunt virus (RGSV) is a member of the genus Tenuivirus, which includes rice stripe virus (RSV), as the type species. A viral suppressor of RNA silencing (VSR) of RGSV has not been identified, whereas the p3 protein of RSV (RSVp3) encoded by the viral-sense (v) strand of RNA3 has been reported to act as a VSR. In this study, we examined the VSR function of the p5 protein of RGSV (RGSVp5), encoded by vRNA5. Expecting it to correspond to the vRNA3 of RSV, we compared the VSR function of RGSVp5 with that of RSVp3. In an Agrobacterium-mediated transient expression assay using a transgenic line of Nicotiana benthamiana that expressed green fluorescent protein and the wild type, RGSVp5 suppressed sense transgene-mediated post-transcriptional gene silencing (S-PTGS), inverted-repeat (IR) transgene-induced PTGS (IR-PTGS), and the systemic spread of GFP silencing, as in the case with RSVp3. By contrast, a gel mobility shift assay revealed that RGSVp5 did not have any distinct binding activity with 21-, 22-, or 24-nucleotide small interfering RNA (siRNA) duplexes, whereas RSVp3 binds to all three sizes of siRNA duplexes. Furthermore, the transiently expressed p5 protein fused with GFP was dispersed mainly in the cytoplasm, whereas the GFP-fused p3 protein of RSV was localized both in the nucleus and in the cytoplasm. Our results suggest that RGSVp5 functions as a VSR but that the suppression mechanism of RNA silencing and the subcellular localization of RGSVp5 differ from those of the analogous VSR, RSVp3, even in the same genus.

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Functional comparison of RNA silencing suppressor between the p5 protein of rice grassy stunt virus and the p3 protein of rice stripe virus

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