Antiviral RNA silencing suppression activity of Tomato spotted wilt virus NSs protein

Abstract

In addition to regulating gene expression, RNA silencing is an essential antiviral defense system in plants. Triggered by double-stranded RNA, silencing results in degradation or translational repression of target transcripts. Viruses are inducers and targets of RNA silencing. To condition susceptibility, most plant viruses encode silencing suppressors that interfere with this process, such as the Tomato spotted wilt virus (TSWV) NSs protein. The mechanism by which NSs suppresses RNA silencing and its role in viral infection and movement remain to be determined. We cloned NSs from the Hawaii isolate of TSWV and using two independent assays show for the first time that this protein restored pathogenicity and supported the formation of local infection foci by suppressor-deficient Turnip mosaic virus and Turnip crinkle virus. Demonstrating the suppression of RNA silencing directed against heterologous viruses establishes the foundation to determine the means used by NSs to block this antiviral process.

The bunyavirus nonstructural protein NSs suppresses plant immunity to facilitate its own transmission by improving vector insect performance

“…TSWV NSs is an avirulence determinant that triggers a hypersensitive response in resistant plants [46]. NSs is also a well-known viral suppressor of host RNA interference in both plants and insects and is essential for TSWV transmission by WFT [5,11,13]. Here, we identified NSs as a viral effector that attenuates the host defense system by suppressing MYC proteins (Fig 4B).…”

“…NSs suppresses host antiviral RNA silencing to promote TSWV infection [11]. To determine if the effect of NSs on manipulating vector behavior is dependent on its silencing suppressor activity, we explored the activity of NSs protein with an S48A/R51A mutation (mNSs) that destroys its silencing suppressor activity via RT-qPCR analysis and a WFT two-choice assay [24].…”

“…The negative-polarity S RNA encodes the major structural N protein on the complementary RNA strand of the virus, and in certain members of Orthobunyavirus and Orthohantavirus , the S RNA encodes an additional non-structural protein (NSs) via an overlapping reading frame. The NSs proteins of many bunyaviruses modulate host innate immune responses, and NSs in Orthotospovirus functions as a silencing suppressor in both plants and insects [11,12]. These proteins are responsible for establishing systemic infection in plants and for vial transmission by insect vectors [5,13].…”

Tomato Spotted Wilt Virus NSs Protein Supports Infection and Systemic Movement of a Potyvirus and Is a Symptom Determinant

“…In plants, nematodes, and insects, gene silencing is additionally an inducible, adaptable, specific, potent, and essential defense system against virus infection (antiviral RNA silencing) [ 1 , 2 , 3 , 4 , 5 , 6 , 7 ]. Both endogenous and antiviral RNA silencing initiate with the processing of double-stranded RNA by Dicer-like (DCL) proteins to form small RNAs of 21 to 24 nt that associate with Argonaute (AGO) proteins to guide slicing or translational repression of target RNAs [ 2 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. Sources of viral RNA that might trigger silencing include replication intermediates and self-complementary sequences in viral RNA, yielding primary virus-derived small interfering RNAs (siRNAs) that are necessary but not sufficient to restrict plant virus infection [ 1 ].…”

“…After initiation, antiviral RNA silencing is amplified by cellular RDR [ 3 , 9 , 10 ]. Viral silencing suppressors interfere with antiviral RNA silencing, enhancing virus accumulation at the cellular level and promoting cell-to-cell and systemic movement [ 2 , 3 , 8 , 29 , 30 ]. Accordingly, viral suppressors of RNA silencing are pathogenic factors and promote virus infection, movement, and virus accumulation in infected tissue, and regulate host range and tissue specificity [ 2 , 18 , 30 , 31 , 32 ].…”