Identification of the Potential Virulence Factors and RNA Silencing Suppressors of Mulberry Mosaic Dwarf-Associated Geminivirus.

Xiuling Yang,Dongxue Wang,Dawei Li,Shifang Li,Yanxiang Ren,Xueping Zhou,Fanfan Zhang,Shaoshuang Sun

doi:10.3390/v10090472

Abstract

Plant viruses encode virulence factors or RNA silencing suppressors to reprogram plant cellular processes or to fine-tune host RNA silencing-mediated defense responses. In a previous study, Mulberry mosaic dwarf-associated virus (MMDaV), a novel, highly divergent geminivirus, has been identified from a Chinese mulberry tree showing mosaic and dwarfing symptoms, but the functions of its encoded proteins are unknown. In this study, all seven proteins encoded by MMDaV were screened for potential virulence and RNA silencing suppressor activities. We found that V2, RepA, and Rep affect the pathogenicity of a heterologous potato virus X. We showed that V2 could inhibit local RNA silencing and long-distance movement of the RNA silencing signal, but not short-range spread of the green fluorescent protein (GFP) silencing signal in Nicotiana benthamiana 16c plants. In addition, V2 localized to both subnuclear foci and the cytoplasm. Deletion mutagenesis of V2 showed that the basic motif from amino acids 61 to 76 was crucial for V2 to form subnuclear foci and for suppression of RNA silencing. Although the V2 protein encoded by begomoviruses or a curtovirus has been shown to have silencing suppressor activity, this is the first identification of an RNA silencing suppressor from a woody plant-infecting geminivirus.

Highlights

Viruses are intracellular obligate parasites that absolutely depend on the host machinery for their replication and movement
We screened for the potential virulence factors and RNA silencing suppressors encoded by Mulberry mosaic dwarf-associated virus (MMDaV)
Levels of green fluorescent protein (GFP) protein determined by Western blot analysis correlated with the visualized GFP fluorescence (Figure 3D). These results suggest that MMDaV V2 is a potent suppressor of local RNA silencing triggered by sense GFP

Summary

Introduction

Viruses are intracellular obligate parasites that absolutely depend on the host machinery for their replication and movement. RNA silencing, a fundamental sequence-specific gene regulatory process, has been demonstrated to be one of the major antiviral defense mechanisms in plants [3,6]. Viral double-stranded RNA (dsRNA) molecules of different origins, namely highly structured regions of viral single-stranded RNAs, replicative intermediates, or overlapping bidirectional read-through transcripts can trigger RNA silencing, and these are processed into 21–24 nucleotides (nt) small interfering RNAs (siRNAs) by Dicer-like RNases (DCLs). The antiviral silencing signal can be amplified by RNA-dependent RNA polymerases (RDRs). SiRNAs can act as mobile silencing signals to trigger local silencing upon movement from cell-to-cell and systemic silencing, following their transport through phloem tissues [3]

Methods

Results

Conclusion