Synergistic infection of BrYV and PEMV 2 increases the accumulations of both BrYV and BrYV-derived siRNAs in Nicotiana benthamiana

Cui-Ji Zhou,Da-Wei Li,Xiao-Yan Zhang,Song-Yu Liu,Cheng-Gui Han,Jia-Lin Yu,Ying Wang

doi:10.1038/srep45132

Abstract

Viral synergism is caused by co-infection of two unrelated viruses, leading to more severe symptoms or increased titres of one or both viruses. Synergistic infection of phloem-restricted poleroviruses and umbraviruses has destructive effects on crop plants. The mechanism underlying this synergy remains elusive. In our study, synergism was observed in co-infections of a polerovirus Brassica yellows virus (BrYV) and an umbravirus Pea enation mosaic virus 2 (PEMV 2) on Nicotiana benthamiana, which led to (1) increased titres of BrYV, (2) appearance of severe symptoms, (3) gain of mechanical transmission capacity of BrYV, (4) broader distribution of BrYV to non-vascular tissues. Besides, profiles of virus-derived small interfering RNAs (vsiRNAs) from BrYV and PEMV 2 in singly and doubly infected plants were obtained by small RNA deep sequencing. Our results showed that accumulation of BrYV vsiRNAs increased tremendously and ratio of positive to negative strand BrYV vsiRNAs differed between singly infected and co-infected plants. Positions to which the BrYV vsiRNAs mapped to the viral genome varied considerably during synergistic infection. Moreover, target genes of vsiRNAs were predicted and annotated. Our results revealed the synergistic characteristics during co-infection of BrYV and PEMV 2, and implied possible effects of synergism have on vsiRNAs.

Highlights

RNA silencing, a highly conserved mechanism in various eukaryotic organisms, regulates gene expression and plays a major role in antiviral immunity[1,2]
It has been reported that synergistic interaction between crinivirus Sweet potato chlorotic stunt virus (SPCSV) and begomovirus Sweet potato leaf curl virus isolate StV1 in sweet potato leads to specific changes in the relative abundance and distribution of SPCSV-derived siRNAs, implying a distinctive influence of begomoviruses on RNA silencing of SPCSV in synergy[29]
To examine whether synergism occurs between Brassica yellows virus (BrYV) and Pea enation mosaic virus 2 (PEMV 2), N. benthamiana plants at 3–4 leaf stage were agroinfiltrated with empty vector (Mock), BrYV, PEMV 2 and BrYV + PEMV 2, respectively

Summary

Introduction

RNA silencing, a highly conserved mechanism in various eukaryotic organisms, regulates gene expression and plays a major role in antiviral immunity[1,2]. A typical trait of antiviral silencing in plants is production of virus-derived small interfering RNAs (vsiRNAs)[3,4,5]. For positive-strand plant RNA viruses, vsiRNAs are processed either from highly structured regions of viral genome or double-stranded viral RNA replication intermediates by Dicer-like (DCL) proteins[6,7]. These vsiRNAs are recruited by ARGONAUTE (AGO) containing RNA induced silencing complex (RISC) to guide them to the complementary viral RNAs or host transcripts in a sequence-specific manner[2,8,9,10]. It has been reported that synergistic interaction between crinivirus Sweet potato chlorotic stunt virus (SPCSV) and begomovirus Sweet potato leaf curl virus isolate StV1 in sweet potato leads to specific changes in the relative abundance and distribution of SPCSV-derived siRNAs, implying a distinctive influence of begomoviruses on RNA silencing of SPCSV in synergy[29]

Methods

Results

Conclusion