The Induction of an Effective dsRNA-Mediated Resistance Against Tomato Spotted Wilt Virus by Exogenous Application of Double-Stranded RNA Largely Depends on the Selection of the Viral RNA Target Region.

Saeid Tabein,Daniele Marian,Laura Miozzi,Anna Maria Vaira,Marco Jansen,Emanuela Noris,Gian Paolo Accotto,S Ali Akbar Behjatnia

doi:10.3389/fpls.2020.533338

Abstract

Tomato spotted wilt virus (TSWV) is a devastating plant pathogen, causing huge crop losses worldwide. Unfortunately, due to its wide host range and emergence of resistance breaking strains, its management is challenging. Up to now, resistance to TSWV infection based on RNA interference (RNAi) has been achieved only in transgenic plants expressing parts of the viral genome or artificial microRNAs targeting it. Exogenous application of double-stranded RNAs (dsRNAs) for inducing virus resistance in plants, namely RNAi-based vaccination, represents an attractive and promising alternative, already shown to be effective against different positive-sense RNA viruses and viroids. In the present study, the protection efficacy of exogenous application of dsRNAs targeting the nucleocapsid (N) or the movement protein (NSm) coding genes of the negative-sense RNA virus TSWV was evaluated in Nicotiana benthamiana as model plant and in tomato as economically important crop. Most of the plants treated with N-targeting dsRNAs, but not with NSm-targeting dsRNAs, remained asymptomatic until 40 (N. benthamiana) and 63 (tomato) dpi, while the remaining ones showed a significant delay in systemic symptoms appearance. The different efficacy of N- and NSm-targeting dsRNAs in protecting plants is discussed in the light of their processing, mobility and biological role. These results indicate that the RNAi-based vaccination is effective also against negative-sense RNA viruses but emphasize that the choice of the target viral sequence in designing RNAi-based vaccines is crucial for its success.

Highlights

Tomato spotted wilt virus (TSWV), genus Orthotospovirus, family Tospoviridae, belongs to the list of the ten most economically important viruses in the world (Scholthof et al, 2011) and is able to cause high yield losses in a variety of crops and ornamentals, in tropical and subtropical regions (Pappu et al, 2009; Mitter et al, 2013; Turina et al, 2016)
In order to select the genomic regions of TSWV most suitable as target by double-stranded RNAs (dsRNAs), we first considered the viral small RNAs (vsRNAs) profile of TSWV available in the literature (Mitter et al, 2013; Margaria et al, 2015), starting from the hypothesis that the genomic regions characterized by a high number of mapping vsRNAs could be more subjected to RNA interference (RNAi)-mediated degradation
According to Mitter et al (2013), most vsRNAs detected in TSWV-infected N. benthamiana plants mapped to the M segment, followed by the S segment, while the L RNA had the least number of mapping vsRNAs

Summary

Introduction

Tomato spotted wilt virus (TSWV), genus Orthotospovirus, family Tospoviridae, belongs to the list of the ten most economically important viruses in the world (Scholthof et al, 2011) and is able to cause high yield losses in a variety of crops and ornamentals, in tropical and subtropical regions (Pappu et al, 2009; Mitter et al, 2013; Turina et al, 2016) It has a wide host range and is transmitted by thrips in a persistent manner (Whitfield and Rotenberg, 2015). Few resistance genes against TSWV have been identified and introgressed in commercial cultivars (Turina et al, 2016); the frequent appearance of resistance-breaking isolates, together with the difficulty of selecting and incorporating new resistance genes stress the needs of developing new strategies for protecting plants against TSWV infection

Methods

Results

Conclusion