Grafting on a Non-Transgenic Tolerant Tomato Variety Confers Resistance to the Infection of a Sw5-Breaking Strain of Tomato spotted wilt virus via RNA Silencing.

Roberta Spanò,Richard Kormelink,Donato Gallitelli,Tiziana Mascia,Neena Mitter

doi:10.1371/journal.pone.0141319

Roberta Spanò, Richard Kormelink + Show 3 more

Open Access

https://doi.org/10.1371/journal.pone.0141319

Copy DOI

Abstract

RNA silencing controls endogenous gene expression and drives defensive reactions against invasive nucleic acids like viruses. In plants, it has been demonstrated that RNA silencing can be transmitted through grafting between scions and silenced rootstocks to attenuate virus and viroid accumulation in the scions. This has been obtained mostly using transgenic plants, which may be a drawback in current agriculture. In the present study, we examined the dynamics of infection of a resistance-breaking strain of Tomato spotted wilt virus (RB-TSWV) through the graft between an old Apulian (southern Italy) tomato variety, denoted Sl-Ma, used as a rootstock and commercial tomato varieties used as scions. In tests with non-grafted plants, Sl-Ma showed resistance to the RB-TSWV infection as viral RNA accumulated at low levels and plants recovered from disease symptoms by 21 days post inoculation. The resistance trait was transmitted to the otherwise highly susceptible tomato genotypes grafted onto Sl-Ma. The results from the analysis of small RNAs hallmark genes involved in RNA silencing and virus-induced gene silencing suggest that RNA silencing is involved in the resistance showed by Sl-Ma against RB-TSWV and in scions grafted on this rootstock. The results from self-grafted susceptible tomato varieties suggest also that RNA silencing is enhanced by the graft itself. We can foresee interesting practical implications of the approach described in this paper.

Highlights

In plants, RNA silencing (RNA interference, RNAi) drives multiple regulatory and defensive reactions triggered by either endogenous or invasive double-stranded RNAs, which are diced into 21 to 24 –long ribonucleotide fragments by Dicer-like (DCL) endoribonucleases [1, 2]
The results of our study show that suitable levels of resistance against an Sw-5 resistance-breaking strain of Tomato spotted wilt virus (TSWV) (TSWV-CiPz) can be obtained in tomato by grafting the otherwise susceptible commercial varieties carrying the Sw-5 gene onto an old tomato variety, denoted S. lycopersicum cv Manduria (Sl-Ma)
The resistance trait was transmitted to susceptible tomato genotypes grafted onto Sl-Ma suggesting that a mobile signal moving through the graft junction could be implicated

Summary

Introduction

RNA silencing (RNA interference, RNAi) drives multiple regulatory and defensive reactions triggered by either endogenous or invasive double-stranded RNAs (dsRNA), which are diced into 21 to 24 –long ribonucleotide fragments by Dicer-like (DCL) endoribonucleases [1, 2]. From these fragments, generally called primary small RNAs (sRNAs), one strand becomes incorporated into members of the Argonaute (AGO) protein family to form an RNAinduced silencing complex (RISC) that starts to survey and cleave endogenous or invasive.

Methods

Results

Conclusion