Tsw gene‐based resistance is triggered by a functional RNA silencing suppressor protein of the Tomato spotted wilt virus

Abstract

As a result of contradictory reports, the avirulence (Avr) determinant that triggers Tsw gene-based resistance in Capsicum annuum against the Tomato spotted wilt virus (TSWV) is still unresolved. Here, the N and NSs genes of resistance-inducing (RI) and resistance-breaking (RB) isolates were cloned and transiently expressed in resistant Capsicum plants to determine the identity of the Avr protein. It was shown that the NSs(RI) protein triggered a hypersensitive response (HR) in Tsw-containing Capsicum plants, but not in susceptible Capsicum, whereas no HR was discerned after expression of the N(RI) (/) (RB) protein, or when NSs(RB) was expressed. Although NSs(RI) was able to suppress the silencing of a functional green fluorescence protein (GFP) construct during Agrobacterium tumefaciens transient assays on Nicotiana benthamiana, NSs(RB) had lost this capacity. The observation that RB isolates suppressed local GFP silencing during an infection indicated a recovery of RNA silencing suppressor activity for the NSs protein or the presence of another RNA interference (RNAi) suppressor. The role of NSs as RNA silencing suppressor and Avr determinant is discussed in the light of a putative interplay between RNAi and the natural Tsw resistance gene.

The NSs Protein of Tomato spotted wilt virus Is Required for Persistent Infection and Transmission by Frankliniella occidentalis

“…No mutant defective in functional NSs accumulation was described in more than 30 years of tospovirus molecular studies. We and, more recently, other authors have demonstrated that mutations in a functional NSs protein are responsible for overcoming the resistance provided by the Tsw gene in pepper (21,26). Among the RB isolates we described, a subset was characterized by deletions in the NSs coding region that caused a frameshift and expression of truncated proteins.…”

Phylogenetic analysis of Tomato spotted wilt virus (TSWV) NSs protein demonstrates the isolated emergence of resistance-breaking strains in pepper

“…The rapid adaptation of TSWV to pepper resistance and breakdown of the Tsw resistance gene facilitated the determination of the avr factor (avr) of TSWV, and the study of the evolutionary aspects of emergence of new strains [15,[20][21][22][23][24][25][26][27]. However, contradictory results, lacking information and methodological difficulties hinder or delay advances in these questions.…”

“…De Ronde et al [15] succeeded to prove directly the independent role of NSs protein both in Tsw gene-mediated resistance and in RNA silencing suppression by transient expression [16]. For this reason, we chose S RNA segment of the Hungarian TSWV pepper strains to determine differences between the RB and WT isolates in nucleotide and (deduced) aa sequences.…”

“…From the S RNA, two proteins are translated: the nucleocapsid (N) and a nonstructural protein (NSs) [14]. According to de Ronde et al [15], NSs is the suppressor protein of the host plant gene silencing mechanism and it is responsible for breakdown of the plant's resistance (avirulence factor, avr). The contribution of the different domains of the protein to the gene silencing function and as avr factor was recently analyzed in detail [16].…”

A Violaxanthin Deepoxidase Interacts with a Viral Suppressor of RNA Silencing to Inhibit Virus Amplification

“…In many cases, R proteins interact with VSRs that also act as Avr factors, leading to the activation of defense responses (Cooley et al, 2000;de Ronde et al, 2013;Wen et al, 2013;Boualem et al, 2016). Intriguingly, some host factors involved in counter-counter defense against VSRs have been identified.…”