Non-Structural Protein NSm of Tomato Spotted Wilt Virus Is an Avirulence Factor Recognized by Resistance Genes of Tobacco and Tomato via Different Elicitor Active Sites

Abstract

Tomato spotted wilt virus (TSWV) is one of the most destructive viral pathogens of plants. Recently, a single dominant gene conferring complete resistance to TSWV (RTSW) was identified in Nicotina alata and introgressed into cultivated tobacco (N. tabacum). However, whether the TSWV carries an avirulence (Avr) factor directed against RTSW remains obscure. In the present study, we identified the non-structural protein (NSm), the movement protein of TSWV, which is an RTSW-specific Avr factor, by using two different transient expression systems. Using amino acid (aa) substitution mutants, we demonstrated the ability to induce RTSW-mediated hypersensitive response (HR) of NSm is independent of its movement function. Moreover, key substitutions (C118Y and T120N), a 21-aa viral effector epitope, and different truncated versions of NSm, which are responsible for the recognition of the Sw-5b resistance gene of tomato, were tested for their ability to trigger HR to TSWV in tobacco. Together, our results demonstrated that RTSW-mediated resistance is triggered by NSm in the same way as by Sw-5b, however, via different elicitor active sites. Finally, an Avr gene-based diagnostic approach was established and used to determine the presence and effectiveness of resistance genes in tobacco.

Tracing the Lineage of Two Traits Associated with the Coat Protein of the Tombusviridae: Silencing Suppression and HR Elicitation in Nicotiana Species

“…Agroinfiltration is a powerful tool for the discovery and initial characterization of pathogen proteins capable of triggering HR in plant hosts. This tool has been validated for several virus avr proteins including the cauliflower mosaic virus P6 protein [45] and the helicase domain of the tobacco mosaic virus (TMV) replicase [46,47], the NSm gene of tomato spotted wilt virus (TSWV) [48] as well as the P19 and P22 proteins of TBSV [40]. For each of these virus avr genes, the avr trait was first identified through techniques involving either gene swaps between virus strains [49,50], the insertion of the avr gene into a virus vector [51,52], or direct mutagenesis of the avr gene within an infectious clone of the virus [53].…”

From Player to Pawn: Viral Avirulence Factors Involved in Plant Immunity

“…RTSW , another R locus from wild tobacco N. alata that confers ER to TSWV, has been introgressed into cultivated tobacco. By using two different transient expression systems, we showed that the NSm protein of TSWV acts as an Avr determinant of RTSW -based resistance [ 61 ]. Moreover, both our results and those of Tao’s group showed that intercellular trafficking of NSm can be uncoupled from its HR function in the induction of RTSW and Sw-5b resistance [ 61 , 102 ].…”

“…By using two different transient expression systems, we showed that the NSm protein of TSWV acts as an Avr determinant of RTSW -based resistance [ 61 ]. Moreover, both our results and those of Tao’s group showed that intercellular trafficking of NSm can be uncoupled from its HR function in the induction of RTSW and Sw-5b resistance [ 61 , 102 ]. More importantly, our evidence indicates that although RTSW and Sw-5b behave as single dominant genes that confer ER by interacting with the same NSm protein encoded by the same virus, they recognize different elicitor domains (EADs) [ 61 ].…”

Host Plant Strategies to Combat Against Viruses Effector Proteins

“…Approximately 500 species of plant pathogenic viruses that are responsible for various diseases are considered an intracellular parasite [ 76 ]. Because viruses encode relatively few proteins, such as coat proteins, replication proteins, P25 protein, RNA-dependent RNA polymerase, helicase, P3 protein, HcPro proteins, NIa protease, NSs protein, viral protein genome-linked, and virus movement proteins, all are known to assist as Avr factors in different plant/viral systems [ 77 ]. The basic noticeable feature of gene-for-gene mediated resistance is the development of an HR by the plant against phytopathogens [ 78 ] wherein necrotic lesions or ringspots are developed at the location of infection on leaves, stems, and fruits, confining the phytopathogen within it and thus protecting noninfected tissues (Fig.…”