Determination of key residues in tospoviral NSm required for Sw‐5b recognition, their potential ability to overcome resistance, and the effective resistance provided by improved Sw‐5b mutants

Abstract

Sw‐5b is an effective resistance gene used widely in tomato to control tomato spotted wilt virus (TSWV), which causes severe losses in crops worldwide. Sw‐5b confers resistance by recognizing a 21‐amino‐acid peptide region of the viral movement protein NSm (NSm21, amino acids 115–135). However, C118Y or T120N mutation within this peptide region of NSm has given rise to field resistance‐breaking (RB) TSWV isolates. To investigate the potential ability of TSWV to break Sw‐5b‐mediated resistance, we mutagenized each amino acid on NSm21 and determined which amino acid mutations would evade Sw‐5b recognition. Among all alanine‐scan mutants, NSmP119A, NSmW121A, NSmD122A, NSmR124A, and NSmQ126A failed to induce a hypersensitive response (HR) when coexpressed with Sw‐5b in Nicotiana benthamiana leaves. TSWV with the NSmP119A, NSmW121A, or NSmQ126A mutation was defective in viral cell‐to‐cell movement and systemic infection, while TSWV carrying the NSmD122A or NSmR124A mutation was not only able to infect wild‐type N. benthamiana plants systemically but also able to break Sw‐5b‐mediated resistance and establish systemic infection on Sw‐5b‐transgenic N. benthamiana plants. Two improved mutants, Sw‐5bL33P/K319E/R927A and Sw‐5bL33P/K319E/R927Q, which we recently engineered and which provide effective resistance against field RB isolates carrying NSmC118Y or NSmT120N mutations, recognized all NSm21 alanine‐substitution mutants and conferred effective resistance against new experimental RB TSWV with the NSmD122A or NSmR124A mutation. Collectively, we determined the key residues of NSm for Sw‐5b recognition, investigated their potential RB ability, and demonstrated that the improved Sw‐5b mutants could provide effective resistance to both field and potential RB TSWV isolates.

Deciphering the Role of Virus Receptors in Plant–Virus–Vector Interactions

“…TSWV strains overcoming resistance against Sw-5b in tomato was reported from various regions at different time points [95,96]. The resistance-breaking phenotype was associated with amino acid substitutions in NSm, namely C118Y, T120N, and D122G [97][98][99]. Similarly, in pepper, TSWV-resistant breaking strains were reported from different regions [100,101].…”

Tomato brown rugose fruit virus: An emerging and rapidly spreading plant RNA virus that threatens tomato production worldwide

“…In cases where the R ‐mediated resistance has been overcome, random mutagenesis as well as stepwise artificial evolution may be employed to generate R mutants to restore resistance (Tamborski & Krasileva, 2020 ). For instance, Sw‐5b confers strong resistance to TSWV and new isolates with two single mutations C118Y or T120N in the NSm protein can overcome Sw‐5b ‐mediated immunity (Huang et al, 2022 ). Using a stepwise artificial evolution strategy, Huang and colleagues successfully generated two Sw‐5b mutants that confer resistance to TSWV in transgenic plants (Huang et al, 2021 ).…”

Identification of a new type of resistance breaking strain of tomato spotted wilt virus on tomato bearing the Sw-5b resistance gene

“…In the case of different TSWV RB strains on pepper, no common amino acid (aa) alteration can be observed in the NSs Avr protein, but in the case of the Sw-5b gene in tomato, two distinct aa alterations were identified in all the RB TSWV strains. The RB phenotype was linked to one of the two single specific aa substitutions in the Avr determinant NSm, namely C118Y or T120N (Huang et al, 2022;Lopez et al, 2011).…”