Journal
MOLECULAR PLANT PATHOLOGY
Volume 23, Issue 5, Pages 622-633Publisher
WILEY
DOI: 10.1111/mpp.13182
Keywords
alanine scan mutagenesis; resistance breaking; resistance gene; Sw-5b; tomato spotted wilt virus
Categories
Funding
- Natural Science Foundation of Jiangsu Province [BK20180532]
- National Natural Science Foundation of China [31630062, 31925032, 31870143, 31801705]
- Youth Science and Technology Innovation Program
- Fundamental Research Funds for the Central Universities [JCQY202104]
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Sw-5b is an effective resistance gene in tomato against TSWV, but mutations in the viral protein NSm can lead to resistance-breaking isolates. By mutagenizing specific amino acids in NSm21, key residues for Sw-5b recognition were determined, and improved mutants were engineered to provide effective resistance against field and potential RB TSWV isolates.
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-5b(L33P/K319E/R927A) and Sw-5b(L33P/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.
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