Fine mapping and identification of two NtTOM2A homeologs responsible for tobacco mosaic virus replication in tobacco ( Nicotiana tabacum L.)

Background Tobacco mosaic virus (TMV) is a widely distributed viral disease that threatens many vegetables and horticultural species. Using the resistance gene N which induces a hypersensitivity reaction, is a common strategy for controlling this disease in tobacco ( Nicotiana tabacum L . ). However, N gene-mediated resistance has its limitations, consequently, identifying resistance genes from resistant germplasms and developing resistant cultivars is an ideal strategy for controlling the damage caused by TMV. Results Here, we identified highly TMV-resistant tobacco germplasm, JT88, with markedly reduced viral accumulation following TMV infection. We mapped and cloned two tobamovirus multiplication protein 2A ( TOM2A ) homeologs responsible for TMV replication using an F 2 population derived from a cross between the TMV-susceptible cultivar K326 and the TMV-resistant cultivar JT88. Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (CRISPR/Cas9)-mediated loss-of-function mutations of two NtTOM2A homeologs almost completely suppressed TMV replication; however, the single gene mutants showed symptoms similar to those of the wild type. Moreover, NtTOM2A natural mutations were rarely detected in 577 tobacco germplasms, and CRISPR/Cas9-mediated variation of NtTOM2A led to shortened plant height, these results indicating that the natural variations in NtTOM2A were rarely applied in tobacco breeding and the NtTOM2A maybe has an impact on growth and development. Conclusions The two NtTOM2A homeologs are functionally redundant and negatively regulate TMV resistance. These results deepen our understanding of the molecular mechanisms underlying TMV resistance in tobacco and provide important information for the potential application of NtTOM2A in TMV resistance breeding.