Primers used in this study.

Tomato brown rugose fruit virus (ToBRFV) is a rapidly spreading pathogen that poses a significant threat to tomato production worldwide. We previously identified a locus on tomato chromosome 11 controlling tolerance to the virus. We further established that combining this locus with one that maps to the Tm-1 region on chromosome 2 confers resistance to the virus. Here we sought to determine whether, and how, the Tm-1 gene itself is involved in ToBRFV resistance. Overexpression of Tm-1 in a tolerant genotype significantly reduced viral accumulation, conferring resistance to ToBRFV. On the other hand, overexpression of Tm-1 in a susceptible genotype only delayed symptom appearance. Moreover, effective RNAi-silencing of Tm-1 in the resistant genotype yielded susceptible plants. These findings show that the Tm-1 gene interacts genetically with the locus controlling tolerance on chromosome 11 and that this interaction is critical for achieving effective resistance to ToBRFV. In addition, the symptomatic plants obtained following silencing of Tm-1 in the resistant genotype indicate that tolerance is also dependent on normal expression levels of the recessive tm-1 allele.