The role of different innate and environmental factors in Tm-22-mediated resistance to tomato mottle mosaic virus

Tomato mottle mosaic virus (ToMMV) poses a threat to production and quality of tomato fruits. The Tm-2(2) gene confers resistance to some tobamoviruses by recognizing viral movement proteins. However, Tm-2(2)-mediated resistance against ToMMV is not well known. Here, we found that ToMMV could infect wild-type but not Tm-2(2) transgenic Nicotiana benthamiana plants and could also infect tomato cultivar Moneymaker but not resistant cultivar Jili with homozygous Tm-2(2). Chimeric viral ToMMV(ToBRFV-MP) with swapped ToMMV MP to MP of tomato brown rugose fruit virus could systemically infect Tm-2(2) transgenic N. benthamiana and tomato cultivars Jili plants. Further, transient expression of ToMMV MP in the leaves of Tm-2(2) transgenic N. benthamiana plants induced hypersensitive response-associated cell death, suggesting that the MP of ToMMV was the avirulent factor for the Tm-2(2) resistance gene. ToMMV could infect Tm-2(2)-containing cultivar Jinpeng 1 but not Chaobei. Sequence analysis revealed that cultivars Chaobei and Jinpeng 1 were heterozygous, where Chaobei consists of Tm-2(2) and Tm-2 genes, while Jinpeng 1 consists of Tm-2(2) and tm-2 genes. Transient co-expression assays showed that both Tm-2(2) and Tm-2 but not tm-2 could recognize ToMMV MP and induce hypersensitivity response-associated cell death in N. benthamiana leaves, suggesting that homozygous tomato harboring Tm-2(2) and heterozygous tomato containing Tm-2(2) and Tm-2 may exhibit more durable resistance to ToMMV than heterozygous tomato carrying Tm-2(2) and tm-2. Further, Tm-2(2) transgenic N. benthamiana and tomato cultivar Jili plants with silenced Tm-2(2) gene were susceptible to ToMMV. Also, silencing type-I J-domain MIP1 gene compromised Tm-2(2)-mediated resistance to ToMMV in Tm-2(2) transgenic N. benthamiana and tomato cultivar Jili. Moreover, we found that viral RNA could accumulate in the systemic leaves of Tm-2(2) transgenic N. benthamiana plants and tomato cultivar Jili at 35 degrees C, but not at 20, 25, or 30 degrees C. Altogether, our findings reveal that the Tm-2(2) confers resistance to ToMMV by recognizing MP, and the resistance is regulated by the allele combinations, accumulation levels of Tm-2(2), MIP1, and the temperature.