N gene enhances resistance to Chilli veinal mottle virus and hypersensitivity to salt stress in tobacco

Plants use multiple mechanisms to fight against pathogen infection. One of the major mechanisms involves the disease resistance (R) gene, which specifically mediates plant defense. Recent studies have shown that R genes have broad spectrum effects in response to various stresses. N gene is the resistance gene specifically resistant to Tobacco mosaic virus (TMV). However, the role of N gene in abiotic stress and other viral responses remains obscure. In this study, we investigated the mechanisms by which N regulates plant defense responses under Chilli veinal mottle virus (ChiVMV) infection and salt stress. Here, we monitored the physiological and molecular changes of tobacco plants under virus attack. The results showed that when tobacco^NN and tobaccoⁿⁿ plants were exposed to ChiVMV, tobacco^NN plants displayed higher susceptibility at five days post infection (dpi), while tobaccoⁿⁿ plants exhibited higher susceptibility at 20 dpi. In addition, accumulation of reactive oxygen species (ROS) and expression of HARPIN-INDUCED1(NtHIN1) were higher in tobacco^NN plants than in tobaccoⁿⁿ plants at 5 dpi. Interestingly, the pathogenesis-related gene (NtPR1 and NtPR5), the activities of antioxidant enzymes, and the content of salicylic acid (SA) in tobacco^NN plants increased compared with those in tobaccoⁿⁿ plants. It was suggested that the N gene induced a hypersensitive response (HR) and enhanced the systemic resistance of plants in response to ChiVMV via the SA-dependent signaling pathway. In addition, the N gene was also induced significantly by salt stress. However, tobacco^NN plants showed hypersensitivity toward increased salt stress, and this hypersensitivity was dependent on abscisic acid and jasmonic acid but not SA. Taken together, our results indicate that the N gene appears to be important in the plant response to ChiVMV infection and salt stress.