Identification of genes involved in the tomato Mi-1-mediated immunity to root-knot nematodes parasitism under high temperature

Root-knot nematodes (RKNs) are notorious plant pathogens that cause substantial losses in horticultural crops globally. The tomato RKN resistance gene, Mi-1, is currently the sole commercially available source of resistance. However, its effectiveness significantly declines when soil temperatures exceed 28 °C. Although numerous studies have explored the immune signaling pathways mediated by Mi-1, the specific plant immune responses affected by high temperatures and the key temperature-sensitive genes involved remain poorly understood. In this study, we demonstrated that the Mi-1-mediated hypersensitive response is impaired at 32 °C. At this temperature, the production of reactive oxygen species (ROS) in roots is reduced, while callose deposition increases. Through comparative transcriptome analysis between 24 °C and 32 °C, we identified significant changes in hormone signaling pathways, immune signaling, and gene alternative splicing. For instance, the jasmonate (JA) pathway was upregulated, and the salicylic acid (SA) pathway was inhibited at 32 °C. High temperatures also disrupted the MAPK cascade and influenced metabolite synthesis. Notably, most genes upregulated at 24 °C were downregulated at 32 °C. Furthermore, virus-induced gene silencing (VIGS) assays verified that interfering with the expression of differentially expressed genes, such as the JA biosynthesis key gene MYB transcription factor AOS3, the abscisic acid (ABA) synthesis regulation gene JA2, and the heat stress transcription factor A-6b, increased the susceptibility of Mi-1 tomatoes to RKNs. These findings offer crucial insights into the temperature sensitivity of Mi-1 resistance and support the development of RKN-resistant tomatoes that can remain effective under high-temperature conditions.