Understanding how plants adapt to the unique pressures of spaceflight is critical for growing food in deep space. Microbial plant pathogens were recently isolated from the International Space Station (ISS), and disease loss threatens crop production in space. To sustain long duration human space exploration, we need to grow and harvest edible crops and minimize crop loss from disease. This requires knowledge of plant immune responses during spaceflight, and how pathogen colonization and virulence are impacted by spaceflight conditions. However, our current knowledge of plant-microbe interactions in space is very limited. The Advanced Plant Habitat (APH) is a recently developed plant growth system that provides improved growing conditions during spaceflight. We are investigating how the tomato immune system adapts to spaceflight when grown in the APH aboard the ISS. We will grow both wild type and immune-deficient tomatoes in the APH and elicit defense responses with a chemical elicitor. Upon return to Earth, genome-wide transcriptional profiling will compare the immune responses of space-grown tomatoes to ground controls. We are also investigating how tomato colonization by a fungal pathogen, Fusarium oxysporum, is altered by simulated microgravity on Earth. Our results will reveal fundamental insights into how the plant immune system responds to spaceflight conditions. Results will contribute to the development of sustainable crop production strategies in space and will enhance NASA’s human exploration activities.