Simulated microgravity weakens wheat root microbial network against pathogens

Fungal pathogens are well-recognized biotic stressors for plants under terrestrial gravity and also pose risks to space crop production, but their effects on root-associated microbial networks under microgravity conditions remain poorly understood. Here, we profiled bacterial and fungal communities in wheat seedlings with or without Fusarium graminearum infection under normal gravity and simulated microgravity, and linked network properties to plant growth and hormone profiles. Although bacterial and fungal α-diversity showed no significant differences among treatments and Bray-Curtis β-diversity showed limited separation, co-occurrence networks revealed that infection disrupted bacterial-bacterial and bacterial-fungal networks more strongly under simulated microgravity than under normal gravity, whereas fungal-fungal networks were largely unchanged. Bacterial network characteristics explained more variation in plant performance than bacterial-fungal network characteristics. Structural equation modeling showed that simulated microgravity reduced endosphere bacterial network stability, which was positively associated with plant performance, especially jasmonic acid and cytokinin levels. Random forest analysis identified Paenibacillus and Microbacteriaceae-related taxa as key predictors of bacterial network stability. These findings support microbiome-based strategies to enhance plant resilience in space systems.