Infection Reinforces the Defense Reactions in - Roots to the Detriment of Nodules.

, able to establish symbiosis with mutualistic bacteria of the genus , is one of the main species in European riparian environments, where it performs numerous biological and socio-economic functions. However, riparian ecosystems face a growing threat from , a highly aggressive waterborne pathogen causing severe dieback in . To date, the tripartite interaction between the host plant, the symbiont and the pathogen remains unexplored but is critical for understanding how pathogen-induced stress influences the nodule molecular machinery and so on the host-symbiont metabolism. In the present study, we aimed to explore for the first time how affects the overall molecular processes of - nodules, with a special focus on unraveling the spatial expression of defense mechanisms within these tissues. We conducted a laboratory experiment based on infection of young seedlings nodulated with ACN14a, non-infected or infected with the pathogen . Multi-omics analyses were carried out on nodules (N) and associated roots (AR) of the same plant in order to underline the impact on the nodule molecular processes (i.e. N/AR markers) when the host plant is infected compared to non-infected plants. Our results revealed that infection modified the molecular nodule processes and induced reprograming of defense-related markers by a shift in associated roots to the detriment of nodules. These findings suggest that reinforces locally its immune responses in roots but moderates this activation in nodule to preserve its symbiont.