Extracellular Vesicles of a Phytobeneficial Bacterium Trigger Distinct Systemic Response in Plant

Bacterial extracellular vesicles (EVs) are lipidic shuttles involved in inter-species communication, virulence, and host immune modulation. While their roles are increasingly understood in animal-bacteria interactions, knowledge of phytobacterial EVs remains limited. Recent findings indicate that biotic factors like hydroxycinnamic acids can regulate EV production. Hydroxycinnamic acids, such as ferulic acid, are abundant lignin components in the plant environment, influencing the ecology of numerous phytobacteria. Azospirillum sp. B510, a phytobeneficial bacterium, induces the accumulation of hydroxycinnamic acid derivatives in plants and can metabolise them. This study hypothesised that ferulic acid in the Azospirillum sp. B510 environment would influence EV production and, conversely, that these EVs would impact plant metabolites and defence gene expression. Our results demonstrate that ferulic acid influences the content of EVs released by Azospirillum sp. B510. Furthermore, bacterial EVs impact plant physiology at a systemic level according to their cargo. EVs induce systemic changes in Solanum lycopersicum metabolome, including alterations in hydroxycinnamic acid amide derivatives in roots and steroidal alkaloids in aerial tissues. Bacterial EVs also modulate tomato defence gene expression correlating with observed metabolite accumulation patterns. This research provides evidence of a global effect of bacterial EVs, highlighting the dynamic nature of plant-bacteria interactions mediated by EVs.