Extracellular vesicles of a phytobeneficial bacterium trigger distinct systemic response in plant

Bacterial extracellular vesicles (EVs) are lipidic shuttles that play roles in virulence, inter-species competition, and in the induction of the host immune response. While they have primarily been investigated in animal-bacteria interactions, knowledge regarding phytobacterial EVs remains limited. Recent findings revealed that various biotic factors like hydroxycinnamic acids can regulate EVs production. Hydroxycinnamic acids, such as ferulic acid, are lignin components abundantly released in the plant environment, where they impact the ecology of numerous phytobacteria. Azospirillum sp. B510, a phytobeneficial bacterium, induces the accumulation of hydroxycinnamic acid derivatives in the plant and can metabolize them as carbon sources. We hypothesized that the presence of ferulic acid in the environment of Azospirillum sp. B510 would influence its EVs production in terms of size, quantity, and cargo. Conversely, we also proposed that EVs from this phytobacterium would influence plant metabolites and defense gene expression. Our results show both that ferulic acid (mimicking the plant environment) influences the content of EVs released by Azospirillum sp. B510 and that bacterial EVs also impact plant physiology at a systemic level according to their cargoes. This research provides the first evidence of a global effect of bacterial EVs on the plant and highlights the dynamics of plant-bacteria interactions mediated by EVs.