Outer Membrane Vesicles (OMVs) Produced by Plant Beneficial Rhizospheric Bacteria Enter Root Epidermal Cells

Extracellular vesicles (EVs) are shown to play an important role in the interaction between bacteria and human cells, as well as between fungi and plants; however, much less is known about their role in plant-bacteria relations. Outer membrane vesicles (OMVs), EVs produced by Gram-negative bacteria, were shown to have both immuno-activating and immuno-suppressive effects on plants, and a direct interaction of OMVs with plant cell membranes was shown for one phytopathogenic bacterial strain. Data on OMVs participation in the symbiotic relationship between plant-beneficial bacteria and plants are even more limited, and are mainly related to the rhizobia-legume interaction. To investigate the interaction of OMVs of non-rhizobial phytobeneficial bacteria with plant cells, we isolated and characterized OMVs produced by Paraburkholderia phytofirmans PsJN, a strain well known for its growth-promoting and stress-protective effects in a wide range of plant species. Using OMVs labelled with fluorescent lipid-binding dye VybrantTM DiD and confocal laser scanning microscopy, we showed that PsJN-OMVs interact directly with the root hairs and epidermal cells of Arabidopsis thaliana and tomato. Moreover, by employing octadecyl-rhodamine B chloride (R18), we demonstrated that PsJN-OMVs can fuse with plant cell membranes. The findings presented in our study are an important step in elucidating the potential role of OMVs in the early stages of root colonization and the establishment of symbiotic relationships. Increasing our understanding in this area could pave the way for the use of these nano-vehicles to develop eco-friendly solutions for overcoming environmental challenges and supporting sustainable agriculture.