Rhizosecreted exosome-like nanoparticles mediate plant communication in rice (Oryza sativa L.) under salinity stress

ABSTRACT Rhizosecretion of extracellular vesicles or exosome-like nanoparticles (ELNs) is a continuous process, and the cargo represents the physiological status of the donor plant. Plant communication is a vital survival mechanism, yet the role of ELNs in mediating belowground signalling remains poorly understood. This study investigates whether rice ( Oryza sativa L.) seedlings utilize rhizosecreted ELNs to transmit salinity stress signals to neighbouring plants. ELNs were isolated from hydroponic media using differential ultracentrifugation and characterized via DLS, SEM, and TEM, revealing spherical vesicles with mean diameters between 30 and 150 nm. Using FM 4-64 labelling and confocal microscopy, we demonstrated that rice roots uptake these ELNs through rhizo-absorption. The unstressed "receiver" seedlings treated with an ELN-enriched fraction derived from salt-stressed (200 mM NaCl) donor plants exhibited significant differential expression of key antioxidant genes. Conversely, treatment with ELN-depleted media failed to induce these molecular responses. Furthermore, co-incubation experiments with salt-tolerant (Pokkali) and salt-sensitive (Uma) rice varieties demonstrated that below-ground communication alone is sufficient to trigger stress response in neighbouring plants. These findings suggest that rhizosecreted ELNs and their cargo function as distant mobile signals and induce transcript- and biochemical- level responses in the receiver plants.