Isolation and characterisation of watermelon (Citrullus lanatus) extracellular vesicles and their cargo

Extracellular vesicles (EVs) facilitate cell-cell communication in animals and are integral to many physiological and pathological processes. Evidence for the presence and function of EVs in plants is limited. Here, we report that EVs derived from watermelon fruit mesocarp are of similar size and morphology to the animal EV subtype known as exosomes. Analysis of EV constituents revealed that watermelon EVs are negative for endoplasmic reticulum markers, and that the miRNA and protein profiles differ from that of watermelon mesocarp cells, suggesting that these EVs are actively synthesised and are not merely cellular debris. Furthermore, we report a panel of proteins found in in watermelon EVs as well as the published proteomes of grape, grapefruit, lemon and Arabidopsis thaliana EVs that are novel potential plant EV markers. Bioinformatic analyses suggest that plastids and multivesicular bodies are likely sites of biogenesis for EVs from watermelon and other plants. Predicted functional roles of watermelon EVs include development and metabolism, with several of their cargo molecules likely to be key in regulation of fruit development and ripening. Further understanding of how EVs may contribute to these processes would improve understanding of plant cell-cell communication and could aid in the harnessing of plant EVs for greater temporal control of crop development/ripening for the agricultural and retail industries.