Small RNA mobility and plant virus diseases.

Plants rely on symplasmic networks of cell-to-cell and long-distance communication through plasmodesmata and phloem to regulate plant development and adaptations to environmental changes. Plasmodesmata facilitate the intercellular transport of metabolites, phytohormones, proteins and RNA molecules, many of which act as signaling molecules. Among these, non-cell-autonomous RNA molecules play a crucial role in coordinating plant development, gene silencing, stress responses, nutrient allocation, as well as in antiviral defense and host-parasite interactions. This review explores the mechanisms of cell-to-cell and systemic mobility of small RNAs, with a particular emphasis on the role of virus- and host-derived small RNAs in regulating the outcome of viral infection in terms of disease, resistance and tolerance.