A developmental switch controls cell-to-cell transport in roots via pectin-linked plasmodesmata changes

Cell-to-cell communication is fundamental to multicellular life. In plants, plasmodesmata - cytoplasmic channels - enable molecular transport between adjacent cells. In roots, this transport is predicted to play a central role in nutrient acquisition and delivery across the multiple cell layers that compose the root. In this study, we demonstrate that plasmodesmatal transport persists in fully differentiated roots, despite the formation of apoplastic barriers such as Casparian strips and suberin lamellae in the endodermis. This persistence highlights plasmodesmata as a critical pathway for intercellular transport in mature roots. We also uncovered a developmental switch in plasmodesmata function: while transport is bidirectional in young roots, it becomes unidirectional towards the vasculature in differentiated roots. Through a genetic screen, we identified mutants with disrupted directionality, exhibiting persistent bidirectional transport. These mutants showed enlarged plasmodesmata apertures caused by defects in pectin composition and cell wall organization, highlighting the critical role of pectin in plasmodesmata formation and function. Our findings reveal how plasmodesmata-mediated transport is dynamically regulated during root development and provide new insights into the cellular mechanisms that govern intercellular communication in plants.