Transport of proteins and nucleic acids through plasmodesmata

Despite a potentially key role in cell-to-cell communication, plant intercellular connections - the plasmodesmata - have long been a biological "black box." Little is known about their protein composition, regulatory mechanisms, or transport pathways. However, recent studies have shed some light on plasmodesmal function. These connections have been shown to actively traffic proteins and protein-nucleic acid complexes between plant cells. This review describes these transport processes - specifically, cell-to-cell movement of plant viruses as well as endogenous cellular proteins - and discusses their possible mechanism(s). For comparison and to provide a broader perspective on the plasmodesmal transport process, the current model for nuclear import, the only other known example of transport of large proteins and protein-nucleic acid complexes through a membrane pore, is summarized. Finally, the function of plasmodesmata as communication boundaries within plant tissue is discussed.