Associate Member and Principal Investigator Donald Danforth Plant Science Center St. Louis, Missouri
Intercellular communication is critical for plant differentiation, growth, and defense. For many eukaryotic organisms, communication can be achieved via direct membrane contacts, but for plants, direct membrane contact between adjacent cells is precluded due to the cellulosic cell walls. As a result, plants have evolved alternative mechanisms to allow signaling and communication to neighboring cells. One of route for communication is via plasmodesmata (PD). PD are membrane-limited nano-pores that cross the cell wall to produce cytosolic and membrane continuities between adjacent cells. Molecules from metabolites to small RNAs and transcription factors move between cells via PD, eventually entering the vasculature for systemic distribution between above- and belowground systems. While PD constitute a route for communication between neighboring cells, many pathogens have evolved to manipulate PD and use them for rapid spread throughout the plant, a phenomenon best exemplified by viruses. PD that form during cytokinesis as the nascent cell wall is laid down are called primary plasmodesmata. PD may also form without cytokinesis by insertion of new PD pores into existing cell walls, a process that is common in plants, but which remains poorly understand. These latter PD are called secondary PD, and they are proposed to have trafficking functions distinct from those of primary PD. We have used advanced imaging techniques to investigate the 3D ultrastructure of PD and the distribution of these pores at various cell-cell interfaces in the presence and absence of virus infection. Leveraging the power of TEM tomography allowed us to identify possible intermediates in secondary PD formation in Nicotiana benthamiana leaves growing under normal lab conditions. We have also identified candidate proteins that have roles as positive or negative regulators of secondary PD formation. Based on these results, we propose a refined model of secondary PD formation.