The cytosol must flow: intercellular transport through plasmodesmata

• PD are nanoscopic channels connecting plant cells across cell walls.
• Transcription factors, RNAs, and hormones move through PD to control development.
• Restricting PD transport is critical for cell differentiation and plant development.
• Chloroplasts and mitochondria regulate PD transport and cell–cell signaling.
• PD convergently evolved in plants and several algal lineages.

Plant cells are connected across cell walls by nanoscopic channels called plasmodesmata (PD), which allow plant cells to share resources and exchange signaling molecules. Several protein components of PD membranes have been identified, and recent advances in superresolution live-cell microscopy are illuminating PD ultrastructure. Restricting transport through PD is crucial for morphogenesis, since hormones and hundreds of transcription factors regularly move through PD, and this transport must stop to allow cells to begin differentiating. Chloroplasts and mitochondria regulate PD function through signal transduction networks that coordinate plant physiology and development. Recent discoveries on the relationships of land plants and their algal relatives suggest that PD have evolved independently in several lineages, emphasizing the importance of cytosolic bridges in multicellular biology.

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