Plasmodesmata: A new frontier for membrane contact site intercellular communication

Membrane contact sites (MCSs) serve a critical role in intracellular communication, particularly between organelle membranes, enabling direct molecular transfer. Less clear is the role MCSs play in intercellular communication. New evidence from Pérez-Sancho et al. implicates plasmodesmata in this function and their endoplasmic reticulum-plasma membrane (ER-PM) MCSs. Unique to land plants and some green algae is an ER network that spans between cells (which is closely associated with the PM to form plasmodesmata). Historically, callose synthesis/degradation was the only established process for understanding plasmodesmata trafficking flow. The authors hypothesized that the MCS within plasmodesmata might act as a control valve for intercellular communication. They first identified core ER-PM tethering proteins (MCTP3, MCTP4, and MCTP6), then observed greater plasmodesmata diameter in Arabidopsis thaliana mutants for these proteins. Further, the mutants had faster molecular flow and reduced dynamic control when exposed to stressors compared to wild type, all independent of callose deposition mechanisms. The authors also characterized an anionic phospholipid (PI4P) that regulates MCTP4 docking to the PM, collectively working to fluctuate plasmodesmata permeability highly dependent on their own molecular regulators (including SAC7), which were shown to be differentially expressed in root cell types. Taken together, Pérez-Sancho et al. have highlighted an intricate regulatory network between cells via plasmodesmata. Their work finds a new intercellular function for MCSs with a control mechanism beyond just callose deposition. (Summary by Stephanie Temnyk @STemnyk) Cell 10.1016/j.cell.2024.11.034