Gene expression profiling by RNA-seq in the roots of wild-type, mctp4-1 single mutant (M6), mctp3-2 single mutant (M8) and mctp3-2/mctp4-1 double mutant (C2) Arabidopsis thaliana seedlings.
Membrane contact sites (MCS) are fundamental for intracellular communication, but their role in intercellular communication remains unexplored. We show that in plants, plasmodesmata communication bridges function as atypical endoplasmic reticulum (ER)-plasma membrane (PM) tubular MCS, operating at cell-cell interfaces. Similar to other MCS, ER-PM apposition is controlled by a protein-lipid tethering complex, but uniquely, this serves intercellular communication. Combining high-resolution microscopy, molecular dynamics, pharmacological and genetic approaches, we show that cell-cell trafficking is modulated through the combined action of Multiple C2 domains and transmembrane domain proteins (MCTP) 3, 4, and 6 ER-PM tethers, and phosphatidylinositol-4-phosphate (PI4P) lipid. Graded PI4P amounts regulate MCTP docking to the PM, their plasmodesmata localization and cell-cell permeability. SAC7, an ER-localized PI4P-phosphatase, regulates MCTP4 accumulation at plasmodesmata and modulates cell-cell trafficking capacity in a cell-type specific manner. Our findings expand MCS's functions in information transmission, from intracellular to intercellular cellular activities. Overall design: mRNA profiles in the roots of 5-day old seedlings from wild-type (Col0), mctp4-1 single mutant (M6), mctp3-2 single mutant (M8) and mctp3-2/mctp4-1 double mutant (C2) Arabidopsis thaliana were generated by deep sequencing, in quadruplicates, on Illumina NovaSeq 6000 platform