Cell division is a fundamental process for living organisms to sustain growth and development.

In plants, cells divide following incomplete cytokinesis (physical separation of daughter cells), leading to the creation of hundreds of pores called plasmodesmata (PD). PD operate as a route for cell-to-cell communication and molecular exchange between neighbouring cells. PD bridges allow cytosolic, plasma membrane (PM), and endoplasmic reticulum (ER) continuities to be maintained across daughter cells. However, the molecular mechanisms underlying PD assembly remain unclear. Recently, our team identified MULTIPLE C2 DOMAIN AND TRANSMEMBRANE REGION PROTEINS (MCTP) that could act as PM-ER tethers within PD bridges. In this study, we addressed the question of how plant cells establish endomembrane and cytosolic cell-to-cell continuity while dividing. Using advanced microscopy, we found that PD bridge formation requires integration of the endoplasmic reticulum (ER) across cell plate fenestrae. Indeed, ER marks the position of the nascent PD and stabilizes it. In addition, we observed that MCTP3, 4 and 6 are necessary for PD formation and are involved in the shaping and anchoring of ER within the nascent membrane bridges. Our work sheds light on the molecular mechanisms by which plant cells go through incomplete division to allow intercellular communication.