Data for: Exocytosis of the silicified cell wall of diatoms involves extensive membrane disintegration

Diatoms are unicellular algae, characterized by silica cell walls. The
silica elements are formed intracellularly in a membrane-bound silica
deposition vesicle (SDV), and are exocytosed after completion. How diatoms
maintain membrane homeostasis during the exocytosis of these large and
rigid silica elements is a long-standing enigma. We studied membrane
dynamics during cell wall formation and exocytosis in two model diatom
species, using live-cell confocal microscopy, transmission electron
microscopy and cryo-electron tomography. Our results show that during the
formation of the mineral phase it is in tight association with the SDV
membranes, which are forming a precise mold of the delicate geometrical
patterns. During exocytosis, the distal SDV membrane and the plasma
membrane gradually detach from the mineral and disintegrate in the
extracellular space, without any noticeable endocytic retrieval or
extracellular repurposing. Within the cell, there is no evidence for the
formation of a new plasma membrane, thus the proximal SDV membrane becomes
the new barrier between the cell and its environment, and assumes the role
of a new plasma membrane. These results provide direct structural
observations of diatom silica exocytosis, and point to an extraordinary
mechanism in which membrane homeostasis is maintained by discarding,
rather than recycling, significant membrane patches.