Intracellular morphogenesis of diatom silica is guided by local variations in membrane curvature

Silica cell wall formation in diatoms is a showcase for the ability of
organisms to control inorganic mineralization. The process of
silicification by these unicellular algae is tightly regulated within a
membrane-bound organelle, the silica deposition vesicle (SDV). Two
opposing scenarios were proposed to explain the tight regulation of this
intracellular process: a template-mediated process that relies on
preformed scaffolds or a template-independent self-assembly process. The
present work points to a third scenario, where the SDV membrane is a
dynamic mold that shapes the forming silica. We use in-cell cryo-electron
tomography to visualize the silicification process in situ, in its native
state, and with a nanometer-scale resolution. Significantly, this revealed
that the plasma membrane interacts with the SDV membrane via physical
tethering at membrane contact sites, where the curvature of the tethered
side of the SDV membrane mirrors the intricate silica topography. We
propose that silica growth and morphogenesis result from
crosstalk between membranes and their biophysical properties.