Łucja Kowalewska (Gyroid focus session)Gyroid- and Diamond-Type Membrane Configurations of Plants – Where Geometry Defines the Biological Function*

Cellular membranes have the ability to self-organize into several different morphologies, among which the most complex are periodic arrangements called cubic membranes, showcasing a remarkable blend of biological form and geometry. These cubic membranes resemble triply-periodic minimal surfaces (TPMS), well known in differential geometry. Although such complex membrane arrangements have been reported in different organisms from protozoa to mammals, the knowledge of the structural and molecular mechanisms leading to their formation and further transformation into other membrane morphologies is limited. Due to the lengthscale of cubic membranes (around 50–500 nm) and their fluid nature, 2D and 3D transmission electron microscopy (TEM) is the analysis method of choice to decipher their nanostructural features.

In our studies, we use the internal membranes of plant plastids as a model to investigate cubic morphologies. Plastids are a diverse group of organelles present in different plant organs. They fulfill various functions tightly connected to their inner membrane networks, photosynthesis being the most prominent one. We study the structure-composition interplay in cubic and lamellar arrangements self-organizing during plastid ontogenesis to understand how changes in the membrane composition influence formation and maintenance of such unique membrane assemblies.

In my talk, I will present how we recognize and annotate cubic assemblies using our SPIRE software tool, which enables the identification of bicontinuous membrane structures from TEM sections through interactive matching by comparison to mathematical “nodal surface” models. I will also discuss the specific features, assembly mechanisms, and biological function of two physiologically important examples of cubic membranes in plant plastids - the Diamond-shaped prolamellar body of the etioplast occurring naturally during plant development and Double-gyroid thylakoid assembly transiently present in fully developed and photosynthetically active chloroplast.