Three-Dimensional Visualization of the Tubular-Lamellar Transformation of the Internal Plastid Membrane Network during Runner Bean Chloroplast Biogenesis

Abstract

Chloroplast biogenesis is a complex process that is integrated with plant development, leading to fully differentiated and functionally mature plastids. In this work, we used electron tomography and confocal microscopy to reconstruct the process of structural membrane transformation during the etioplast-to-chloroplast transition in runner bean (Phaseolus coccineus). During chloroplast development, the regular tubular network of paracrystalline prolamellar bodies (PLBs) and the flattened porous membranes of prothylakoids develop into the chloroplast thylakoids. Three-dimensional reconstruction is required to provide us with a more complete understanding of this transformation. We provide spatial models of the bean chloroplast biogenesis that allow such reconstruction of the internal membranes of the developing chloroplast and visualize the transformation from the tubular arrangement to the linear system of parallel lamellae. We prove that the tubular structure of the PLB transforms directly to flat slats, without dispersion to vesicles. We demonstrate that the grana/stroma thylakoid connections have a helical character starting from the early stages of appressed membrane formation. Moreover, we point out the importance of particular chlorophyll-protein complex components in the membrane stacking during the biogenesis. The main stages of chloroplast internal membrane biogenesis are presented in a movie that shows the time development of the chloroplast biogenesis as a dynamic model of this process.

Nature‐Inspired Design and Application of Lipidic Lyotropic Liquid Crystals

“…From a functional viewpoint, the transition from the bicontinuous prolamellar body to the lamellar stacking is interesting, as it is triggered by light and is accompanied by the emergence and incorporation of the multisubunit, rigid membrane protein complexes responsible for photosynthesis. However, this light–matter interaction is not a photonic crystal effect due to the geometric structure of the prolamellar body; the length scale of the structure is substantially too small (e.g., 78 nm for the maize PLB) to create a photonic effect in the biologically relevant spectrum of light; similarly, the spacing of the grana lamellar stacking is of the order of a typical bilayer width and hence also much too small to cause photonic crystal effects; note that in some related iridoplast systems a spacing compatible with optical effects is generated through multilayer stacks . The purpose of the complex structural shape remains unknown, however it has been observed that stacked thylakoid membranes increase photosynthetic efficiency .…”

“…All data to date stem from post vivo imaging, in stained and fixed tissue, or freeze‐fracture microscopy. With ever improving microscopy methods for living tissue and intracellular membrane organelle organization, both in vivo and post vivo (e.g., for the endoplasmic reticulum and for the prolamellar body in plants), we are likely to soon see a surge in structural data for biological nanostructured phases that will allow us to fully realize just how important they are in nature's building blocks of the nanoorganization of living materials. Since Dubochet et al invented the cryo‐TEM technique about 35 years ago, it has evolved substantially and recently enabled greater insight into artificially made lyotropic liquid crystalline phases using also tomography, averaging techniques to obtain 3D reconstruction and increase resolution .…”

Three-Dimensional Analysis of Chloroplast Structures Associated with Virus Infection

“…Chloroplast biogenesis is a complex process and is highly integrated with cellular and plant development (Yang et al, 2010;Pogson et al, 2015). Although three-dimensional (3D) models of the thylakoid membrane architecture have been created using electron tomography of higher plant chloroplasts (Shimoni et al, 2005;Daum et al, 2010;Austin and Staehelin, 2011;Kowalewska et al, 2016) and Chlamydomonas reinhardtii chloroplasts (Engel et al, 2015), a 3D visualization of chloroplast changes in response to external stresses (e.g. viral attack) has not been investigated.…”

TSC1 enables plastid development under dark conditions, contributing to rice adaptation to transplantation shock

“…Conditions that limit light, such as being covered by soil or litter (Solymosi and Aronsson 2013), also result in the formation of etioplasts. However, etioplasts transform into chloroplasts after short-term exposure to light (Kowalewska et al 2016).…”