Poster: Organelle Biogenesis

Abs # 1163: Three-dimensional structure of the cyanobacterium Synechocystis sp. PCC 6803 using electron tomography

Presenter:	van de Meene, Allison ML, avandemeene@asu.edu
Authors	van de Meene, Allison ML (A)   Vermaas, Wim FJ (A)   Roberson, Robert W (A)
Affiliations:	(A): Arizona State University

Cyanobacteria are among the most ancient organisms on earth and are the probable progenitors to all plastids. Synechocystis sp. PCC 6803 is a model cyanobacterial system; the complete genome has been sequenced and many studies of cell processes such as photosynthesis have been undertaken. However, relatively little work has been done on the ultrastructure of this species. We have investigated the three-dimensional structure of the wild-type cell using cryofixation, transmission electron microscopy and electron tomography. The greater Z-axis resolution enabled by tomography provides fine detail of cell components including the elaborate three-dimensional array of thylakoid membranes that follow the periphery of the cell and converge at various sites adjacent to the cytoplasmic membrane. These sites vary in morphology and include cylindrical thylakoid centers and vesicles closely appressed to the cytoplasmic membrane; this close association suggests a role for these sites in thylakoid biogenesis. The thylakoid membranes are layered in expansive sheets that often appear to interconnect; these connections are most obvious around the regions of convergence and near the constriction site during cell division. The position and three-dimensional arrangement of the cytoplasmic inclusions is more obvious when the data is segmented with three-dimensional analysis software such as the IMOD software program. One example is the distribution of ribosomes within the cytoplasm, which has revealed an apparent ribosome exclusion zone around the thylakoid membranes. These results may offer insights into the biology of chloroplasts such as how thylakoid membranes form, how these membranes may be interconnected and how structures such as ribosomes are distributed within the organelle.