Assembly and Dynamics of Photosynthetic Membranes

The light-dependent reactions of oxygenic photosynthesis in algae and plants are catalyzed by a series of thylakoid membrane protein complexes in chloroplasts. Although high-resolution structures are now available for the major complexes, a thorough understanding of photosynthetic membrane biogenesis, regulation, and repair is lacking. We are using genetics, advanced imaging, and modeling to investigate these dynamic processes.

To gain insight into how specific pigments, proteins, lipids, and cofactors are assembled into a functional photosynthetic membrane, we have isolated hundreds of new Chlamydomonas mutants that affect photosynthesis, many of which are defective in conserved genes of previously unknown function. We have found mutants affecting key reactions in chlorophyll biosynthesis and nearly every step of carotenoid biosynthesis, in addition to mutants that affect specific photosynthetic complexes. With support from the Community Science Program at JGI (http://jgi.doe.gov/photosynthesis-in-chlamydomonas/), we have re-sequenced this collection of mutants to identify all the genes that are affected in each mutant, and we have embarked on the detailed characterization of individual mutants, often in collaboration with labs that have a particular interest in specific genes.

Biogenesis, regulation, and repair of the photosynthetic apparatus in chloroplasts involves nano- to micro-scale reorganization of the photosynthetic membrane and its protein complexes. To obtain a detailed molecular description of the organization and dynamics of the photosynthetic membrane, we are using advanced imaging approaches such as live-cell super-resolution microscopy, electron microscopy and tomography, atomic force microscopy. For example, with the labs of Eva Nogales (HHMI, UC-Berkeley, and LBNL) and Harald Hess (HHMI Janelia Research Campus), we have employed focused ion beam scanning electron microscopy (FIB/SEM) to study the three-dimensional ultrastructure of Chlamydomonas cells.