PARENT SESSION

Symposium S7B Evolution of photosynthesis
Thursday September 2nd, 2004 2:40 PM-4:40 PM Room 511D
Chair: Beverley Green
Co-Chair: Bob Blankenship

Evolution of Oxygenic Photosystems. Jason Raymond^*,1, Robert Blankenship¹, ¹ Department of Chemistry and Biochemistry, Tempe, AZ, USA

ABSTRACT- The cyanobacterial photosynthetic apparatus represents a pinnacle of biological innovation, having evolved the unique ability to couple photon absorption to the processes of water oxidation, proton motive force generation, and the transfer of reducing equivalents for carbon fixation. At the core of the photosynthetic apparatus are photosystems I and II, two intricate protein complexes comprised of several dozen subunits, most of which have no homologous counterparts in any other system. The history of cyanobacterial photosystems may extend more than 2.7 billion years into the past, and recent structural data have provided unequivocal evidence that the core reaction center proteins of both photosystems arose from a single ancestral complex via gene duplication. Using comparative genomics and molecular evolutionary analyses, we are investigating how the two modern cyanobacterial photosystems plausibly arose from a much simpler reaction center/antenna complex perhaps not unlike that found in extant anoxygenic phototrophs. Our analysis provides insight into several important questions in the evolution of cyanobacterial photosystems, including how and when the expansion of peripheral protein subunits occurred, why some elements of these complexes have been so recalcitrant to change, and how sequence/structure divergence has been important in the establishment of heterodimeric reaction centers. Furthermore, we address the inherent limitations of sequence analysis in addressing questions such as the fission versus fusion hypothesis on the evolution of photosystems I and II.

KEY WORDS: Photosystem I, Evolution, Photosystem II