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SUMMARY:The first cyanobacterium. A redox switch hypothesis for the origin
  of oxygenic photosynthesis. - Professor John Allen\, Queen Mary\, Univers
 ity of   London
DTSTART:20070201T160000Z
DTEND:20070201T170000Z
UID:TALK6017@talks.cam.ac.uk
CONTACT:3901
DESCRIPTION:Photosynthesis provides energy in the Earth's biosphere and ox
 ygen in its atmosphere. For oxygen to be produced\, two different light re
 actions must operate simultaneously\, and in series. Known anaerobic\, pho
 tosynthetic bacteria contain one or other of these photosystems\, but neve
 r both. I propose that the two photosystems diverged\, in structure and fu
 nction\, from a common ancestor\, within a single\, continuous\, anaerobic
  lineage. In such cells\, the two photosystems are isoenzymes encoded by o
 rthologous genes under co-ordinated\, redox regulatory control. A redox sw
 itch responds to defined environmental conditions and selects which set of
  genes is expressed. In these cells\, the two photosystems are thus synthe
 sised at different times. It is further proposed that the origin of oxygen
 -evolving photosynthesis was a simple mutation that disabled the redox swi
 tch\, permitting simultaneous expression of the two sets of genes. The two
 \, newly co-existing photosystems became connected by shared electron carr
 iers\, allowing generation of electrochemical potential high enough to oxi
 dise water\; an inexhaustible supply of reductant\; and the selective adva
 ntages\, and pressures\, of an aerobic world.\n\nThe redox switch hypothes
 is predicts a specific redox regulatory control pathway in a Heteronuclear
 \, Anoxygenic Phototroph - "HAP". "Heteronuclear" denotes the possession o
 f genes for both type I and type II reaction centres\, a property previous
 ly thought to be restricted to oxygenic phototrophs. The predicted organis
 m will share some of the characteristics of Chloroflexus and Oscillatoria 
 spp. It is possible that all such lineages have died out\, but this seems 
 unlikely\, since suitable habitats still exist. It is therefore to be expe
 cted that this bacterium is either undiscovered\, or a known species\, as 
 yet incompletely described. "HAP" is also a good candidate for the organis
 m that built ancient stromatolites and other microbialites in the early Ar
 chaean\, up to 1 Gyr before the rise in atmospheric oxygen concentration a
 t 2.5 to 2.6 Gyr before the present day. Elements of the redox regulatory 
 control pathway are likely to have been conserved\, and may govern the rel
 ative activities of the two light reactions in cyanobacteria and chloropla
 sts.\n\nAllen JF: A redox switch hypothesis for the origin of two light re
 actions in photosynthesis. FEBS Letters 2005\, 579: 963- 968. \n\nhttp://j
 fa.bio.qmul.ac.uk/
LOCATION:Department of Plant Sciences\, Large Lecture Theatre
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