A talk by Tanai Cardona, Imperial College London.

Early evolution of photosynthetic water oxidation

When and how photosynthesis originated are questions that still remain unanswered. It is generally accepted that anoxygenic photosynthesis predates oxygenic photosynthesis by a long time, with various estimates ranging from several hundred million years to more than a billion years. I will show how the evolution of the photosynthetic machinery is in contradiction with such a scenario. I will also show how the origin of photosynthetic water oxidation to oxygen, the hallmark of oxygenic photosynthesis, can be traced back to some of the earliest events in the evolutionary history of life. My arguments are based on straightforward sequence and structural comparisons of the core proteins of the photosystems, in combination with molecular phylogenies and Bayesian molecular clocks. I will present my attempts to understand the evolution of oxygenic photosynthesis as a function of time and to build a relative timeline of key events in the evolution of the photosynthetic machinery, such as the origin of the Mn₄CaO₅ water-oxidising/oxygen-evolving cluster of Photosystem II. I will argue that the earliest forms of oxygenic photosynthesis are likely to be as old as the earliest forms of anoxygenic photosynthesis and therefore emerging in the early Archean long before the Great Oxidation Event.

NB This event is only open to University of Bristol staff and students.