PhD ceremony Mr. B. Drop: From photosystem I to photosystem II. Travelling across the thylakoid membrane of Chlamydomonas reinhardtii with LHCII

PhD ceremony: Mr. B. Drop

Dissertation: From photosystem I to photosystem II. Travelling across the thylakoid membrane of Chlamydomonas reinhardtii with LHCII

Promotor(s): prof. R. Croce

Faculty: Mathematics and Natural Sciences

The purpose of this thesis is to provide a comprehensive picture of the structural and functional properties of Photosystem I (PSI) and Photosystem II (PSII) supercomplexes of the green alga Chlamydomonas reinhardtii and to test their flexibility in different environmental conditions.

Novel PSI and PSII complexes have been purified and characterized, allowing relating the protein composition and organization to the functional behavior of the supercomplexes. PSI complex contains a core complex and a light harvesting antenna system composed of nine Lhcas organized on one side of the core in a double half-ring arrangement. The novel PSII-LHCII supercomplex contains six LHCII trimers per dimeric core. The results show that capacity of both Photosystem I and Photosystem II in C. reinhardtii is larger than that of the photosystems of plants. To adapt to changing light conditions, the light harvesting capacity of PSI and PSII is modulated, to maximize photosynthesis and minimize photodamage. PSI in state 2, is able to bind two LHCII trimers and one monomer, in addition to its nine Lhcas. This is the largest PSI complex ever observed, far larger than that of higher plants where only one LHCII trimer was found to be associated with PSI in state 2. The information obtained represents the basis for a full understanding of light-harvesting and its regulation in this alga.