PARENT SESSION
Posters P2D Marine photosynthesis and production. Abstracts (711-719)

Functional analysis of Prochlorocococcus pigment-binding proteins. Anne Rediger^*,1, Ilka Axmann¹, Wolfgang R. Hess^{1, 2}, ¹ Humboldt-University Berlin, Institute of Biology/Genetics, Berlin, Germany² University Freiburg, Experimental Bioinformatics, Freiburg, Germany

ABSTRACT- Prochlorococcus , the most abundant genus of photosynthetic organisms, owes its remarkably large depth distribution in the oceans to the occurrence of distinct ecotypes adapted to either low– or high-light niches. A significant fraction of the total chlorophyll in marine ecosystems belongs to the distinct light-harvesting antenna systems of this single genus. The Pcb proteins in these antenna systems form concentric rings around PSI in the high light adapted Prochlorococcus MED4 [1] and around PSI and II in the ultra-low light adapted Prochlorococcus SS120 [2]. In the moderately low-light adapted strain MIT 9313, only under iron stress an antenna system is formed for PSI whereas the PSII antenna is constitutive [2]. The pcb gene copy numbers are quite divers: 1 in MED4, 2 in MIT 9313 [3] and 8 in SS120 [4]. Thus, the synthesis and regulation of expression of these proteins might underlie sophisticated mechanisms. In the centre of our work is the development of tools to study the biosynthesis of these pigment-protein complexes. Transcription initiation sites of all pcb genes were mapped in the different strains to obtain insights into the regulation of transcription in Prochlorococcus. We have raised two different polyclonal peptide antisera against Prochlorococcus PcbA of MIT 9313 and PcbA of MED4 which monitor Pcb level with high specificity and sensititivity. To construct an experimental platform for functional analysis, the pcbA gene from Prochlorococcus MIT9313 under control of the Synechocystis psbA2 promotor was introduced within the open reading frame slr0168 in a glucose-tolerant strain of Synechocystis sp. PCC 6803. Northern blot analysis revealed a stable transcript accumulation of pcbA in Synechocystis. However, the co-expression of a candidate (DV) chlorophyll b biosynthesis enzyme has not resulted in the detection of Chl b bound to Pcbs in these strains yet. [1] Bibby TS, Nield J, Partensky F, Barber J. (2001) Nature. 413, 590. [2] Bibby TS, Mary I, Nield J, Partensky F, Barber J. (2003) Nature 424, 1051-4. [3] Rocap G, et al. (2003) Nature 424, 1042-7. [4] Dufresne et al. (2003) Proc Natl Acad Sci USA 100, 10020-5.

KEY WORDS: light-harvesting, cyanobacteria, chlorophyll