PARENT SESSION

Symposium S4C Controlling CO₂: Stomates and carbon concentrating mechanisms
Tuesday August 31st, 2004 2:40 PM-4:40 PM Room 510A
Chair: George Espie
Co-Chair: Murray Badger

Response to low carbon dioxide in the glaucocystophyte alga, Cyanophora paradoxa. Suzanne Burey^*,1, Valeriy Poroyko², Neslihan Ozturk², Sara Fathi-Nejad¹, Gisela Hammerschmied¹, Christoph Schueller¹, Hans Bohnert², Wolfgang Loeffelhardt¹, ¹ Max F. Perutz Laboratories, Vienna, Austria² Departments of Plant Biology and Crop Sciences, Urbana, IL, USA

ABSTRACT- Cyanophora paradoxa is the best investigated member of the glaucocystophyte algae, the most primitive phototrophic eukaryotes whose plastids (cyanelles) are surrounded by a peptidoglycan layer, a clear indication of their descent from endosymbiotic cyanobacteria. As many aquatic microorganisms which as a group contribute about 50% to global CO₂ fixation, C. paradoxa possesses an inorganic carbon concentration mechanism (CCM). Increase of the CO₂ level in CCM microcompartments harboring Rubisco increases the efficiency of photosynthetic carbon fixation. Operation of the CCM is triggered by growth at ambient (0.04%) CO₂ concentrations with concomitant induction of CO₂ and bicarbonate transporters and components of these microcompartments. These electron-dense structures are carboxysomes in prokaryotes and pyrenoids in eukaryotic algae. We postulate that the cyanelles of C. paradoxa did retain another prokaryotic feature in addition to the peptidoglycan wall: the unique case of an eukaryotic carboxysome. An isolation procedure for carboxysomes was developed enabling a proteomics approach and the identification of carboxysome proteins other than Rubisco. Rubisco activase was imported into isolated cyanelles and was shown to integrate into carboxysomes. Two cDNA libraries of cells grown under ambient and high CO₂ were established for sequencing and annotation of more than 5000 ESTs. Of these, 2300 unique ESTs were chosen for microarray printing. Hybridizations with RNA from high and low (various timepoints after downward shift) CO₂ grown cells were performed. Around 450 genes were differentially expressed under high and ambient CO₂. The potential involvement of the corresponding gene products in the CCM of C. paradoxa will be discussed.

KEY WORDS: microarrays, ccm, cyanophora paradoxa, carboxysome